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Abstract

Many studies have analyzed muscle activity during different strength exercises. Although the leg press (LP) is one of the most common exercises performed, there is little evidence of lower limb muscle activity patterns during this exercise and its variations. Thus, this study aimed to verify how mechanical changes and loads affect lower limb muscle activity during the performance of different LP exercises. Fourteen women performed 3 LP exercises: 45 degrees LP (LP45), LP high (LPH), and LP low (LPL) at 40% and 80% of the 1 repetition maximum. The electromyographic activity of the rectus femoris, vastus lateralis, biceps femoris, gastrocnemius, and gluteus maximus was recorded. Results suggested that mechanical changes affect lower limb muscle activity and that it is related to the load used. At moderate effort levels, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than during the LPH. At a high effort level, the rectus femoris and vastus lateralis (quadriceps) were more active during the LPL than the LPH. Again, the rectus femoris and gastrocnemius were more active during the LP45 and LPL than the LPH. On the other hand, gluteus maximus activity was greater during the LPH than the LPL. This study found that coordination patterns of muscle activity are different when performing LP variations at high or moderate effort levels because of mechanical changes and different loads lifted during the different LP exercises. These results suggest that if the goal is to induce greater rectus femoris and vastus lateralis (quadriceps) activation, the LPL should be performed. On the other hand, if the goal is to induce gluteus maximus activity, the LPH should be performed.

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... Different studies have shown that muscle activation varies during multi-joint, lower-body strength training exercises depending on the intensity [6,12] and the variants of the exercise itself [12]. The leg press is performed using closed-chain kinetic effort [13] and the hip and knee extension involves large lower-body muscle groups (the quadriceps, hamstring, gluteus, and gastrocnemius) [14]. The specific training of these muscle groups is closely related to jumping, running, and athletic performance in general [15]. ...
... Specifically, the leg press and its variants are some of the exercises studied in the scientific literature [14,15,[20][21][22]. Previous studies have found that the knee flexion angle had a significant effect on muscle activation in the bilateral leg press [21,22]. ...
... Additionally, certain variations in technique need to be considered when training using the leg press and its variants. For instance, feet position on the footplate, regarding lower and higher feet placement [14,15] or width stance [15] have been some studied variants of leg press. For example, leg press with high feet placement on the footplate showed higher gluteus maximus activity compared to low feet placement [14]. ...
Article
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The aim of this study was to analyze the literature on muscle activation measured by surface electromyography (sEMG) of the muscles recruited when performing the leg press exercise and its variants. The Preferred Reporting Items of Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed to report this review. The search was carried out using the PubMed, Scopus, and Web of Science electronic databases. The articles selected met the following inclusion criteria: (a) a cross-sectional or longitudinal study design; (b) neuromuscular activation assessed during the leg press exercise, or its variants; (c) muscle activation data collected using sEMG; and (d) study samples comprising healthy and trained participants. The main findings indicate that the leg press exercise elicited the greatest sEMG activity from the quadriceps muscle complex, which was shown to be greater as the knee flexion angle increased. In conclusion, (1) the vastus lateralis and vastus medialis elicited the greatest muscle activation during the leg press exercise, followed closely by the rectus femoris; (2) the biceps femoris and the gastrocnemius medialis showed greater muscular activity as the knee reached full extension, whereas the vastus lateralis and medialis, the rectus femoris, and the tibialis anterior showed a decreasing muscular activity pattern as the knee reached full extension; (3) evidence on the influence of kinematics modifications over sEMG during leg press variants is still not compelling as very few studies match their findings.
... 31,38,45 Surface electromyography (sEMG) has been widely used in research 5 as a noninvasive method for assessing muscle activation and neuromuscular function. 6,11,17 This has resulted in studies assessing the muscle activation during the horizontal leg press, [16][17][18]46,50,52 unilateral leg press, 6 and inclined leg press. 11,26 The muscles most frequently assessed using sEMG during the leg press exercise are the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), and biceps femoris. ...
... 6,11,17 This has resulted in studies assessing the muscle activation during the horizontal leg press, [16][17][18]46,50,52 unilateral leg press, 6 and inclined leg press. 11,26 The muscles most frequently assessed using sEMG during the leg press exercise are the vastus medialis oblique (VMO), vastus lateralis (VL), rectus femoris (RF), and biceps femoris. 13,26,28,50,52 In addition, some other studies have evaluated the leg press exercise using different feet stances (conditions) over the footplate. ...
... 13,26,28,50,52 In addition, some other studies have evaluated the leg press exercise using different feet stances (conditions) over the footplate. For instance, a low feet position over the footplate resulted in greater quadriceps muscle activation, 11 whereas there were no differences in overall muscle activation between the 30° forefoot external rotation condition and wide and narrow feet stances. 13 Nonetheless, the effect that these conditions may trigger on muscle activation at different movement velocities (MVs) has not yet been clearly identified. ...
Article
Background: The leg press is one of the most typical exercises for strengthening the lower limbs. The objectives of this study were to compare 5 inclined leg press exercise conditions, varying the feet width stance (100% or 150% hip width), the feet rotation (0° or 45° external rotation) on the footplate and using 2 different movement velocities (MVs; maximum intended, and 2:2 seconds steady-paced velocities) to determine their effect on muscle activation as well as on the kinematic parameters between trained men and trained women. Hypotheses: There will be no significant differences in muscle activation with regard to the feet position. The higher the MV, the greater the muscle activation. Study design: A cross-sectional cohort study. Level of evidence: Level 3. Methods: A repeated-measures between-group design was performed to examine muscle activation and kinematic parameters for the different conditions between gender groups. The level of significance was set at alpha = 0.05 for all statistical analyses. Results: Muscle activation presented no differences between conditions regarding feet width stance or feet rotation. Furthermore, muscle activation was greater during positive phases than negative phases of the exercise for all conditions and was also greater under maximum intended velocity conditions compared with steady-paced conditions. Otherwise, the muscle activation pattern presented slight differences by gender. In men, the greatest muscle activation was for the vastus medialis, followed by the vastus lateralis (VL), rectus femoris (RF), and gluteus medialis (GMED), while in women, the greatest muscle activation was for the vastus medialis, followed by the RF, VL, and GMED. Finally, greater mean propulsive velocity, maximum velocity, maximum power, and footplate displacement values were reported for men than for women under all the conditions. Conclusion: The inclined leg press exercise produces the highest muscle activation in the vastus medialis, regardless of the velocity, feet stance, or gender. Clinical relevance: Given that there are no differences in muscle activation regarding the feet stance, a participant's preferred feet stance should be encouraged during the inclined leg press exercise. Furthermore, the MV would preferably depend on the session objective (a training or a rehabilitation program), being aware that there is greater muscle activation at higher speeds. The inclined leg press exercise could be performed as a closed kinetic chain exercise when the main objective is to activate the vastus medialis.
... Therefore, the detection and quantification of this activation pattern and consequent strength deficits are essential for the evaluation of subsequent therapies or the efficiency of physical training on daily living activities or athletic performance 9 . However, previous studies have only investigated the muscle activity or strength parameters of LP exercise adopting one set, using maximal loads or performing isometric dynamic tasks 2,4,6,7,10 . On the other hand, traditional rehabilitation programs are often composed by multiple sets using submaximal loads 3,[11][12][13] . ...
... Root mean square (RMS) together with the mean and/or median frequency of the SEMG power spectrum has been often adopted in previous studies to evaluate muscle fatigue 2,4,6,20 . However, to overcome the limitation of low sensitivity in these spectral parameters, a spectral index with greater sensitivity, called the FInsm5, was adopted to assess changes in muscle EMG during fatigue 21 . ...
... However, the BF muscle showed lower levels surface EMG amplitude and fatigue indices among sets and protocols. These data are in agreement with previous evidence which indicated lower activation levels of BF muscle during LP and squat exercises, when compared to quadriceps muscles 2,9,28,29 . ...
Article
Full-text available
Study design: Crossover design. Context: Excessive valgus and varus force which affected the knee joint during dynamic tasks has been often associated to lower extremity injuries. Strategies to increase the resistance against these asymmetries (eg, the use of a physioball between the knees or elastic bands around the knees) are often applied in rehabilitation and conditioning programs. Objective: The purpose of this study was to investigate the effect of performing leg press (LP) 45° using a physioball and elastic band over multiple sets with submaximal loads on electromyographic (EMG) amplitude and fatigue indices. Methods: 18 trained females volunteered (age: 24.4 ± 2.1 y; height: 168.1 ± 4 cm; body mass: 65.1 ± 4.4 kg) participated in this study. The 10 repetition maximum (RM) loads were determined for the LP. Then, 3 experimental protocols were followed in a randomized crossover design over 3 nonconsecutive days: control protocol-the participants performed 4 LP sets; physioball between knees-4 LP sets were performed with the physioball between the knees; elastic band-4 LP sets were performed with the elastic band involving the knees. Ten repetitions were performed during each set with 70% of 10-RM loads; EMG spectral indices (CRMS and Cf5) was collected from the biceps femoris (BF), vastus lateralis (VL), vastus medialis obliquus (VMO), and rectus femoris (RF) muscles. Results: Higher levels of CRMS and Cf5 were noted for RF, VL, and VM muscles using the physioball and elastic band when compared with control protocol, respectively. CRMS index of BF muscle was significantly higher using physioball and elastic band protocol versus control condition, respectively. Conclusion: Therefore, both physioball and elastic band can be adopted during LP with the goal to reduce excessive varus and valgus forces, respectively, even performing consecutive sets with submaximal loads. Furthermore, this may be an interesting alternative to increasing quadriceps activation and improving the knee joint stabilization.
... Therefore, the detection and quantification of this activation pattern and consequent strength deficits are essential for the evaluation of subsequent therapies or the efficiency of physical training on daily living activities or athletic performance 9 . However, previous studies have only investigated the muscle activity or strength parameters of LP exercise adopting one set, using maximal loads or performing isometric dynamic tasks 2,4,6,7,10 . On the other hand, traditional rehabilitation programs are often composed by multiple sets using submaximal loads 3,[11][12][13] . ...
... Root mean square (RMS) together with the mean and/or median frequency of the SEMG power spectrum has been often adopted in previous studies to evaluate muscle fatigue 2,4,6,20 . However, to overcome the limitation of low sensitivity in these spectral parameters, a spectral index with greater sensitivity, called the FInsm5, was adopted to assess changes in muscle EMG during fatigue 21 . ...
... However, the BF muscle showed lower levels surface EMG amplitude and fatigue indices among sets and protocols. These data are in agreement with previous evidence which indicated lower activation levels of BF muscle during LP and squat exercises, when compared to quadriceps muscles 2,9,28,29 . ...
... Peng et al. [12], on the other hand, reported higher medial thigh muscle activation in a male population during the leg press with hip adduction resistance, compared to the conventional leg press. Despite the above, the literature on sEMG assessment of leg press exercise conditions remains scarce, especially in the female population [4,[13][14][15]. Muscle activation has only been assessed in the this population while implementing extra hip adduction/abduction resistance conditions during the leg press [4], and different feet height positions on the footplate [14]. ...
... Despite the above, the literature on sEMG assessment of leg press exercise conditions remains scarce, especially in the female population [4,[13][14][15]. Muscle activation has only been assessed in the this population while implementing extra hip adduction/abduction resistance conditions during the leg press [4], and different feet height positions on the footplate [14]. However, no study to date has evaluated whether stance width (100-150% hip-width distance) and feet rotation (0-45 • external feet rotation) would elicit any changes in muscle activation in the female population when performing the inclined leg press at different movement velocities (controlled velocity and maximal intended velocity). ...
... A previous study conducted on a female population agreed with our results regarding muscle activation-Da Silva et al. [14] reported similar muscle activation for the RF and VL during the flat leg press and the inclined leg press performed at an 80% 1RM intensity in a young female population. They also encouraged the most comfortable feet stance on the footplate, but they did not analyze VMO muscle activation, thus providing an incomplete picture of overall quadriceps muscle activation during those exercises. ...
Article
Full-text available
Knee joint muscle activation imbalances, especially weakness in the vastus medialis oblique, are related to patellofemoral pain within the female population. The available literature presents the leg press as an exercise which potentially targets vastus medialis oblique activation, thus reducing imbalances in the quadriceps muscles. The main aim of the present study was to compare thigh muscle activation and kinematic parameters under different conditions during the inclined leg press exercise in a young female population. A cross-sectional study was conducted on 10 young, trained females. Muscle activation of the vastus medialis oblique, vastus lateralis, rectus femoris and gluteus medialis was analyzed under five different inclined leg press conditions, modifying the feet rotation (0-45 • external rotation) and the stance width (100-150% hip width) on the footplate. All the conditions were performed at two different movement velocities: controlled velocity (2" eccentric-2" concentric) and maximal intended velocity. Mean propulsive velocity, maximum velocity and maximum power were also assessed. The results show that both controlled velocity conditions and maximal intended velocity conditions elicited a similar muscle activation pattern with greater activation during the concentric phase (p < 0.001, ηp 2 = 0.96). The maximal intended velocity conditions showed greater overall muscle activation (p < 0.001, ηp 2 = 0.91). The vastus medialis oblique presented the greatest muscle activation, followed by the rectus femoris, vastus lateralis and, the gluteus medialis. Furthermore, the inclined leg press condition with 0º feet rotation, 100% hip width distance and the maximal intended velocity generated the greatest kinematic parameter outputs. In conclusion, the inclined leg press exercise might be an optimal exercise to target vastus medialis activation regardless of the feet rotation and stance width conditions.
... Kinematic analysis has also been used to compare DL technique of skilled and unskilled lifters (4). Although several studies have examined the DL, only a few researchers have investigated muscle activation during this exercise (5)(6)(7)(8). The DL and Sumo technique have been compared using electromyography (EMG) analysis. ...
... The increased MG activity during the ascent phase could be explained by an increased plantar flexion moment during this phase as shown by Escamilla et al. (2000) for the conventional style DL. Da Silva et al. (5) found that the gastrocnemius muscle is more activated during leg press exercise with low foot placement and 45° (near 80% of MVIC). This may have happened due to the increased plantar flexion movement in the two exercises. ...
Data
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The purpose of this study was to analyze eletromyographic (EMG) signal of biceps femoris (BF), vastus lateralis (VL), lumbar multifidus (LM), anterior tibialis (AT), and medial gastrocnemius (MG) during the deadlift (DL) and stiff-legged deadlift (SLDL). Fourteen men (26.71 ± 4.99 yrs; body mass 88.42 ± 12.39 kg; 177.71 ± 8.86 cm) voluntarily participated in this study. The data were obtained on three non-consecutive days separated by 48 hrs. In the first day, anthropometric measures and the repetition maximum testing (1 RM) for both exercises were applied in a counter-balanced cross-over design. On the second day, the 1 RM was re-tested. On the third day, both exercises were performed at 70% of 1 RM and the EMG data were collected. Parameters related to the RMS during the movement, temporal activation patterns, and relative times of activation were analyzed for each muscle. The maximum activation level for VL during the DL (128.3 ± 33.9% of the EMG peak average) was significantly different (P = 0.027) from the SLDL (101.1 ± 14% of the EMG peak average). These findings should be useful when emphasizing different muscle groups in a resistance training program.
... Kinematic analysis has also been used to compare DL technique of skilled and unskilled lifters (4). Although several studies have examined the DL, only a few researchers have investigated muscle activation during this exercise (5)(6)(7)(8). The DL and Sumo technique have been compared using electromyography (EMG) analysis. ...
... The increased MG activity during the ascent phase could be explained by an increased plantar flexion moment during this phase as shown by Escamilla et al. (2000) for the conventional style DL. Da Silva et al. (5) found that the gastrocnemius muscle is more activated during leg press exercise with low foot placement and 45° (near 80% of MVIC). This may have happened due to the increased plantar flexion movement in the two exercises. ...
Article
Full-text available
The purpose of this study was to analyze eletromyographic (EMG) signal of biceps femoris (BF), vastus lateralis (VL), lumbar multifidus (LM), anterior tibialis (AT), and medial gastrocnemius (MG) during the deadlift (DL) and stiff-legged deadlift (SLDL). Fourteen men (26.71 ± 4.99 yrs; body mass 88.42 ± 12.39 kg; 177.71 ± 8.86 cm) voluntarily participated in this study. The data were obtained on three non-consecutive days separated by 48 hrs. In the first day, anthropometric measures and the repetition maximum testing (1 RM) for both exercises were applied in a counter-balanced cross-over design. On the second day, the 1 RM was re-tested. On the third day, both exercises were performed at 70% of 1 RM and the EMG data were collected. Parameters related to the RMS during the movement, temporal activation patterns, and relative times of activation were analyzed for each muscle. The maximum activation level for VL during the DL (128.3 ± 33.9% of the EMG peak average) was significantly different (P = 0.027) from the SLDL (101.1 ± 14% of the EMG peak average). These findings should be useful when emphasizing different muscle groups in a resistance training program.
... Some characteristics of the leg press exercise can be highlighted to explain its strong correlation with both dependent variables. The leg press movement involves extensor muscles of the knee and hip and flexors of the knee (Silva et al., 2008). This movement is a closed kinetic chain, characterized by high resistance in the distal Table 1 Mean ± SD and coefficient of variation for bone mineral content (BMC) and strength parameters between men and women. ...
Article
The aims of this pilot study were to verify which tests of muscle strength better explains the bone mineral content (BMC) of the femoral neck and lumbar spine and to develop predictive equations to estimate femoral neck and lumbar spine BMC. Twenty nine subjects aged 56 to 76 years (12 women and 17 men) participated in the study. The femoral neck and lumbar spine BMC was evaluated by Dual X-ray absorptiometry (DXA). Muscle strength measurements included maximal isometric voluntary contraction of knee extensors and flexors, vertical jump, and 5-repetition maximum in the leg press (5-RMLP), seated leg curl (5-RMLC), and handgrip strength. Women presented a moderate to strong correlation between femoral neck BMC with 5-RMLP (r=0.819), 5-RMLC (r=0.879), knee extensors peak torque (r=0.699), and handgrip strength (r=0.663), as well as between lumbar spine BMC and the 5-RMLP test (r=0.845) and manual grip strength (r=0.699). The 5-RMLP and 5-RMLC tests better explained femoral neck BMC (R2=0.859) and the 5-RMLP test and body mass, lumbar spine density (R2=0.757) for females. Men did not present correlations between BMC and strength variables. The 5-RMLP and 5-RMLC variables explained better the variations of the femoral neck BMC, while 5-RMLP with the body mass better explained lumbar spine BMC for females. Future studies should evaluate a larger sample size and prioritize the strength tests with higher prediction capacity.
... However, the disadvantage is that these resistance machines do not require activation or engagement of any of the major stabilizer muscles and is a widely used exercise to strengthen the lower limbs. This test is performed using closed-chain kinetic effort [15], whereas knee extension involves large muscle groups of the lower body (i.e., quadriceps and hamstrings) [47]. This study has several limitations. ...
Article
Full-text available
Strength is essential for carrying out the usual activities of daily life. As there is a loss of strength in elderly, many treatments are based on delaying the loss of strength or maintaining it. Isokinetic dynamometry is the gold standard for assessing strength. It is essential that studies are conducted to allow us to identify the reliability of isokinetic strength assessments in older people. This study aimed to test the absolute and relative intra-session reliability of peak torque and work of a concentric knee extension-flexion performed at 60°/s in elderly. Fifty-two elderly subjects performed three repetitions of bilateral concentric knee extension-flexion at 60°/s using an isokinetic dynamometer. The relative and absolute reliability were calculated between the second and third repetition. The intra-class correlation coefficient values were between 0.94 and 0.98 for peak torque and work in all measures, which is considered “excellent”, except for left leg flexors in women, with values between 0.85 and 0.88, which is considered “good”. The standard error of measurement (SEM) percentage oscillated from 3.9% to 10.5%, with a smallest real difference (SRD) percentage of 10.9% to 29.2% for peak torque. The relative reliability of peak torque and work were excellent for all measures except flexors in women, evidencing the utility of isokinetic dynamometry for monitoring lower limb maximal muscle strength and work of concentric knee extension-flexion at 60°/s/s in the elderly. In addition, an SRD > 19.9% in peak torque and an SRD > 23.1% in work is considered a true change.
... It is important to note that in the knee extension, VM acts as a synergist with the VL. In this regard, recent study suggests that quadriceps muscle activity during leg press exercise depend upon and strongly vary with the knee angle, foot placement and effort level [209]. VM has been also shown to display nonlinear EMG/force relationship during isometric leg press exercise [210]. ...
Thesis
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Vibration stimulation has been used as a tool to relieve muscle pain and spasm in physical therapy for many years. However recently, vibration, mainly Whole Body Vibration (WBV), has been increasingly studied and used as an exercise intervention in sports and rehabilitation. Although the physiological mechanisms which guide the body’s response to this exercise modality are relatively poorly understood, evidence indicates that vibration can enhance muscle strength, power, and flexibility as well as increase bone mineral density in the general population. Evidence also suggests that the neuromuscular response to vibration stimulation depends on muscle length, stretch level (contraction) along with the vibration characteristics. One way to alter muscle length and contraction levels while receiving vibration is to superimpose the stimulation on graded isometric contraction. However, current WBV device designs cannot facilitate the delivery of vibration stimulation superimposed on graded isometric voluntary contraction. The aim of this PhD project was twofold, firstly to develop and evaluate a prototype WBV device which enables the delivery of vibration stimulation that can be superimposed on graded isometric contraction and secondly, to assess the neuromuscular responses to vibration superimposed on graded isometric contractions in lower limbs using this device. Due to the novelty of the device design and the method of the delivery, this study initially investigated the effects of different vibration frequencies and amplitudes combined with various effort levels on neuromuscular responses in lower limbs. The results of this study confirm that isometric contraction superimposed on vibration stimulation induce enhanced neuromuscular activity in the lower limbs. The results also confirm that although the neuromuscular responses to vibration depend on multiple factors the main determinants seem to be the vibration frequency, amplitude and muscle contraction /force level. Another limitation of most existing vibration devices is that they are not capable of delivering frequency of the vibration independent of amplitude and vice versa. Further, the evidence suggests that vibration amplitude can play an important role in neuromuscular response to vibration, especially when superimposed with graded contraction/force levels. To address the above limitation, the second aim of this PhD project was to develop and evaluate a prototype miniature upper limb vibration device capable of delivering precise and independent vibration frequency and amplitude stimulation. The miniature upper limb vibration (ULV) device with piezo actuators developed for this thesis, enables precise vibration stimulation to be delivered in a seated position with graded voluntary contraction superimposed. The neuromuscular responses to vibration superimposed on graded isometric contractions in upper limbs were also assessed by investigating the fatiguing effects of superimposed vibration stimulation using this newly developed device. This study is the first to investigate and compare the fatiguing effects of superimposed vibration stimulation pre and postvibration exercise in upper limbs. The results of this study confirm that isometric contraction superimposed on vibration stimulation lead to increased fatigue levels and neuromuscular activity in upper limbs. The results also indicate that post-vibration treatment the muscles display enhanced force generation capability associated with lower fatigue levels. In summary, two (WBV and ULV) novel vibration exercise devices were successfully developed and evaluated for this thesis. The results of the studies on these devices confirm that vibration stimulation superimposed on graded isometric contraction can induce higher neuromuscular activity compared to isometric contraction alone in both upper and lower limbs. However the effects of vibration frequency, amplitude and contraction/force levels seem to differ between the upper and lower limbs.
... Quadriceps performance in terms of functional knee stability is crucial in controlling the body's momentum during landing after a jump or step and plays a major role in sport performance as well as in the control of symptoms in knee osteoarthritis [2, 5]. Quadriceps training improves muscle performance during walking, jumping, and lifting weights [4, 6]. Immobilization and increasing age rapidly reduce muscle force, especially of the quadriceps [7]. ...
Article
Full-text available
Background: The m. quadriceps femoris is the strongest muscle in the human body and plays an important role in sports, activities of daily living and independence. Two older studies showed increased electromyographic (EMG) activity of the quadriceps when the dorsal extensors of the foot were pre-activated. The aim was to physiologically replicate this finding by EMG and to verify it functionally by single leg hop. Methods: EMG activity (root mean square, RMS) was tested on the leg press at the isometric load of the individual 12-repetition-maximum (12RM) weight (on average 79.7 kg) at 45° and 90° knee flexion. Single leg hop distance was measured between the tests. Intra-individual changes between with and without dorsal foot extension were quantified and compared by standardized response means (SRM). Results: Thirty-five healthy subjects between 21 and 57 years were included. The m. vastus medialis was activated on average to an RMS of 32.4 μV without and 53.7 μV with dorsal foot extension (SRM = 1.39, p < 0.001) at 45° knee flexion and an RMS of 124.9 μV versus 152.8 μV (SRM = 1.08, p < 0.001) at 90°. The corresponding data for the rectus femoris were 9.4 μV versus 18.9 μV (SRM = 0.71, p < 0.001) at 45° and 77.8 μV versus 135.3 μV (SRM = 0.89, p < 0.001) at 90°. Mean single leg hop distance was 169.8 cm without versus 178.9 cm with dorsal foot extension (SRM = 1.09, p < 0.001). Conclusions: Pre-activation of dorsal foot extensors significantly increased EMG activity in the m. quadriceps femoris and single leg hop distance. It can therefore be used to improve functional quadriceps muscle performance and knee joint stability in training and rehabilitation.
... A possible explanation might be that exercises on machines contribute to movements made only in a single plane of motion and that ballistic movements are impossible to perform [5,19]. Thus, machine exercises stabilize the environment, tend to facilitate exercise performance, reduce the participation of some synergist muscles, and favor the dominance of quadriceps or hamstring, which negatively affects the knee by increasing strain on the anterior cruciate ligament (ACL) [19][20][21]. Conversely, free-weight exercises constitute compound variable resistance that provides a load which changes to match the ability of the musculoskeletal lever system to produce force throughout the range of motion [22,23]. In addition, free-weight exercises show a more balanced quadriceps-to-hamstrings coactivation ratio by producing a compressive joint load that forces the articular surfaces together, consequently resulting in less anteroposterior displacement of the tibia relative to the femur and minimizing ACL loading [20,24,25]. ...
Article
Introduction. The purpose of this study was to assess the isometric muscle strength (IMS) of the knee extensors and flexors, bilateral asymmetry (BA) and the hamstring: quadriceps ratio (H:Q ratio) between the dominant leg (DL) vs. the non-dominant leg (NDL) of males trained with free-weights vs. machines. Material and Methods: Thirty males were recruited and separated into two groups: Free-weights (n = 15) and Machines (n = 15) groups. All study participants performed the IMS testing for knee extensors and flexors in the DL and NDL using a commercially available load cell. The highest value obtained from the three trials was used for statistical analysis. Results: The IMS of the quadriceps and hamstring muscles for DL and NDL showed a significant increase in the Free-weight group when compared to the Machine group. In addition, a significant difference (p
... This finding is probably because of individual differences in the cross-sectional area of the lean skeletal muscles that reside in the hip region (e.g., gluteus maximus). These muscles are highly activated with lower-body resistance exercises, 1,13,14 which athletes commonly perform. Thus, the leaner athletes in the study may have had greater hip circumferences because of larger hip musculatures even though BF% was low. ...
Article
Purpose: To evaluate the correlations between body adiposity index and other adiposity indexes such as body mass index, hip and waist circumference, waist-to-hip ratio, Σ6 skinfold-thickness and percentage body fat in Colombian elite athletes. Methods: A cross-sectional study was conducted in 149 elite athletes from Colombia (mean age: 26.3 ± 6.5 years; height: 169.2 ± 10.1 cm; body mass: 66.1 ± 12.8 kg; body mass index 22.9 ± 3.0 kg m−1). body adiposity index, body mass index, waist-to-hip ratio, percentage body fat, Σ6 skinfold-thickness and waist circumference were also measured. Results: To select an optimal surrogate for adiposity, we examined the correlation between body adiposity percentage as measured by BIA and several variables, including body adiposity index, body mass index, Σ6 skinfold-thickness, percentage body fat and waist-to-hip ratio. The regression procedure showed that there was a significant relationship between the body adiposity index and BF% (R2 = 0.407, p
... However, reduced effort does not necessarily provide proportional decreases in most of the assessed variables. The results of both simulations and experimental studies have revealed that reduced effort redistributes muscle activity, thus altering the coordination of multijoint tasks and inevitably leading to different directions and magnitudes of changes in the observed mechanical variables (Da Silva, Brentano, Cadore, De Almeida, & Kruel, 2008;Dounskaia & Shimansky, 2016). Despite their extensive use in both research and testing, the same phenomenon has not been studied in maximum vertical jumps. ...
Article
The aim of this study was to evaluate the effect of reduced effort on maximum countermovement jumps. Groups of unskilled and skilled jumpers performed countermovement jumps without an arm swing at 100% and 50% effort. The results revealed markedly reduced jump height and work performed at 50% effort, although the maximum force and power output remained virtually unchanged. The observed differences were consistent across individuals with different jumping skills. A possible cause of differences in changes across the tested variables was a reduced countermovement depth associated with the 50% effort jumps. It is known to cause an increase in maximum force and power outputs, but not in jump height. Therefore, the jump height and work performed may be more closely related to our sense of effort when jumping, rather than our maximum force and power output. From a practical perspective, the present findings reiterate the importance of maximizing effort for making valid assessments of muscle mechanical capacities, as tested by maximal vertical jumps and, possibly, other maximum performance tasks.
... Understanding quadriceps activity during functional tasks may provide valuable insight to clinicians and researchers when evaluating individuals following knee joint injury (Kuenze et al., 2013). Although estimates of quadriceps activation have been performed during closed-chain motor tasks using surface electromyography (Hung and Gross, 1999; Alkner et al., 2000; Earl et al., 2001; Coqueiro et al., 2005; Place et al., 2006; Da Silva et al., 2008; de Ruiter, 2008; Irish et al., 2010), use of the superimposed burst technique in a closed-chain position is a novel approach to assess activation that has yet to be explored in sports medicine research. Therefore, the purpose of this study was to investigate the test–retest reliability and agreement of the superimposed burst technique to measure quadriceps CAR in a closed-chain configuration . ...
... Understanding quadriceps activity during functional tasks may provide valuable insight to clinicians and researchers when evaluating individuals following knee joint injury (Kuenze et al., 2013). Although estimates of quadriceps activation have been performed during closed-chain motor tasks using surface electromyography (Hung and Gross, 1999; Alkner et al., 2000; Earl et al., 2001; Coqueiro et al., 2005; Place et al., 2006; Da Silva et al., 2008; de Ruiter, 2008; Irish et al., 2010), use of the superimposed burst technique in a closed-chain position is a novel approach to assess activation that has yet to be explored in sports medicine research. Therefore, the purpose of this study was to investigate the test–retest reliability and agreement of the superimposed burst technique to measure quadriceps CAR in a closed-chain configuration . ...
Article
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The superimposed burst technique is used to estimate quadriceps central activation ratio during a maximal voluntary isometric contraction, which is calculated from force data during an open-chain knee extension task. Assessing quadriceps activation in a closed-chain position would more closely simulate the action of the quadriceps during activity. Our aim was to determine the test-retest reliability of the quadriceps central activation ratio in the closed chain. Methods Twenty-two healthy, active volunteers (13M/12F; age = 23.8 ± 3; height = 72.7 ± 14.5 cm; mass = 175.3 ± 9.6 kg) were recruited to participate. Knee extension MVIC torque and the peak torque during a superimposed electrical stimulus delivered to the quadriceps during an MVIC were measured to estimate quadriceps CAR. Interclass correlation coefficients were used to assess test-retest reliability between sessions, and Bland-Altman plots to graphically assess agreement between sessions. Results Test-retest reliability was fair for CAR (ICC2,k = 0.68; P = 0.005), with a mean difference of -2.8 ± 10.3%, and limits of agreement ranging -23.1 – 18.1%. Conclusions CAR calculated using the superimposed burst technique is moderately reliable in a closed-chain position using technique-based instruction. Although acceptable reliability was demonstrated, wide limits of agreement suggest high variability between sessions.
... Finally, the modeling work of Dorn et al. (2012) noted significantly greater GMAX (superior, middle, and inferior portions) muscle activity and the subsequent greater GMAX contribution to mechanical work during sprinting compared with slow running. Experimentally, notable GMAX activity is well documented during other activities that involve intense hip extensions such as lunges (Ekstrom et al., 2007), loaded leg presses (Da Silva et al., 2008), squats (Isear et al., 1997; Robertson et al., 2008), stair walking (Lyons et al., 1983; Zimmermann et al., 1994), and throwing (Marzke Oliver and Keeley, 2010). Additionally, we observed significant gluteal activity during ladder climbing. ...
... Finally, the modeling work of Dorn et al. (2012) noted significantly greater GMAX (superior, middle, and inferior portions) muscle activity and the subsequent greater GMAX contribution to mechanical work during sprinting compared with slow running. Experimentally, notable GMAX activity is well documented during other activities that involve intense hip extensions such as lunges (Ekstrom et al., 2007), loaded leg presses (Da Silva et al., 2008), squats (Isear et al., 1997; Robertson et al., 2008), stair walking (Lyons et al., 1983; Zimmermann et al., 1994), and throwing (Marzke Oliver and Keeley, 2010). Additionally, we observed significant gluteal activity during ladder climbing. ...
Article
It has been suggested that the uniquely large gluteus maximus (GMAX) muscles were an important adaptation during hominin evolution based on numerous anatomical differences between humans and extant apes. GMAX electromyographic (EMG) signals have been quantified for numerous individual movements, but not across the range of locomotor gaits and speeds for the same subjects. Thus, comparing relative EMG amplitudes between these activities has not been possible. We assessed the EMG activity of the gluteal muscles during walking, running, sprinting, and climbing. To gain further insight into the function of the gluteal muscles during locomotion, we measured muscle activity during walking and running with external devices that increased or decreased the need to control either forward or backward trunk pitch. We hypothesized that 1) GMAX EMG activity would be greatest during sprinting and climbing and 2) GMAX EMG activity would be modulated in response to altered forward trunk pitch demands during running. We found that GMAX activity in running was greater than walking and similar to climbing. However, the activity during sprinting was much greater than during running. Further, only the inferior portion of the GMAX had a significant change with altered trunk pitch demands, suggesting that the hip extensors have a limited contribution to the control of trunk pitch movements during running. Overall, our data suggest that the large size of the GMAX reflects its multifaceted role during rapid and powerful movements rather than as a specific adaptation for a single submaximal task such as endurance running. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.
... This finding is probably because of individual differences in the cross-sectional area of the lean skeletal muscles that reside in the hip region (e.g., gluteus maximus). These muscles are highly activated with lower-body resistance exercises (5,21), which athletes commonly perform. Thus, the leaner athletes in the study may have had greater hip circumferences because of larger hip musculatures even though BF% was low. ...
Article
The Body Adiposity Index (BAI) is a new, simplistic method for predicting body fat percentage (BF%) via a simple equation of hip circumference to height. Scientific study of this novel method in athletic groups is warranted due to the possibility of it serving as an inexpensive field technique. The purpose of this study was to cross-validate the BAI for predicting BF% in a group of collegiate female athletes by using dual-energy x-ray absorptiometry (DXA) as the criterion variable. Thirty college-age female athletes (age = 20.0 ± 1.3) participated in this study. For each participant, BF% was obtained with the BAI method and compared to DXA. The mean BF% was 27.1 ± 3.4% by the BAI and 26.7 ± 5.9% from DXA, which was not significantly different (p > 0.05). However, the BAI did not provide a significant correlation with the DXA (r = 0.28, R = 0.08, p > 0.05) and resulted in a SEE = 5.78% and TE = 5.84%. Bland-Altman plot showed that the limits of agreement (95% confidence intervals) between the DXA and BAI ranged between -10.2 and 11.8% and there was a significant negative association between the difference and mean of the two methods (r = -0.52, p < 0.01). The results of this investigation indicate that BAI results in large individual errors when predicting BF% in female athletes and has a tendency to provide overestimated values as BF% decreases. Therefore, this method should not be used for predicting individual BF% in athletic women.
... It is important to note that in the knee extension, the VM acts as a synergist with the VL. In this regard, a recent study suggests that quadriceps muscle activity during leg press exercise depends upon and strongly varies with the knee angle, foot placement and effort level (Da Silva et al. 2008). The VM has been shown also to display a nonlinear EMG/force relationship during isometric leg press exercise (Alkner et al. 2000). ...
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Background: Indirect vibration stimulation i.e. whole body vibration or upper limb vibration, has been suggested increasingly as an effective exercise intervention for sports and rehabilitation applications. However, there is a lack of evidence regarding the effects of whole body vibration (WBV) stimulation superimposed to graded isometric contractions superimposed on. For this scope, we investigated the effects of WBV superimposed to graded isometric contractions in the lower limbs on muscle activation. We also assessed the agonist-antagonist co-activation during this type of exercise. Twelve healthy volunteers were exposed to WBV superimposed to graded isometric contractions, at 20, 40, 60, 80 and 100% of the maximum voluntary contractions (V) or just isometric contractions performed on a custom designed horizontal leg press Control (C). Tested stimulation consisted of 30Hzand 50Hz frequencies and 0.5mm and 1.5mm amplitudes. Surface electromyographic activity of Vastus Lateralis (VL), Vastus Medialis (VM) and Biceps Femoris (BF) were measured during V and C conditions. Co-contraction activity of agonist-antagonist muscles was also quantified. The trials were performed in random order. Results: Both the prime mover, (VL) and the antagonist, (BF) displayed significantly higher (P < 0.05) EMG activity with the V than the C condition. For both the VL and BF, the increase in mean EMGrms values depended on the frequency, amplitude and muscle contraction level with 50Hz-0.5mm stimulation inducing the largest neuromuscular activity. 50Hz-0.5mm V condition also led to co-activation ratios significantly (P< 0.05) higher at 40, 80 and 100% of MVC than the C condition. Conclusions: Our results show that the isometric contraction superimposed on vibration stimulation leads to higher neuromuscular activity compared to isometric contraction alone in the lower limbs. Compared to the control condition, the vibratory stimulation leads to higher agonist- antagonist co-activation of the muscles around the knee joint in all vibration conditions and effort levels. The combination of vibration magnitude (frequency and amplitude) and the level of muscle contraction affect neuromuscular activity rather than vibration frequency alone. This results of this study suggest that more parameters need to be taken into consideration when designing vibration exercise programs for sports and rehabilitation purposes.
... Experimentally, notable GMAX activity is well documented during other activities that involve intense hip extensions such as lunges (Ekstrom et al., 2007), loaded leg presses (Da Silva et al., 2008), squats (Isear et al., 1997;Robertson et al., 2008), stair walking (Lyons et al., 1983;Zimmermann et al., 1994), and throwing (Marzke et al., 1988;Oliver and Keeley, 2010). Additionally, we observed significant gluteal activity during ladder climbing. ...
Article
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This paper has been a headache of scientific politics, but we are working on a simple G&P paper to get it out there.
... In this regard, a recent study suggests that quadriceps muscle activity during leg press exercise depends upon and strongly varies with the knee angle, foot placement and effort level. 48 The VM has been shown also to display a non-linear EMG/force relationship during isometric leg press exercise. 49 Further, recent investigation which looked at the ratio of VL/VM contraction during knee extension concluded that the neural drive may be biased towards the VL compared to the VM and seems to be dependent on the force level. ...
Article
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Abstract Background Indirect vibration stimulation, i.e., whole body vibration or upper limb vibration, has been investigated increasingly as an exercise intervention for rehabilitation applications. However, there is a lack of evidence regarding the effects of graded isometric contractions superimposed on whole body vibration stimulation. Hence, the objective of this study was to quantify and analyse the effects of variations in the vibration parameters and contraction levels on the neuromuscular responses to isometric exercise superimposed on whole body vibration stimulation. Methods In this study, we assessed the ‘neuromuscular effects’ of graded isometric contractions, of 20%, 40%, 60%, 80% and 100% of maximum voluntary contraction, superimposed on whole body vibration stimulation (V) and control (C), i.e., no-vibration in 12 healthy volunteers. Vibration stimuli tested were 30 Hz and 50 Hz frequencies and 0.5 mm and 1.5 mm amplitude. Surface electromyographic activity of the vastus lateralis, vastus medialis and biceps femoris were measured during V and C conditions with electromyographic root mean square and electromyographic mean frequency values used to quantify muscle activity and their fatigue levels, respectively. Results Both the prime mover (vastus lateralis) and the antagonist (biceps femoris) displayed significantly higher (P < 0.05) electromyographic activity with the V than the C condition with varying percentage increases in EMG root-mean-square (EMGrms) values ranging from 20% to 200%. For both the vastus lateralis and biceps femoris, the increase in mean EMGrms values depended on the frequency, amplitude and muscle contraction level with 50 Hz–0.5 mm stimulation inducing the largest neuromuscular activity. Conclusions These results show that the isometric contraction superimposed on vibration stimulation leads to higher neuromuscular activity compared to isometric contraction alone in the lower limbs. The combination of the vibration frequency with the amplitude and the muscle tension together grades the final neuromuscular output.
... The SPPB scale (with Cronbach's alpha 0.76) was used to assess the physical performance of the lower extremities, including of three tests: a balance test, walking test and repeated chair stand test [26]. Maximum dominant leg strength was measured through 3 exercises: maximum isotonic knee extension [27], maximum isotonic leg press [28], and maximum isometric knee extension [24]. Maximal isotonic contractions were measured using F&H Fitness Gym machines (F&H Fitness Gym Equipments, Castellón, Spain). ...
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Background: The diagnosis of sarcopenia through clinical assessment has some limitations. The literature advises studies that include objective markers along with clinical assessment in order to improve the sensitivity and specificity of current diagnostic criteria. The decrease of muscle quality precedes the loss of quantity, so we studied the role magnetic resonance imaging biomarkers as indicators of the quantity and quality of muscle in sarcopenia patients. Methods: a cross-sectional analysis was performed to analyze what MR-derived imaging parameters correlate better with sarcopenia diagnostic criteria in women of 70 years of age and over (independent walking and community-dwelling women who were sarcopenic in accordance with EWGSOP criteria with muscle mass adjusted to Spanish population were chosen). Results: The study included 26 women; 81 ± 8 years old. A strong correlation was obtained between cineanthropometric variables (BMI; thigh perimeter and fat mass) and imaging biomarkers (muscle/fat ratio, fatty infiltration, muscle T2*, water diffusion coefficient, and proton density fat fraction) with coefficients around 0.7 (absolute value). Conclusions: Knowing the correlation of clinical parameters and imaging-derived muscle quality indicators can help to identify older women at risk of developing sarcopenia at an early stage. This may allow taking preventive actions to decrease disability, morbidity, and mortality in sarcopenia patients.
... In cases where compressive loading of the spine needs to be minimized, such as with frail individuals and/or those with a history of spinal injury or marked postural deviation, the use of dumbbells and/or kettlebells can be employed during squatting. The leg press is another exercise that also effectively activates the quadriceps and gluteus maximus [26][27][28] , while placing minimal load on the spine. ...
Article
Manipulation of resistance training variables has been shown to have a substantial effect on muscular adaptations. A major variable in this process is exercise selection. In addition to the effectiveness of a given exercise to recruit the target muscle groups, safety considerations and individual comfort during execution of a lift should be considered. The correct biomechanics of the chosen exercise will assist in promoting desired muscle adaptations, while proper safety procedures will reduce risk of injury. Lifting comfort will facilitate enjoyment and foster adherence to the program. Therefore, the purpose of this paper was to offer guidelines for selection of resistance training exercises based on the Efficiency, Safety, and Comfort Analysis Method (ESCAM).
... The leg press is another closed kinetic chain exercise that also effectively activates the quadriceps and gluteus maximus [30][31][32]. Given that the leg press places a minimal load on the spine, it is a suitable alternative for older individuals who are unable to perform squats and their variations and can serve as a springboard for progression to more challenging exercises. ...
Article
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Resistance training has been widely recommended as a strategy to enhance the functional autonomy and quality of life in older individuals. Among the variables that comprise a training session, the selection of exercises stands out as an important consideration for the elderly. Although a wide range of resistance exercise options exists, current guidelines generally do not indicate which exercises should be included and which muscles should be prioritized when prescribing training for older individuals. Therefore, given the lack of evidence-based information on the topic, this paper endeavors to establish recommendations to help guide the prescription of resistance exercises for older adults.
... In contradiction the authors Silva and Chilibeck (21,22) state that when muscle shortening is increased, greater recruitment of motor units occurs to assist the production of maximum force and the greater EMG signal. Our Findings are also in disagreement with the conclusions reached by Maffiuletti et. ...
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The assessment of muscle strength is an important parameter for the performance exam in physiotherapy as it is a mean of diagnosis, prognosis, treatment planning and evaluation of physiotherapeutic interventions. Objective: This study aimed to determine the best hip position to produce the maximum moment of muscle strength and its relationship with the electromyographic (EMG) signal. Participants: The study design included the participation of 30 healthy subjects, corresponding to 60 lower limbs of both sexes, aged between 18 and 22 years without restriction to the practice of physical activity. Methodology: The experimental protocol consisted in gathering surface electromyography information of three portions of the quadriceps muscle and of the peak moment of force during isometric contractions. The task consisted of knee extension in a fixed position of 5° of flexion at three angular positions of the hip, 25°, 55° and 85° against an external resistance offered by isokinetic dynamometer Biodex System 3 Pro. Results / Conclusion: It was found that a greater quadriceps strength is produced at 25° of hip flexion. It was observed that from all portions assessed only the rectus femoris was influenced by the variation of the joint position of the hip, showing a greater EMG signal percentage at 25° of hip flexion. In this position the relationship EMG / force had also higher values.
... However, the disadvantage is that these resistance machines do not require the activation or engagement of any of the important stabilizing muscles. More specifically, leg press is performed using closed-chain kinetic effort [68] while the knee extension involves large lower body muscle groups (i.e., the quadriceps, hamstring) [69]. Consequently, the leg press exercise is widely used for strengthening the lower limbs. ...
Chapter
Aging is associated with a loss of muscle function (i.e., muscle strength and quality) which leads to loss of physical performance and to dependence for activities of daily living. Since muscle strength is the main predictor of physical limitation or adverse outcomes (i.e., frailty, sarcopenia, dementia, mortality), assessing muscle function is useful to prevent these consequences or to rehabilitate it. Consequently, it is important to have objective, reliable, and sensitive tools to assess upper and/or lower limb muscle strength to quantify weakness (identify patient at risk), to prescribe adapted intervention (i.e., physical activity training; nutritional supplementation) to patients’ capacity to counteract functional decline and to follow its impact on aging process. It is also relevant to assess physical performance among older adults since poor physical performance is leading to the same health adverse effects. However, in the literature, a large number of tools, with advantages and disadvantages, are available to assess muscle strength and physical performances. Consequently, clinicians and researchers may have difficulty choosing the most appropriate and/or validated tool for their needs and for older adults. The choice of a tool depends on several criteria such as the objective (i.e., diagnosis), the availability in clinical setting, the need for highly qualified staff, the cost, and the performances (e.g., reliability and reproducibility). Therefore, the aim of the chapter is to summarize the importance of these factors on aging process and the pros and cons of the available tests to assess muscle strength and physical function in clinical and research settings.
... Our main finding is that there was no difference for muscle activation for any muscle analyzed. This agrees with previous findings in upper and lower body muscles [15,16,25,26] and confirms the suggestion that plantar flexors have a great involvement in lower body MJ exercises [28,48]; however, the results were, to some extent, unexpected. ...
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The present study aimed to compare soleus, lateral, and medial gastrocnemius muscles activation during leg press and calf raise exercises in trained men. The study involved 22 trained men (27.1 ± 3.6 years, 82.7 ± 6.6 kg, 177.5 ± 5.2 cm, 3.6 ± 1.4 experience years) who performed one set of each exercise using a 10-repetition maximum (10RM) load in a counterbalanced randomized order and separated by 10 min of rest. The electromyographic signal was measured for the three major plantar flexors: soleus, medial, and lateral gastrocnemius. A comparison between exercises showed that the mean adjusted by peak values during the leg press were 49.20% for the gastrocnemius lateralis, 51.31% for the gastrocnemius medialis, and 50.76% for the soleus. Values for calf raise were 50.70%, 52.19%, and 51.34% for the lateral, medial gastrocnemius, and soleus, respectively. There were no significant differences between exercises for any muscle (lateral gastrocnemius (p = 0.230), medial gastrocnemius (p = 0.668), and soleus (p = 0.535)). The present findings suggest that both leg press and calf raises can be used with the purpose to recruit triceps surae muscles. This bring the suggestion that one can chose between exercises based on personal preferences and practical aspects, without any negative impact on muscle activation.
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The objective of the present study was to evaluate and compare the neuromuscular, morphological and functional adaptations of older women subjected to 3 different types of strength training. 58, healthy women (67±5 year) were randomized to experimental (EG, n=41) and control groups (CG, n=17) during the first 6 weeks when the EG group performed traditional resistance exercise for the lower extremity. Afterwards, EG was divided into three specific strength training groups; a traditional group (TG, n=14), a power group (PG, n=13) that performed the concentric phase of contraction at high speed and a rapid strength group (RG, n=14) that performed a lateral box jump exercise emphasizing the stretch-shortening-cycle (SSC). Subjects trained 2 days per week through the entire 12 weeks. Following 6 weeks of generalized strength training, significant improvements occurred in EG for knee extension one-repetition (1RM) maximum strength (+19%), knee extensor muscle thickness (MT, +15%), maximal muscle activation (+44% average) and onset latency ( - 31% average) for vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) compared to CG (p<0.05). Following 6 more weeks of specific strength training, the 1RM increased significantly and similarly between groups (average of +21%), as did muscle thickness of the VL (+25%), and activation of VL (+44%) and VM (+26%). The onset latency of RF (TG=285±109 ms, PG=252±76 ms, RG=203±43 ms), reaction time (TG=366±99 ms, PG=274±76 ms, RG=201±41 ms), 30-s chair stand (TG=18±3, PG=18±1, RG=21±2) and counter movement jump (TG=8±2 cm, PG=10±3 cm, RG=13±2 cm) was significantly improved only in RG (p<0.05). At the end of training, the rate of force development (RFD) over 150 ms (TG=2.3±9.8 N·s - 1, PG=3.3±3.2 N·s - 1, RG=3.8±6.8 N·s - 1, CG=2.3±7.0 N·s - 1) was significantly greater in RG and PG than in TG and CG (p<0.05). In conclusion, rapid strength training is more effective for the development of rapid force production of muscle than other specific types of strength training and by consequence, better develops the functional capabilities of older women.
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changes negatively aff ect the muscles of the lower limbs, particularly at the knee and ankle [ 6 , 20 ] , leading to impaired mobility and ability to perform activities of daily living (ADL). For example, Skelton et al. showed that aging decreases strength and power capacities and these variables are related to the ability to per-form functional activities like standing and step-ping up [ 48 ] . The impact of aging on the neuromuscular sys-tem diff ers not only in terms of muscle groups and type of contraction studied [ 21 , 29 , 50 ] , but also in the onset latency of muscle activation (OM) [ 37 ] . From a functional and therapeutic perspective, the capacity for the rapid
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The aim of this study was to compare maximal isometric force (MIF) and the electrical activity of the vastus medialis, vastus lateralis, rectus femoris, gluteus maximus and biceps femoris long head muscles between maximal voluntary contractions (MVC) performed at different joint angles, and to identify the most suitable positions to normalize the electromyography (EMG) signals from each of these muscles when they are activated under dynamic conditions. Ten men ranging in age from 20 to 30 years, who were familiar with strength training exercise, were studied. MVC at different joint angles of the knee extensors and flexors (0°, 60°, 90°) and hip extensors (-30°, 0°, 60°) and flexors (90°, 120°) were tested. The MIF values differed significantly between the 60° knee flexion and 60° and 90° knee extension positions (p<0.01). The same was not observed for hip flexion or extension (p>0.05). Significantly higher EMG values were only observed for the rectus femoris muscle at 90° knee extension (p<0.01). No differences between muscles were found for knee flexion, hip flexion or hip extension at the joint angles tested (p>0.05). These results suggest that the 60° knee joint flexion position is the most suitable for assessment of knee extension and flexion MIF, and that all positions tested in this study are suitable for the assessment of hip flexion and extension.
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Objective: To investigate the relationship between strength and electromyographic (EMG) signal in different intensities in the bench press exercise. Methods: Eleven healthy resistance trained men (22.8 ± 3.5) participated into the present study. Maximal isometric strength was determined in the bench press exercise using a load cell. Muscle activation was assessed using surface electromyography (EMG) signals from the muscles pectoralis major, anterior deltoid and posterior deltoid at intensities ranging to 60-90% of maximal voluntary contraction (MVC), in the bench press exercise. This procedure allowed the analysis of the strength/EMG relationship. Results: In all muscles assessed, there were significant differences in the normalized muscle activation between the intensities of 60 and 70% of the MVC, as well as between 70 and 80% (P < 0.05), while there were no differences between 80 and 90% of MVC. In addition, there were significant correlations between strength and EMG signals for the muscles pectoralis major (r = 0.43, P = 0.04), anterior deltoid (r = 0.52, P = 0.01), and posterior deltoid (r = 0.32, P = 0.046). Conclusions: These results suggest that levels of muscle activation near to maximal are obtained at the intensity of 80 of MVC and no additional motor unit recruitment are achieved at 90% of MVC.
Chapter
Sarcopenia is recognized today as a real public health issue. In order to reduce its public health burden, screening for sarcopenia is essential to act early and thus prevent the occurrence of adverse health events. Screening for sarcopenia also avoids the need for unnecessary resource-consuming diagnostic procedures. Several screening tools for sarcopenia exists: the SARC-F questionnaire, the calf circumference, the SARC-F-CalF, the Mini Sarcopenia Risk Assessment, the Ishii score, the equation of Yu, the screening grid of Goodman, the chair and stand test, the finger-ring test, the gripBMI, the Tawaïn Risk Score for sarcopenia, and the red flag method. As the choice of a screening instrument is quite large, it can sometimes be difficult for the clinician to determine which one is the most suitable. Studies have therefore been carried out to compare the performance of different screening tools for sarcopenia. Statistically, the Ishii score offers the best performance (with an area under the curve of 0.914). SARC-F-CalF also exhibits interesting properties. Overall, all of the screening tools for sarcopenia are very effective in detecting the absence of the disease (i.e., high specificity). It is, however, important to remember that the choice of a screening tool is made on the basis of the performance of the tool and also on the basis of other criteria such as its ease of implementation, its reliability, and its acceptability by the population. Therefore, in view of these criteria, the screening tool recommended by scientific societies remains the SARC-F, which is easy to use, reliable, and very well accepted.
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A ordem dos exercícios refere-se à sequência de execução durante uma sessão de treinamento. Evidências demonstram que essa ordem pode afetar o número de repetições realizadas nos exercícios. A percepção subjetiva de esforço (PSE), assim como o número de repetições realizadas, depende da sobrecarga utilizada. Assim, alterações no número de repetições podem afetar a PSE. O volume total de trabalho (VTT) influencia nas adaptações crônicas ao treinamento e também pode ser afetado pela ordem dos exercícios. O objetivo foi verificar o efeito da ordem dos exercícios para membros inferiores no número de repetições realizadas, na PSE e no VTT. Doze homens treinados (19,3 ± 2,1 anos, 71,1 ± 9,8 kg, 172,4 ± 6,1 cm, 23,3 ± 11,5 meses/treino) realizaram duas sessões com os exercícios "leg-press" (L), mesa flexora (F) e cadeira extensora (E) em diferentes ordens (LFE ou EFL). Foram utilizados testes t de "Student" pareados com ajuste de Bonferroni para comparações múltiplas. O número de repetições em L e E diminuiu quando realizados no final da sessão. As repetições realizadas em F diminuíram na LFE. A PSE de E foi maior quando realizada no final da sessão, porém de L e de F não foram afetadas pelas diferentes ordens. O volume de trabalho total de LFE foi maior. Em conclusão, a ordem dos exercícios envolvendo membros inferiores afeta o número de repetições e a PSE de um exercício além do VTT, ressaltando a importância da ordem dos exercícios como uma importante variável na prescrição do treinamento.
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This study investigated the effect of home-based shallow and deep squat trainings on knee extension peak torque, muscle thickness, one-repetition maximum (1RM) leg press, and physical function in older individuals. Sixteen participants were randomly assigned to the shallow squat group (SS group; age, 71.0 ± 4.0 years) or deep squat group (DS group, age; 68.6 ± 3.6 years). Chairs of 40-cm height and chairs with a cushion of 20-cm height (60-cm in total) were used as the depth targets for squats, with participants instructed to sink until their hip touched the chair and cushion. Participants performed four sets of squats per day (35 repetitions per set), three days per week, for 12 weeks at their home. Knee extension peak torque, muscle thickness of quadriceps femoris (e.g., vastus lateralis, rectus femoris, and vastus intermedius), and physical function were measured at weeks 0 (baseline), 4, 8, and 12. Maximal isometric knee extension peak torque, muscle thickness, and walking speed did not change significantly over the 12-week training period in either group ( P > 0.05). However, compared with the baseline, there was significant improvement in the results of 30-s sit-to-stand repetition tests after weeks 8 and 12 in both groups ( P < 0.05). Additionally, 1RM leg press results were significantly improved after weeks 4 and 12 in the DS group, and weeks 4, 8, and 12 in the SS group ( P < 0.05). Results indicate that home-based weight-bearing squat training improves lower limb function in older adults, as well as performance in physical functional tests related to activities of daily living. Moreover, such training benefits older adults regardless of whether squats are shallow or deep.
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Objetivo: Verificar quais métodos de avaliação clínicos de força e potência muscular, e testes de desempenho físico funcionais estão correlacionados com o pico de torque isométrico e dinâmico dos extensores de joelho, e desenvolver equações preditivas que estimem o pico de torque isométrico e dinâmico em pessoas idosas. Métodos: Foram selecionados 49 sujeitos (≥ 60 anos) de ambos os sexos. O pico de torque muscular isométrico (PTISO) e dinâmico concêntrico (PTCON) dos extensores da articulação do joelho do membro preferido foi avaliado através de dinamômetro isocinético no primeiro dia de avaliação. Quarenta e oito horas depois o teste força máxima (1-RM) unilateral do membro preferido foi executado na cadeira extensora, seguindo do teste de potência do membro superior com uma medicine ball de 2 kg (ABM-2). No terceiro dia foram avaliados o teste de equilíbrio dinâmico (time up and go), a capacidade de subir e descer escadas (separadamente), com estes três testes foi construído um índice funcional (IFUNC). Resultados: Os principais resultados demonstraram que o IFUNC não prediz melhoria no pico de torque extensor do joelho (p>0,05). Contrapondo a hipótese inicial que alterações no desempenho do pico de torque, tanto isométrico, como dinâmico, teria uma resposta direta com o desempenho funcional. Conclusão: As medidas de força máxima para membro inferior (cadeira extensora-1-RM) e potência de membro superior (arremesso da bola de medicine ball 2-kg) quando associadas explicam com mais de 60% (p<0,05) uma mudança no desempenho na força isométrica e dinâmica dos extensores de joelho de idosos não treinados. Palavras-chave: Envelhecimento. Músculo esquelético. Dinamômetro de força muscular. Abstract Objective: The aim of the present study was to verify which clinical strength assessment methods and physical functional performance tests are correlated with the isometric and dynamic peak torque of the knee extensors, and to develop predictive equations that estimate the isometric and dynamic peak torque in elderly people. Methods: Forty-nine subjects (≥ 60 years old) of both sexes were selected. The peak isometric torque (PTISO) and concentric dynamic torque (PTCON) of the knee joint extensors on the preferred limb was assessed using an isokinetic dynamometer on the first day of assessment. Forty-eight hours later the unilateral maximum strength test (1-RM) of the preferred limb was performed on the leg extension exercise, followed by the upper limb power test with a 2 kg medicine ball (ABM-2). On the third day, the dynamic balance test (time up and go), the ability to climb and descend stairs (separately) were evaluated, with these three tests a functional index (IFUNC) was built. Results: The main results demonstrated that the IFUNC does not predict improvement in the peak knee extensor torque (p> 0.05). Against the initial hypothesis which improves the performance of peak torque, so much isometric and dynamic, would have a direct response to functional performance. Conclusion: The measures of maximum strength for the lower limb (leg extension, 1-RM) and power of the upper limb (throwing the medicine ball 2-kg) when associated explain more than 60% (p <0.05) changes on performance in the isometric and dynamic strength of knee extensors of untrained elderly.
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The purpose of this study was to examine the recruitment state of synergistic muscles in the thigh muscles in leg press exercise with and without pre-fatigue method using transverse relaxation time (T2) on muscle functional magnetic resonance imaging (MRI). Nine healthy male subjects performed the following two types of exercise trials on separate days: 1) 5 sets of a leg press exercise with pre-fatigue method, which consisted of 3 sets of knee extension exercise (LP-pre), 2) 5 sets of a leg press exercise without pre-fatigue method (LP). Both exercises were performed at a load of 80% one-repetition maximum. Before and immediately after exercise, T2-weighted MR images of right-thigh were taken to calculate T2 values of twelve-thigh muscles. The T2 values for quadriceps femoris muscle and hamstrings in LP increased significantly after the exercise, except in the adductor magnus, adductor longus, gracilis, and sartorius. In contrast, the T2 values for all of the twelve-thigh muscles in LP-pre increased significantly after the exercise. Upon comparison between the two trials, the percentage changes in T2 value for the adductor magnus, adductor longus, and sartorius in LP-pre were found to be significantly greater than those in LP. These results suggest leg press exercise with pre-fatigue method may be effective to increase activity of synergistic muscles in thigh muscles during exercise.
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The purpose of this study was to compare the EMG of the gluteus maximus and biceps femoris between the lunge and the parallel squat. Seven subjects, with experience in strength training, performed eight repetitions of the parallel squat (PS) and the lunge (LU) with an overload corresponding to 50% of body mass. The EMG of the gluteus maximus and biceps femoris was captured, filtered by a forth order Butterworth filter (20-400 Hz) and calculated RMS values. The Wilcoxon Ranked test was used to compare the normalized EMG of each muscle between the two exercises. Both the biceps femoris (p = 0.041) and the gluteus maximus (p = 0.0059) showed increased activation in LU compared to the PS. Despite the moderate activation in both exercises, ranging from 25% to 45%, the myoelectric response of the analyzed muscles was higher, for the participants, in the lunge exercise.
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Objectives: This case report describes in detail the rehabilitation exercise program, provide postoperative therapeutic objectives/recommendations and to facilitate the return to a possible schedule of ADL and participation in sports after the surgical treatment of quadriceps tendon rupture. Also, the exact surgical technique is described. Design: A single case report. Participant: The patient was an active 53-year-old man who sustained this injury as a result of a sudden misstep with his left foot into a hole, while he was trekking across muddy countryside. Clinical examination of the knee revealed skin ecchymosis, swelling and tenderness over the distal thigh. Plain radiographs showed patella baja, and the scheduled magnetic resonance imaging (MRI) showed interrupted continuity of the quadriceps tendon and the patella. A diagnosis of quadriceps tendon rupture was made and the patient was scheduled to undergo surgical intervention the following day. Rehabilitation exercise program: A well-structured rehabilitation exercise program was followed in order to ensure rapid recovery and good functional outcomes. His postoperative course progressed normally, demonstrating a return to the normal activities of daily living at 6 weeks, full active range of motion at 16 weeks, and return to sports recreational activities at 5 months. Conclusions: An early surgical treatment and subsequently a well-structured rehabilitation exercise program have contributed to maximize the functional outcomes of the patient and provide a rapid and safe return to the activities of daily living (7th week) with participation in non-contact sports after the 18th week.
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The purpose of this study was to verify the electromyographic activity of the rectus abdominis and obliquus externus abdominis during abdominal crunch exercise performed with maximum and submaximum loads. Thirteen male and female university students participated in this investigation (18-23 years old). The subjects completed abdominal crunch exercise until exhaustion with 20, 40, 60 and 80% of the maximum load. The root-mean-square (RMS) from electromyography activity of the rectus abdominis and obliquus externus muscles from the first and last three repetitions from each workload performed was analyzed. RMS for the last repetitions increased in relation to the first repetitions for the 20% workload, first two repetitions on 40% workload and first repetition on the 80% workload. There was no difference for the 60% workload. Results showed that external load on abdominal crunch exercise might be an alternative to increase intensity while performing abdominal crunch exercise, which on its turn can be a practical tool for subjects that aim to increase abdominal strength level.
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Resistance-training of the lower limbs can be performed using exercises moving one (single-joint exercises) or several joints (multi-joint exercises). This study compared the effects of training one multi-joint exercise (leg press) or two single-joint exercises (leg extension and kickback) on dynamic and isometric strength and the transferability of dynamic strength between exercises. Fifty-three physically active women were randomized to a multi-joint (MJ) training group (age = 21.95±0.82 years, mass = 64.85±5.76 kg, height = 167.35±2.47 cm; n = 20), single-joint (SJ) training group (age = 22.56±1.66 years, mass = 64.85±5.76 kg, height = 165.94±2.84 cm; n = 18), or a control (CON) group (age = 21.27±0.68 years, mass = 68.43±4.86 kg, height = 168.63±2.84 cm; n = 15). The training groups participated in an 8-week supervised single- or multi-joint lower limb training consisting of 18 sessions. Pre- and post-training, six repetitions maximum (RM) and maximal voluntary isometric contraction in the three exercises were assessed, along with electromyography of the superficial quadriceps muscles. Improvements in all dynamic exercises were greatest after training the specific exercises (ES = 1.26–2.14, P<0.001–0.025) and all were greater in the training groups than in the CON group (ES = 1.43–3.31, P<0.001–0.021). The SJ group improved 6RM in leg extension and kickback more than leg press (ES = 1.51 and 2.04, respectively, P<0.001), whereas the MJ group improved leg press 6RM more than kickback (ES = 1.10, P = 0.002). However, leg press and leg extension strength improved similarly in the MJ group (ES = 0.54, P = 0.072). All strength and electromyographic measures remained unchanged in the CON group (ES = 0.00–0.44, P = 0.412–0.966). Improved dynamic strength in leg press, kickback and leg extension is best attained by training the specific exercises, but both training modalities can improve strength across all exercises.
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OBJECTIVE: To investigate muscle activation of the shoulder extensors and trunk stabilizers by surface electromyography (sEMG) activity during the isometric Ab Wheel Rollout exercise in different shoulder joint positions. METHOD: We recruited 8 young, healthy, resistance trained men (age: 25 ± 3 years, height: 178 ± 5 cm, and total body mass: 81 ± 2 kg). All subjects performed two sets of 10 sec. maximal isometric contractions of the Ab Wheel Rollout exercise keeping the knees fixed on the floor and the arms taut. To perform the exercise, all subjects were randomly assessed in the following three positions related to the angle between the arms and trunk, in random order: arms aligned vertically with the Ab Wheel Rollout exercise (neutral); 90º and 150º. A rest period of 5 minutes was provided between tests. The sEMG signals were recorded in the following muscles: Latissimus Dorsi; Pectoralis Major; Erector Spinae; Rectus Abdominis. RESULTS: There were significant increases in Rectus Abdominis muscle activity between: neutral vs. 90º, neutral vs. 150º and 90º vs. 150º. There was a significant increase in Pectoralis Major muscle activity between neutral x 150º. CONCLUSION: The present findings indicate that (a) Ab Wheel Rollout exercise emphasizes the muscle action of the Pectoralis Major and Rectus Abdominis more than the Latissimus Dorsi and Erector Spinae; (b) the level of muscle activation depends on the external force created by the body mass and lever arm from the center of mass.
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The purpose of this study was to investigate LE muscular strength variables as potential risk factors for all and non‐contact acute knee and ACL injuries in young athletes. A total of 188 young (≤21) male and 174 female basketball and floorball players participated in LE muscular strength tests and were followed up to three years. The strength test battery consisted of 1RM leg press, maximal concentric isokinetic (60°/s) quadriceps and hamstrings and maximal isometric hip abductor strength. The outcomes were a new acute knee or ACL injury and a new acute non‐contact knee or ACL injury. A total of 51 (17 in males and 34 in females) new acute knee injuries registered and 17 (one in males and 16 in females) of these were ACL injuries. In the adjusted Cox regression models, only lower maximal hip abduction strength (kg/kg) was significantly associated with an increased risk of all knee injuries in males (HR 1.80 [95% CI, 1.03‒3.16] for 1 SD decrease in hip abduction). However, ROC curve analysis showed an area under the curve 0.66 revealing that maximal hip abduction strength test cannot be used as a screening tool for an acute knee injury in young male athletes.
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Objectives: To examine the effects of a time saving leg-press training program with moderate vibration on strength parameters, pain, and functional outcomes of patients following total knee arthroplasty in comparison with functional physiotherapy. Design: Randomized controlled trial. Setting: Outpatient Rehabilitation Department at a University Teaching Hospital. Participants: Patients (n=55) with primary total knee arthroplasty (TKA) were randomly allocated into two rehabilitation groups. Interventions: Six weeks after TKA, participants either underwent isokinetic leg-press training combined with moderate vibration (LP, n=26) of 15 minutes duration per session, or functional physiotherapy (PT, n=29) of 30 minutes per session. Both groups received therapy twice a week for a period of 6 weeks. Participants were evaluated at baseline (6 weeks after TKA) and after the 6 weeks rehabilitation program. Main outcome measures: The main outcome measure was maximum voluntary contraction (MVC) of the involved leg. Secondary outcome measures were pain assessed with a visual analogue scale (VAS), range of motion (ROM), stair test (ST), timed up and go test (TUG), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Results: Both groups (LP and PT) showed statistically significant improvements in MVC of knee extensors measured on the knee dynamometer (LP from 0.8 ± 0.06 to 1.0 ± 0.09 Nm/kg BW, PT from 0.7 ± 0.06 to 0.9 ± 0.06 Nm/kg BW, p<.05), and in closed kinetic chain on the leg-press (LP from 8.9 ± 0.77 to 10.3 ± 1.06 N/kg BW, PT from 6.7 ± 0.54 to 9.1 ± 0.70 N/kg BW, p<.05), as well as pain at rest (LP from 2.0 ± 0.36 to 1.3 ± 0.36 VAS and PT from 1.2 ± 0.28 to 1.1 ± 0.31, p<.05), WOMAC and functional measurements after 6 weeks of training. There was no significant difference between the two groups concerning strength, pain, and functional outcomes after training (p>.05). Conclusions: Isokinetic leg-press training with moderate vibration and functional physiotherapy are both effective in regaining muscle strength and function after TKA, however, isokinetic leg-press training is considerably less time consuming.
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The quadriceps muscle supplies the motive force for dynamic knee extension. During this action, the vastus medialis oblique (VMO) and vastus lateralis (VL) co-contract to stabilize the patella as it tracks within the patellofemoral groove. The purpose of this study was to analyze surface electromyographic (SEMG) responses for the VL, VMO, rectus femoris (RF), and biceps femoris (BF), as well as the VMO:VL ratio during an open-kinetic chain 45°angled leg press (LP45). The traditional LP45 technique was compared with 2 alternative LP45 exercise techniques that used a physioball and elastic band, respectively. Thirteen female college students performed 3 protocols in random order: TRAD - 1 LP45 set performed using the traditional exercise technique, PBALL - 1 LP45 set performed with a physioball held between the knee joints, and PEB - 1 LP45 set performed with an elastic band proximal to the knee joints. Ten repetitions at 70% of a 10 repetition maximum load were performed in each protocol, and the SEMG data were recorded for the VMO, VL, RF, and BF muscles. Significant increases in VMO activity were noted during PBALL vs. PEB (p = 0.001) and TRAD (p = 0.002). Higher VMO activity was noted during TRAD vs. PEB (p = 0.001). Greater VL activity was noted during PBALL vs. TRAD (p = 0.0001) and PEB (p = 0.0001). The PBALL condition elicited a greater VMO:VL ratio during the concentric phase vs. the PEB (p = 0.001) and TRAD (p = 0.001) protocols. Greater RF activity was observed during PEB vs. TRAD (p = 0.001) and PBALL (p = 0.001). Therefore, practitioners should consider placing a physioball between the knees during the LP45 exercise as an alternative technique when greater overall quadriceps activity is desired for clinical rehabilitation or a muscle strengthening program.
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The gluteus maximus (GMax) is one of the primary hip extensors. Several exercises have been performed by strength and conditioning practitioners aiming to increase GMax strength and size. This systematic review aimed to describe the GMax activation levels during strength exercises that incorporate hip extension and use of external load. A search of the current literature was performed using PubMed/Medline, SportDiscuss, Scopus, Google Scholar, and Science Direct electronic databases. Sixteen articles met the inclusion criteria and reported muscle activation levels as a percentage of a maximal voluntary isometric contraction (MVIC). The exercises classified as very high level of GMax activation (>60% MVIC) were step-up, lateral step-up, diagonal step-up, cross over step-up, hex bar deadlift, rotational barbell hip thrust, traditional barbell hip thrust, American barbell hip thrust, belt squat, split squat, in-line lunge, traditional lunge, pull barbell hip thrust, modified single-leg squat, conventional deadlift, and band hip thrust. We concluded that several exercises could induce very high levels of GMax activation. The step-up exercise and its variations present the highest levels of GMax activation followed by several loaded exercises and its variations, such as deadlifts, hip thrusts, lunges, and squats. The results of this systematic review may assist practitioners in selecting exercised for strengthening GMax.
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Resistance exercise has been widely recommended for elderly population, since this type of exercise induces important health benefits, especially to improve functional capacity and preserve muscle mass, thus reflecting on the quality of life of older individuals. Among the several components of the resistance exercises the selection of movements to be performed is one of the most important and must be carefully analyzed. Although there may be a wide range of options, the most important recommendations do not specifically indicate the movements that should be included and muscle groups that should be prioritized when prescribing resistance exercise for the elderly. Therefore, considering that there is a lack of information for the Physical Education professional about the topic, this study was developed to support the choices of the movements that will compose the resistance exercise program for the elderly. The study was carried out by compiling and analyzing assumptions and scientific evidences related to resistance exercises and needs of elderly individuals. In conclusion, the choice of movements should be based on the principles of kinesiology, the needs of the elderly, muscle action and exercise safety in order to obtain beneficial results for general health and attenuate possible risks.Keywords: Exercise. Aging. Physical Exertion.ResumoO exercício resistido vem sendo amplamente recomendado para população idosa, uma vez que esse tipo de exercício físico induz a importantes benefícios para saúde; sobretudo, no aprimoramento da capacidade funcional e na preservação da massa muscular, refletindo, desse modo, na qualidade de vida do indivíduo idoso. Dentre os diversos componentes dos exercícios resistidos, a seleção dos movimentos a serem executados é um dos mais importantes e deve ser cuidadosamente analisado. Embora possa existir vasta gama de opções, as principais recomendações não indicam especificamente os movimentos que devem ser incluídos e os grupos musculares que devem ser priorizados nos programas de exercícios resistidos. Portanto, considerando haver uma lacuna de informações sobre o tema, o estudo foi realizado com intuito de subsidiar a seleção dos movimentos que deverão compor os programas de exercícios resistidos para idosos. O estudo foi realizado mediante compilação e análise de pressupostos e evidências científicas referentes aos exercícios resistidos e as necessidades dos idosos. Concluiu-se que a seleção dos movimentos deve ser baseada nos princípios da cinesiologia, nas necessidades dos idosos, na ação muscular e na segurança de execução para se alcançar resultados benéficos para saúde em geral e atenuar possíveis riscos.Palavras-chave: Exercício. Envelhecimento. Esforço Físico.
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Background: A detrimental consequence of diet-induced weight loss, common in athletes who participate in weight cutting sports, is muscle loss. Dietary omega-3 polyunsaturated fatty acids (n-3PUFA) exhibit a protective effect on the loss of muscle tissue during catabolic situations such as injury-simulated leg immobilization. This study aimed to investigate the influence of dietary n-3PUFA supplementation on changes in body composition and muscle strength following short-term diet-induced weight loss in resistance-trained men. Methods: Twenty resistance-trained young (23 ± 1 years) men were randomly assigned to a fish oil group that supplemented their diet with 4 g n-3PUFA, 18 g carbohydrate, and 5 g protein (FO) or placebo group containing an equivalent carbohydrate and protein content (CON) over a 6 week period. During weeks 1–3, participants continued their habitual diet. During week 4, participants received all food items to control energy balance and a macronutrient composition of 50% carbohydrate, 35% fat, and 15% protein. During weeks 5 and 6, participants were fed an energy-restricted diet equivalent to 60% habitual energy intake. Body composition and strength were measured during weeks 1, 4, and 6. Results: The decline in total body mass (FO = −3.0 ± 0.3 kg, CON = −2.6 ± 0.3 kg), fat free mass (FO = −1.4 ± 0.3 kg, CON = −1.2 ± 0.3 kg) and fat mass (FO = −1.4 ± 0.2 kg, CON = −1.3 ± 0.3 kg) following energy restriction was similar between groups (all p > 0.05; d: 0.16–0.39). Non-dominant leg extension 1 RM increased (6.1 ± 3.4%) following energy restriction in FO (p < 0.05, d = 0.29), with no changes observed in CON (p > 0.05, d = 0.05). Dominant leg extension 1 RM tended to increase following energy restriction in FO (p = 0.09, d = 0.29), with no changes in CON (p > 0.05, d = 0.06). Changes in leg press 1 RM, maximum voluntary contraction and muscular endurance following energy restriction were similar between groups (p > 0.05, d = 0.05). Conclusion: Any possible improvements in muscle strength during short-term weight loss with n-3PUFA supplementation are not related to the modulation of FFM in resistance-trained men.
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Background There is convincing evidence for the benefits of resistance training on vertical jump improvements, but little evidence to guide optimal training prescription. The inability to detect small between modality effects may partially reflect the use of ANOVA statistics. This study represents the results of a sub-study from a larger project investigating the effects of two resistance training methods on load carriage running energetics. Bayesian statistics were used to compare the effectiveness of isoinertial resistance against speed-power training to change countermovement jump (CMJ) and squat jump (SJ) height, and joint energetics. Methods Active adults were randomly allocated to either a six-week isoinertial ( n = 16; calf raises, leg press, and lunge), or a speed-power training program ( n = 14; countermovement jumps, hopping, with hip flexor training to target pre-swing running energetics). Primary outcome variables included jump height and joint power. Bayesian mixed modelling and Functional Data Analysis were used, where significance was determined by a non-zero crossing of the 95% Bayesian Credible Interval (CrI). Results The gain in CMJ height after isoinertial training was 1.95 cm (95% CrI [0.85–3.04] cm) greater than the gain after speed-power training, but the gain in SJ height was similar between groups. In the CMJ, isoinertial training produced a larger increase in power absorption at the hip by a mean 0.018% (equivalent to 35 W) (95% CrI [0.007–0.03]), knee by 0.014% (equivalent to 27 W) (95% CrI [0.006–0.02]) and foot by 0.011% (equivalent to 21 W) (95% CrI [0.005–0.02]) compared to speed-power training. Discussion Short-term isoinertial training improved CMJ height more than speed-power training. The principle adaptive difference between training modalities was at the level of hip, knee and foot power absorption.
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Introduction: The purpose of this study was to examine the acute effect of different rest intervals between multiple sets of the 45° angled leg press exercise (LP45) on surface electromyographic (SEMG) spectral and amplitude indices of fatigue. Methods: Fifteen recreationally trained females performed three protocols in a randomized crossover design; each consisting of four sets of 10 repetitions with 1 (P1), 3 (P3), or 5 (P5) minute rest intervals between sets. Each set was performed with 70% of the LP45 ten-repetition maximum load. The SEMG data for biceps femoris (BF), vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles was then evaluated. Results: The SEMG amplitude change in the time coefficient (CRMS) and spectral fatigue index (Cf5) indicated higher levels of fatigue for all muscles evaluated during the P3 protocol versus the P1 and P5 protocols (p ≤ 0.05), respectively. The RF and VL muscles showed greater fatigue levels by the second and third sets; whereas, greater fatigue was shown in the VM and BF muscles by the fourth set (p ≤ 0.05). Conclusions: A three-minute rest interval between sets might represent a neuromuscular window between a fatigue stated and fully recovered state in the context of neural activation. Moreover, a three minute rest interval between sets might allow for consistent recruitment of high threshold motor units over multiple sets, and thus promote a more effective stimulus for strength gains.
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1. Skinfold thickness, body circumferences and body density were measured in samples of 308 and ninety-five adult men ranging in age from 18 to 61 years. 2. Using the sample of 308 men, multiple regression equations were calculated to estimate body density using either the quadratic or log form of the sum of skinfolds, in combination with age, waist and forearm circumference. 3. The multiple correlations for the equations exceeded 0.90 with standard errors of approximately ±0.0073 g/ml. 4. The regression equations were cross validated on the second sample of ninety-five men. The correlations between predicted and laboratory-determined body density exceeded 0.90 with standard errors of approximately 0.0077 g/ml. 5. The regression equations were shown to be valid for adult men varying in age and fatness.
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Single fibers from the tibialis anterior muscle of Rana temporaria at 0.8-3.8 degrees C were subjected to long tetani lasting up to 8 s. Stretch of the fiber early in the tetanus caused an enhancement of force above the isometric control level which decayed only slowly and stayed higher throughout the contraction. This residual enhancement was uninfluenced by velocity of stretch and occurred only on the descending limb of the length-tension curve. The absolute magnitude of the effect increased with sarcomere length to a maximum at approximately 2.9 micrometers and then declined. The phenomenon was further characterized by its dependence on the amplitude of stretch. The final force level reached after stretch was usually higher than the isometric force level corresponding to the starting length of the stretch. The possibility that the phenomenon was caused by nonuniformity of sarcomere length along the fiber was examined by (a) laser diffraction studies that showed sarcomere stretch at all locations and (b) studies of 9-10 segments of approximately 0.6-0.7 mm along the entire fiber, which all elongated during stretch. Length-clamped segments showed residual force enhancement after stretch when compared with the tetanus produced by the same segment held at the short length as well as at the long length. It is concluded that residual force enhancement after stretch is a property shown by all individual segments along the fiber.
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Altering foot stance is often prescribed as a method of isolating muscles during the parallel squat. The purpose of this study was to compare activity in six muscles crossing the hip and/or knee joints when the parallel squat is performed with different stances and bar loads. Nine male lifters served as subjects. Within 7 d of determining IRM on the squat with shoulder width stance, surface EMG data were collected (800 Hz) from the rectus femoris, vastus medialis, vastus lateralis, adductor longus, gluteus maximus, and biceps femoris while subjects completed five nonconsecutive reps of the squat using shoulder width, narrow (75% shoulder width), and wide (140% shoulder width) stances with low and high loads (60% and 75% 1RM, respectively). Rep time was controlled. A goniometer on the right knee was used to identify descent and ascent phases. Integrated EMG values were calculated for each muscle during phases of each rep, and the 5-rep means for each subject were used in a repeated measures ANOVA (phase x load x stance, alpha = 0.05). For rectus femoris, vastus medialis, and vastus lateralis, only the load effect was significant. Adductor longus exhibited a stance by phase interaction and a load effect. Gluteus maximus exhibited a load by stance interaction and a phase effect. Biceps femoris activity was highest during the ascent phase. The results suggest that stance width does not cause isolation within the quadriceps but does influence muscle activity on the medial thigh and buttocks.
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The purpose of this study was to assess the effects of contraction intensity, gender, and muscle on median frequency of the three superficial portions of the quadriceps femoris muscle. Thirty healthy volunteers were assessed for isometric electromyogram activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles with the knee at 60 degrees flexion. Subjects performed 5-s isometric contractions at 10, 20, 30, 40, 50, 60, 70, 80, and 90% of the average of three maximal voluntary contractions. Median frequency (f(med)) of the three muscles was assessed through a power spectral analysis performed over 11 consecutive 512-ms epochs overlapping each other by one-half their length. The f(med) for each of the 11 epochs was then determined, followed by calculation of the mean and SD. The major findings of this study demonstrated that overall f(med) was significantly highest for the VL and lowest for the VM, whereas RF f(med) was between that of the other two muscles. Similar findings were observed for f(med) variability as the VL was significantly higher than the VM and RF, with no gender differences or differences between the latter two muscles. The results demonstrate that the largest change in f(med) as a function of contraction intensity occurred for the VL in men (18.6%) and women (7.6%). These findings suggest that muscle fiber-type homogeneity may exist in the VM and RF, which displayed negligible changes in f(med), whereas the VL may possess greater morphological variability.
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This study determined the effects of a short period of knee isometric training on the quadriceps muscles accessible to surface electromyography (EMG). For this purpose, a training (n = 9) and a control (n = 7) group were tested on five identical occasions at 1 week intervals during 4 weeks. The training group exercised three times a week by making isometric knee extensions at 80% of the maximal voluntary contraction (MVC). During the test sessions, maximal and submaximal torque and associated activations of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) muscles were analysed. As a result of training, differences between MVC values of the two groups were highly significant (P<0.001), whereas only RF-EMG showed significant differences (P<0.05). The VL and VM did not present any significant changes in maximal activation. The EMG torque relationships were analysed individually before and after the training period. For the control subjects, EMG-torque relationships did not present significant changes while for the training group, these relationships showed a significant increase in RF, VL, and VM maximal activation in 6, 6 and 4 subjects, respectively, and a significant decrease in 1, 2 and 5 subjects, respectively. In almost all cases, a significant downward shift of the relationship was observed. This study confirmed that the parts of the quadriceps muscle tested present different adaptation capacities and demonstrate inter-individual variability in the strategies used to enhance muscle strength. In conclusion, to analyse the neural effects resulting from training in a large and compartmentalized muscle like the quadriceps femoris, it is desirable to take into account each muscle independently. Moreover, we suggest that overall results obtained from the experiment population should be completed by an analysis on individuals.
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The aim of this study was to quantify and compare mean quadriceps muscle activity and applied load for eight seated quadriceps exercises using four types of resistance. Using surface electromyography (EMG), the right rectus femoris (RF), vastus lateralis (VL), and vastus medialis oblique (VMO) muscles of 52 university students aged 23.5 +/- 3.4 yr (35 female and 17 male subjects) were examined during the exercises. Resistance devices included an ankle weight (78 N), blue Thera-Band tubing, a Cybex 340 isokinetic dynamometer, and an Inertial Exercise Trainer (IET). Electrogoniometer data were collected to determine the range of motion (ROM), angular velocity, and phase (concentric/eccentric) of exercise. Load cell data were analyzed to determine tubing and IET applied loads during exercise. A within-subjects criterion was used to improve intrasubject EMG reliability. All EMG values were normalized to a 100% maximum voluntary isometric contraction. Repeated measures ANOVAs with Bonferroni comparisons were used for statistical analysis. Within-subject effects of muscle and exercise were significant (P < 0.05) for both the concentric and eccentric muscle activity. The interaction effect of mean average EMG amplitude across exercises for the concentric phases of knee extension was significant (P = 0.001). No significant interactions were found for the eccentric phases of all seated quadriceps exercises. None of the exercises selectively isolated the VMO over the VL; however, the VMO/VL ratio was less (P < 0.05) during the concentric phases of the free weight and elastic tubing exercise when compared with the others. Eccentric phase VMO/VL ratios revealed that inertial resistance elicited greater muscle activity than other forms of resistance exercise. These findings suggest clinicians should consider biomechanical and resistance data when developing a strengthening program for the quadriceps muscle. Some seated quadriceps exercises may be more appropriate for certain rehabilitation goals than others.
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The aim of this work is to provide information about the degree of inter-subject uniformity of location of innervation zone (IZ) in 13 superficial muscles of the lower limb. The availability of such information will allow researchers to standardize and optimize their electrode positioning procedure and to obtain accurate and repeatable estimates of surface electromyography (sEMG) signal amplitude, spectral variables and muscle fiber conduction velocity. Surface EMG signals from gluteus maximus, gluteus medius, tensor faciae latae, biceps femoris, semitendinosus, vastus medialis obliquus, vastus lateralis, rectus femoris, tibialis anterior, peroneus longus, soleus, gastrocnemius medialis and lateralis muscles of ten healthy male subjects aged between 25 and 34 years (average = 29.2 years, S.D. = 2.5 years) were recorded to assess individual IZ location and signal quality. Tensor faciae latae, biceps femoris, semitendinosus, vastus lateralis, gastrocnemius medialis and lateralis showed a high level of both signal quality and IZ location uniformity. In contrast, rectus femoris, gluteus medius and peroneus longus were found to show poor results for both indexes. Gluteus maximus, vastus medialis obliquus and tibialis anterior were found to show high signal quality but low IZ location uniformity. Finally, soleus muscle was found to show low signal quality but high IZ location uniformity. This study identifies optimal electrode sites for muscles in the lower extremity by providing a standard landmarking technique for the localization of the IZ of each muscle so that surface EMG electrodes can be properly positioned between the IZ and a tendon.
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Determination of individual maximum voluntary contraction (MVC) force is used as the gold standard for normalising surface EMG (SEMG) data. Assuming a linear amplitude-force relationship, individual strain levels are defined according to percentage rates of the measured MVC levels. The purpose of the study was to investigate if the assumed force-strain relationship can be applied without qualification. Therefore, healthy volunteers (nine men, ten women) were investigated during isometric exercises of shoulder muscles at MVC and 50% levels. Tasks were performed at four different angular positions in frontal, sagittal and horizontal planes. In each plane, both possible force directions were investigated. SEMG was taken simultaneously from 13 muscles of the shoulder and upper arms from both sides of the body. At a force level of 50% MVC, SEMG amplitude levels were compared to the expected 50% level. Differences in muscular co-ordination patterns were also determined. During retroversion and horizontal flexion, amplitude levels significantly remained at levels below 50%. This was seen for all the muscles investigated, independent of relative contribution to force production. During horizontal extension and abduction, the main force-producing muscles showed amplitude levels that significantly exceeded the expected 50% level. Co-ordination patterns differed significantly between MVC and submaximal conditions for anteversion, retroversion and horizontal extension. Specifically, four shoulder muscles showed higher proportions at the 50% level compared to MVC. Therefore, certain percentage rates of MVC force levels exhibit quite different strain rates, as identified by SEMG. Depending on force direction, differences in co-ordination patterns exist between MVC and submaximal test conditions. Both findings have implications for therapeutic and training applications.
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A repeated-measures, counterbalanced design. To test whether subjects could learn and retain the ability to alter the relative activity of abdominal muscle groups when performing trunk curl exercises. Although trunk curl exercises are widely prescribed, a disadvantage of trunk curls is that they primarily activate rectus abdominis, while the internal and external oblique abdominis muscles are considered to be more important contributors to lumbar stability. A convenience sample of 25 subjects performed trunk curl exercises in accordance with 3 different sets of instructions: nonspecific instructions (NS), instructions intended to emphasize rectus abdominis activity (RE), and instructions intended to emphasize oblique abdominis activity (OE). Electromyographic (EMG) activity was recorded from the upper and lower rectus and the internal and external oblique abdominis muscles while a physical target was used to insure that the trunk was raised to the same height for all conditions. Normalized root-mean-square EMG amplitude measures were used to test for instruction-dependent changes in the relative EMG activity of the rectus and oblique muscle groups. Following a single, brief, instruction session, subjects performing trunk curls had significantly greater normalized oblique:rectus EMG ratios when following OE instructions (mean [+/- SD] oblique-rectus ratio, 1.45 +/- 0.34) than when following RE (mean [+/- SD] oblique-rectus ratio, 0.76 +/- 0.24) or NS (mean [ISD] oblique-rectus ratio, 0.63 +/- 0.23) instructions. Retesting 1 week later indicated that subjects retained this skill. With minimal instruction, subjects are able to volitionally alter the relative activity of the oblique and rectus abdominis muscles when performing trunk curls. Incorporating instructions emphasizing oblique abdominis activity into lumbar stabilization programs appears promising and has potential advantages over other approaches to altering abdominal muscle activity during trunk
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This lecture explores the various uses of surface electromyography in the field of biomechanics. Three groups of applications are considered: those involving the activation timing of muscles, the force/EMG signal relationship, and the use of the EMG signal as a fatigue index. Technical considerations for recording the EMG signal with maximal fidelity are reviewed, and a compendium of all known factors that affect the information contained in the EMG signal is presented. Questions are posed to guide the practitioner in the proper use of surface electromyography. Sixteen recommendations are made regarding the proper detection, analysis, and interpretation of the EMG signal and measured force. Sixteen outstanding problems that present the greatest challenges to the advancement of surface electromyography are put forward for consideration. Finally, a plea is made for arriving at an international agreement on procedures commonly used in electromyography and biomechanics.
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Traditionally, the two-headed gastrocnemius muscle has been considered as one muscle. The purpose of this study was to delineate if electromyographic (EMG) activity differences existed between the medial and lateral gastrocnemius heads, as well as torque output, in the normal right leg, during isometric plantar flexion contractions at three knee angles. Thirty volunteers, between the ages of 18-35, participated in this study. Isometric plantar flexion, with the ankle at 90°, was performed at three knee angles; 0°, 45°, and 90°. The EMG activity was measured in root-mean-square (RMS) microvolts on the Bioscope electromyographic feedback unit, and torque output was measured on the Biodex System II Dynamometer. Results showed decreasing EMG activity of both the medial and lateral gastrocnemius heads as the knee angle changed from 0°to 90°. EMG output decreased significantly as knee flexion increased from 0°to 45°to 90°(F = 14.29, P = 0.0007). However, the pattern of EMG activity decline for medial and lateral gastrocnemius heads was significantly different (F = 4.58, P = 0.0143). Plantar flexion torque decreased significantly across the three angles (F = 94.64, P = 0.0001). It appears that the length-tension principle played a major role in the declining EMG and torque, during isometric plantar flexion. The differences of the medial and lateral gastrocnemius pattern of decline implies that the two heads of the gastrocnemius muscle should be considered as separate entities. However, many factors not controlled for in this study, may have impacted the results. Therefore, health professionals should look at this study as a preliminary study in the investigation of the activation of the medial and lateral gastrocnemius muscles, leading to further investigation.
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Samples of skeletal muscle were taken from 50 sites in each of 6 previously normal male autopsy subjects aged between 17 and 30 years. The respective percentages of Type I and Type II fibres were calculated and showed that there was a wide variation in fibre type proportions between the 6 samples in almost all the muscles studied. Examination of the mean fibre type proportions of each muscle revealed that predominantly tonic muscles had a high percentage of Type I fibres and predominantly phasic muscles had a high percentage of Type II fibres. Most of the muscles studied were known to fulfil both tonic and phasic functions, however, and showed no striking preponderance of either fibre type.The spatial distribution of the fibre types was examined in order to determine whether this was random or not. The number of “enclosed” fibres observed in the actual samples was compared statistically with the number expected to occur in a hexagonal lattice model, assuming a random distribution. In the great majority of muscles, the distribution of the fibre types was in fact random, though isolated instances of grouping of fibres of uniform type were noted in some distal muscles and more regularly in extensor digitorum brevis.The methods used in the quantitative assessment of the proportions and spatial distribution of the respective fibre types in normal muscle have obvious applications in the study of neuromuscular disease.
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The purpose of this study was to determine the relationship between motor unit recruitment within two areas of the pectoralis major and two forms of bench press exercise. Fifteen young men experienced in weight lifting completed 6 repetitions of the bench press at incline and decline angles of +30 and -15[degrees] from horizontal, respectively. Electrodes were placed over the pectoralis major at the 2nd and 5th intercostal spaces, midclavicular line. Surface electromyography was recorded and integrated during the concentric (Con) and eccentric (Ecc) phases of each repetition. Reliability of IEMG across repetitions was r = 0.87. Dependent means t-tests were used to examine motor unit activation for the lower (incline vs. decline) and upper pectoral muscles. Results showed significantly greater lower pectoral Con activation during decline bench press. The same result was seen during the Ecc phase. No significant differences were seen in upper pectoral activation between incline and decline bench press. It is concluded there are variations in the activation of the lower pectoralis major with regard to the angle of bench press, while the upper pectoral portion is unchanged. (C) 1997 National Strength and Conditioning Association
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The seated knee extension is commonly used with the parallel squat to promote balance between the vastus medialis (VM) and vastus lateralis (VL). No controlled studies have examined the relative contributions of each muscle during these exercises, so this study employed EMG analysis to determine their contributions. Ten experienced lifters performed squats and knee extensions at their 10-RM. Sets were separated by 15 min rest and the order of performance was reversed between sessions, which were 1 week apart. EMG was collected on the VL and VM of the dominant leg during the first and last repetition of each exercise. Since EMG activity differed significantly between the two testing days, each was analyzed separately. No significant differences were found between the root mean square of the amplitude of the EMG for the VL and VM during either exercise. The parallel squat elicited more electrical activity than the knee extension in both muscles, and the downward shift in frequency of the EMG signal was greater for both the VM and VL during the parallel squat. The results question the value of the knee extension as a supplemental exercise in this case. (C) 1994 National Strength and Conditioning Association
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To compare the effectiveness of 3 weight-training movements for the hamstrings, 11 weight-trained men performed 3 repetitions at 75% of 1 repetition maximum of the leg curl (LC), stiff-leg deadlift (SLDL), and back squat. Integrated electromyography (EMG) and peak EMG were analyzed in the biceps femoris and semitendinosus independantly during the concentric (CON) and eccentric (ECC) phase of each exercise. Results were as follows: CON-LC and CON-SLDL elicited the greatest integrated EMG activity, with no significant difference between exercises. The CON-squat showed approximately half as much integrated EMG activity as CON-LC and CON-SLDL. Highest peak EMG was found in the CON-LC and CON-SLDL, with no significant difference in these exercises. The CON-squat produced a peak EMG that was approximately 70% of LC and SLDL. We conclude that LC and SLDL involve the hamstrings to a similar degree; however, the back squat involves only about half as much hamstring integrated EMG activity as LC and SLDL. (C) 1999 National Strength and Conditioning Association
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Single fibres from the semitendinosus muscle of Rana temporaria were stretched during fused tetanic contractions and tension and sarcomere length (laser diffraction) responses were recorded. Stretch to the fibres caused proportional increase in length of the sarcomeres. The force increased to a plateau value which was maintained during stretch or increased slightly. The plateau value of force during stretch was dependent upon the velocity of stretch, was independent of the amplitude of stretch and was not proportional to overlap of thick and thin filaments. There was enhancement of force after stretch compared with that produced at the same sarcomere length during isometric tetani. This force enhancement was independent of the velocity at which the stretch had been applied. At sarcomere lengths between 1.9 and 2.3 μm, the force enhancement after stretch decayed rapidly, was independent of amplitude of stretch above approximately 25 nm per sarcomere and was not associated with a shift of the force-velocity curve. At sarcomere lengths above 2.3 μm the force enhancement after stretch decayed very slowly and was still present after 4 sec in long tetani. At sarcomere lengths above 2.3 μm, force enhancement after stretch increased with amplitude of stretch and increased for any given stretch amplitude with sarcomere length. The force recorded after stretch was thus not proportional to overlap of thick and thin filaments. At sarcomere lengths above 2.3 μm, the force enhancement after stretch was associated with a shift towards higher force values of the force-velocity curve. The velocity of shortening at zero load (V(max)) derived by hyperbolic extrapolation of the force-velocity curve was not affected. Tension enhancement during and after stretch has a stabilizing effect in preventing dispersion of sarcomere length, particularly on the descending limb of the length-tension curve.
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An analytic study was initiated to investigate whether the normalized surface myoelectric signal vs. normalized force relationship varies in different human muscles and whether it is dependent on training level and rate of force production. The data were obtained from experiments that involved the biceps, deltoid, and first dorsal interosseous of three pianists, four long-distance swimmers, three power lifters, and six normal subjects. The elite performers (among the world's best) were chosen because they exhibited varying degrees of fine motor control, endurance training, and power training in different muscles. Approximately 200 isometric linearly force-varying contractions peaking at 80% of the maximal voluntary contraction level were processed. The results indicated that the myoelectric signal-force relationship was primarily determined by the muscle under investigation and was generally independent of the subject group and the force rate. Whereas this relationship was quasilinear for the first dorsal interosseous, it was nonlinear for the biceps and deltoid. Several possible physiological causes of the observed behavior of the myoelectric signal-force relationship are discussed.
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Previous research with women has shown that body composition regression equations derived from anthropometric variables were population specific. This study sought to derive generalized equations for women differing in age and body composition. The hydrostatic method was used to determine body density (BD) and percent fat (%F) on 249 women in 18 to 55 years (X = 31.4 +/- 10.8 yrs) and 4 to 44 %F (X = 24.1 +/-7.2 %F). Skinfold fat (S), gluteal circumference (C) and age were independent variables. The quadratic form of the sum of three, four and seven S in combination with age and gluteal C produced multiple correlations that ranged from 0.842 to 0.867 with standard errors of 3.6 to 3.8 %F. The equations were cross-validated on a different sample of 82 women with similar age and %F characteristics. The correlations between predicted and hydrostatically determined %F ranged from 0.815 to 0.820 with standard errors of 3.7 to 4.0 %F. This study showed that valid generalized body composition equations could be derived for women varying in age and body composition, but care need to be exercised with women over an age of forty.
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During an unloaded squat, hamstring and quadriceps co-contraction has been documented and explained via a co-contraction hypothesis. This hypothesis suggests that the hamstrings provide a stabilizing force at the knee by producing a posteriorly-directed force on the tibia to counteract the anterior tibial force imparted by the quadriceps. Research support for this hypothesis, however, is equivocal. Therefore, the purposes of this study were 1) to determine muscle recruitment patterns of the gluteus maximus, hamstrings, quadriceps, and gastrocnemius during an unloaded squat exercise via EMG and 2) to describe the amount of hamstring-quadriceps co-contraction during an unloaded squat. Surface electrodes were used to monitor the EMG activity of six muscles of 41 healthy subjects during an unloaded squat. Each subject performed three 4-s maximal voluntary isometric contractions (MVIC) for each of the six muscles. Electrogoniometers were applied to the knee and hip to monitor joint angles, and each subject performed three series of four complete squats in cadence with a metronome (50 beats.min-1). Each squat consisted of a 1.2-s eccentric, hold, and concentric phase. A two-way repeated measures ANOVA (6 muscles x 7 arcs) was used to compare normalized EMG (percent MVIC) values during each arc of motion (0-30 degrees, 30-60 degrees, 60-90 degrees, hold, 90-60 degrees, 60-30 degrees, 30-0 degrees) of the squat. Tukey post-hoc analyses were used to quantify and interpret the significant two-way interactions. Results revealed minimal hamstring activity (4-12% MVIC) as compared with quadriceps activity (VMO: 22-68%, VL: 21-63% of MVIC) during an unloaded squat in healthy subjects. This low level of hamstring EMG activity was interpreted to reflect the low demand placed on the hamstring muscles to counter anterior shear forces acting at the proximal tibia.
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Little research is available on the muscle activity patterns of the lower extremity muscles during dynamic closed chain squatting activities. The purpose of this study was to examine the effect of lower extremity position during an Olympic squat on the muscle activity patterns of the vastus medialis, vastus lateralis, semimembranosus/semitendinosus, and biceps femoris. Twenty-five healthy, untrained subjects, 18-35 years old, were randomly assigned initial squatting positions of either self-selected neutral or 30 degrees of lower extremity turn-out from the self-selected neutral position. Surface electromyography and motion analysis data were collected simultaneously in 10 degrees intervals and analyzed from 10-60 degrees of knee flexion in both the ascending and descending phases of the squat. A four-way analysis of variance indicated that the main effect of lower extremity position and the interaction of extremity position and knee joint angles were not found to cause significant changes in muscle activity patterns. Significant changes in muscle activity did occur with changes in knee flexion angles in the vastus medialis and vastus lateralis but not in the semimembranosus/semitendinosus or biceps femoris.
Article
Although closed (CKCE) and open (OKCE) kinetic chain exercises are used in athletic training and clinical environments, few studies have compared knee joint biomechanics while these exercises are performed dynamically. The purpose of this study was to quantify knee forces and muscle activity in CKCE (squat and leg press) and OKCE (knee extension). Ten male subjects performed three repetitions of each exercise at their 12-repetition maximum. Kinematic, kinetic, and electromyographic data were calculated using video cameras (60 Hz), force transducers (960 Hz), and EMG (960 Hz). Mathematical muscle modeling and optimization techniques were employed to estimate internal muscle forces. Overall, the squat generated approximately twice as much hamstring activity as the leg press and knee extensions. Quadriceps muscle activity was greatest in CKCE when the knee was near full flexion and in OKCE when the knee was near full extension. OKCE produced more rectus femoris activity while CKCE produced more vasti muscle activity. Tibiofemoral compressive force was greatest in CKCE near full flexion and in OKCE near full extension. Peak tension in the posterior cruciate ligament was approximately twice as great in CKCE, and increased with knee flexion. Tension in the anterior cruciate ligament was present only in OKCE, and occurred near full extension. Patellofemoral compressive force was greatest in CKCE near full flexion and in the mid-range of the knee extending phase in OKCE. An understanding of these results can help in choosing appropriate exercises for rehabilitation and training.
Article
The purpose of this study was to compare mean integrated electromyographic values (EMG(int)) during biomechanically comparable closed kinetic chain/fixed external load, open kinetic chain/moveable no load, and moveable external load exercises. EMG(int) were obtained for the pectoralis major (PM) and the long head of the triceps (T) during absorption and force phases of three biomechanically comparable exercises: the push-up (PU); the bench press-load (BP-L); and the bench press-no load (BP-NL) equated to the closed kinetic chain/fixed external load; moveable external load; and open kinetic chain/moveable no load conditions respectively. A force plate was used to equate load for the PU and BP-L exercises. Ten males (24+/-4.4 yr) participated in the three randomly ordered exercises. A pronated, closed grip was used for all exercises. The mean integrated EMG values from three isometric maximal voluntary contractions were used to determine a reference EMG (EMG(MVC)) for each muscle. Normalized EMG values (NEMG) were determined by EMG(int)/EMG(Mvc) and analyzed by one-factor repeated measures ANOVA for each muscle (PM and T) during each phase (absorption and force). There was no significant difference (P > 0.05) between the equivalently loaded, different boundary exercises (PU and BP). Statistical significance (P < 0.05) was determined between the differently loaded, equivalent boundary exercises (BP and BP-NL) as well as the differently loaded, different boundary exercises (PU and BP-NL). Results from this study support the theory that activities of similar biomechanical motions and mass of loading, regardless of the boundary condition, have comparable EMG values of primary muscle groups. In addition, this study suggests external load is more important than boundary condition in describing human activity.
Article
Because a strong and stable knee is paramount to an athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise. Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation. Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60 degrees knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50 degrees knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100 degrees knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee. The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.
It was studied the trapezius muscle and serratus anterior muscle in 24 male volunteers using a 2-channel TECA TE 4 electromyograph and Hewlett Packard surface electrodes, during the execution of four different modalities of military press exercises with open grip. The results showed that TS acted significantly in the modalities standing and sitting press behind neck, while SI acted in all the modalities, i.e., standing and sitting press behind neck and forward, justifying their inclusion as basic exercises for physical conditioning programmes.
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The specific aim of this project was to quantify knee forces and muscle activity while performing squat and leg press exercises with technique variations. Ten experienced male lifters performed the squat, a high foot placement leg press (LPH), and a low foot placement leg press (LPL) employing a wide stance (WS), narrow stance (NS), and two foot angle positions (feet straight and feet turned out 30 degrees ). No differences were found in muscle activity or knee forces between foot angle variations. The squat generated greater quadriceps and hamstrings activity than the LPH and LPL, the WS-LPH generated greater hamstrings activity than the NS-LPH, whereas the NS squat produced greater gastrocnemius activity than the WS squat. No ACL forces were produced for any exercise variation. Tibiofemoral (TF) compressive forces, PCL tensile forces, and patellofemoral (PF) compressive forces were generally greater in the squat than the LPH and LPL, and there were no differences in knee forces between the LPH and LPL. For all exercises, the WS generated greater PCL tensile forces than the NS, the NS produced greater TF and PF compressive forces than the WS during the LPH and LPL, whereas the WS generated greater TF and PF compressive forces than the NS during the squat. For all exercises, muscle activity and knee forces were generally greater in the knee extending phase than the knee flexing phase. The greater muscle activity and knee forces in the squat compared with the LPL and LPH implies the squat may be more effective in muscle development but should be used cautiously in those with PCL and PF disorders, especially at greater knee flexion angles. Because all forces increased with knee flexion, training within the functional 0-50 degrees range may be efficacious for those whose goal is to minimize knee forces. The lack of ACL forces implies that all exercises may be effective during ACL rehabilitation.
Article
The purpose of this study was to compare the number of testing sessions required to achieve consistent 1 repetition maximum (1RM) strength measurements in untrained old and young women. Consistency of measurement was defined as consecutive 1 RM strength measures that increased by 1 kg or less. Untrained old (n = 6, age 66 +/- 5 years) and untrained young (n = 7, age 23 +/- 4 years) women were repeatedly strength-tested for bilateral concentric knee extension 1 RM strength until consecutive measurements were increased by no more than 1 kg. At least 48 hours of rest was allowed between 1 RM measurements. The old subjects required significantly more testing sessions (8-9 sessions) compared with the young subjects (3-4 sessions) to achieve the same absolute consistency of measurement (p < 0.05). Absolute increase in strength between the first and final testing sessions did not differ between groups (young = 11 +/- 4 kg and old = 13 +/- 2 kg) (p > 0.05). The relative increase was significantly greater in the older subjects (young = 12 +/- 5%; old = 22 +/- 4%) (p < 0.05). In conclusion, older subjects require more practice and familiarization and show greater relative increases in 1RM strength when compared with younger subjects of the same experience level. This is important to consider, especially when evaluating the magnitude of strength increase in response to resistance training.