Article

Walking and Running Require Greater Effort from Ankle than Knee Extensor Muscles

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Abstract

Introduction: The knee and ankle extensors as human primary antigravity muscle groups are of utmost importance in a wide range of locomotor activities. Yet, we know surprisingly little about how these muscle groups work, and specifically, how close to their maximal capacities they function across different modes and intensity of locomotion. Therefore, to advance our understanding of locomotor constraints, we determined and compared relative operating efforts of the knee and ankle extensors during walking, running and sprinting. Methods: Using an inverse dynamics biomechanical analysis, the muscle forces of the knee and ankle extensors during walking (1.6 m/s), running (4.1 m/s) and sprinting (9.3 m/s) were quantified and then related to maximum forces of the same muscle groups obtained from a reference hopping test that permitted natural elastic limb behavior. Results: During walking, the relative effort of the ankle extensors was almost two times greater compared with the knee extensors (35±6 vs 19±5%, P<0.001). Changing walking to running decreased the difference in the relative effort between the extensors muscle groups, but still the ankle extensors operated at a 25% greater level than the knee extensors (84±12 vs 63±17%, P<0.05). At top speed sprinting, the ankle extensors reached their maximum operating level, whereas the knee extensors still worked well below their limits, showing a 25% lower relative effort compared with the ankle extensors (96±11 vs 72±19%, P<0.01). Conclusions: Regardless of mode of locomotion, humans operate at much greater relative effort at the ankle than knee extensor muscles. As a consequence, the great demand on ankle extensors may be a key biomechanical factor limiting our locomotor ability and influencing the way we locomote and adapt to accommodate compromised neuromuscular system function.

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... However, these muscle force demands may depend on the speed, length, and mode of locomotion [18]. Individuals produce greater knee and ankle extensor muscle force with each incremental increase in walk speed (from −5% to +5% of normal), and the ankle extensors operate at greater relative effort (typically near 100% of maximal capacity) than the knee extensors (between 63% and 72%, respectively) at faster locomotor speeds [19][20][21]. Considering running with body-borne load increases knee and ankle muscular activity and peak joint moments, it may also require greater knee and ankle muscle force to maintain limb stability and forward propulsion [22,23]. Substantial increases in knee and ankle muscle force, however, may increase the likelihood of lower limb musculoskeletal injury by placing "extra" stress onto the musculoskeletal system [24]. ...
... The dependent variables submitted for analysis included normalized (BW) and unnormalized (N) extensor muscle force, relative effort, and sagittal plane joint angle and angular velocity at peak muscle force for both the ankle and the knee. Each dependent variable was averaged across three successful run trials to create a participant-based mean and then submitted to a mixed model analysis of variance to test the main effects and interaction between the body-borne load (20,25,30, and 35 kg) and sex (female and male). Significant interactions were submitted to a simple effects analysis, and a Bonferroni correction was used for multiple comparisons. ...
... In agreement with our hypothesis, running with a load shifted the relative effort proximally to the knee extensors. Typically, during unloaded running, the relative effort of the knee and ankle extensors is 63% and 84% of the maximum, and the ankle extensors operate at a greater relative effort than the knee extensors, regardless of the locomotor speed [20,21]. Yet, contrary to unloaded locomotion, the current participants exhibited a relative knee extensor effort near or greater than the maximum (97% to 103%, respectively), which was between 4% and 7% above the ankle's effort (currently between 93% and 96% of the maximum). ...
Article
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Background: This study determined whether the knee and ankle muscle extensor forces increase when running with a body-borne load and whether these forces differ between the sexes. Methods: Thirty-six (twenty male and sixteen female) adults had the knee and ankle extensor force quantified when running 4.0 m/s with four body-borne loads (20, 25, 30, and 35 kg). Peak normalized (BW) and unnormalized (N) extensor muscle force, relative effort, and joint angle and angular velocity at peak muscle force for both the ankle and the knee were submitted to a mixed model ANOVA. Results: Significant load by sex interactions for knee unnormalized extensor force (p = 0.025) and relative effort (p = 0.040) were observed, as males exhibited greater knee muscle force and effort than females and increased their muscle force and effort with additional load. Males also exhibited greater ankle normalized and unnormalized extensor force (p = 0.004, p < 0.001) and knee unnormalized force than females (p = 0.005). The load increased the normalized ankle and knee muscle force (p < 0.001, p = 0.030) and relative effort (p < 0.001, p = 0.044) and the unnormalized knee muscle force (p = 0.009). Conclusion: Running with a load requires greater knee and ankle extensor force, but males exhibited greater increases in muscle force, particularly at the knee, than females.
... Previous research indicated that the plantar flexors make a significant contribution during postural stability (Onambele, Narici, & Maganaris, 2006) and greater relative effort during walking in comparison to the knee extensors (Kulmala et al., 2016). In addition, Alkner and Tesch (2004) and Akima et al. (2001) reported greater disuse-related atrophy as a result of bed rest of the plantar flexors than the knee extensors in adults. ...
... Thus, the greater mCSAs for the MG and VL of the OF children was likely due to increases in non-contractile tissue (intramuscular fat). The greater reliance on the MG during activities of daily living (Akima et al., 2001;Alkner & Tesch, 2004;Kulmala et al., 2016;Onambele et al., 2006;Trappe et al., 2009) did not serve as a mechanism that may increase mCSA/mEI or MUAP AMPS as observed following resistance training or chronic running Pope et al., 2016;. ...
... ). The MG supports activities of daily living (balance and walking) more so than the VL(Kulmala et al., 2016;Onambele et al., 2006); however, for the present study this did not translate to greater contractile tissue as the mCSA/mEI were similar for the NW and OF children.Excessive adiposity increases levels of pro-inflammatory cytokines (chronic low-grade systemic inflammation), which triggers mechanisms that contributes to skeletal muscle degradation(Fantuzzi, 2005;Hotamisligil, Murray, Choy, & Spiegelman, 1994;Sitnick, Bodine, & Rutledge, 2009).Sitnick et al. (2009) reported that the resulting chronic low-grade systemic inflammation opposes skeletal muscle growth in the presence of a load stimulus in adult OF mice. Therefore, mechanisms that lead to skeletal muscle degradation may be active in the OF children as a function of excessive adiposity, which does not allow for significant skeletal muscle growth despite the greater load stimulus. ...
Article
New findings: What is the central question of this study? Are differences in muscle size and motor unit properties between normal weight and overfat children muscle specific? What is the main finding and its importance? The main findings indicated that muscle cross-sectional area and motor unit action potential amplitudes and firing rates were similar between overfat and normal weight children for both muscles. There was no evidence that the chronic mechanical overload provided by the greater body mass resulted in significant hypertrophy of contractile tissue or motor units that would be used during lower-to-moderate intensity activities. Abstract: This study examined the possible differences in muscle cross-sectional area (mCSA), motor unit action potential amplitudes (MUAPAMPS ), and interspike intervals (ISIs) of the firing instances of the medial gastrocnemius (MG) and vastus lateralis (VL) between normal weight (NW) and overfat (OF) children aged 7-10 years. Fourteen NW (age = 8.6 ± 1.1 yrs, BMI = 15.8 ± 1.4 kg/m2 ) and 12 OF (age = 8.8 ± 0.9 yrs, BMI = 21.8 ± 2.4 kg/m2 ) children performed isometric trapezoidal muscle actions at 40% of maximal voluntary contraction (MVC) of the plantar flexors and knee extensors. Surface electromyography was recorded from the MG and VL and decomposed into the firing events of MUs. Statistical procedures were performed on the composite recruitment thresholds (RTs), ISIs, and MUAPAMPS of recorded MUs collapsed across subjects and the y-intercepts and slopes calculated from each subject's ISI and MUAPAMP vs. RT relationships. Ultrasound was used to assess mCSA, echo intensity (mEI), and subcutaneous fat (sFAT) of the MG and VL. The OF had greater mCSAs, mEI, and sFAT (P = 0.004-0.024), however, there were no differences in mCSA when accounting for mEI for the MG (P = 0.506) and VL (P = 0.326). The NW children had significantly greater composite MUAPAMPS for the VL and MG (P < 0.001), however, only significantly larger MUAPAMPS of the VL remained for the NW (P < 0.001) when subjects were matched for sFAT. There were no differences between groups for the ISI or MUAPAMP vs. RT relationships (P > 0.05). These findings suggest that the OF children did not undergo significant muscle or MU hypertrophy that would be routinely activated during activities of daily living. This article is protected by copyright. All rights reserved.
... By relating joint moments during stair walking and rising from a chair task to the maximal moments obtained from an isometric leg press test, the researchers reported a reasonable approximation of knee extensor muscle effort across the studied activities for young and old adults (42-54% vs 78-88% of maximal capacity). Recently, by using the 'matched method approach' and the all-out hopping test as a reference for maximal muscle capacity, we reported fairly realistic knee and ankle extensor muscle efforts for level walking (19% and 35%), running (63% and 84%) and sprinting (72% and 96%) in young adults 17 . When comparing the results of young adults between our work and Hortobágyi et al. (2003), it can be noted that our knee extensor effort for level walking (19%) is 2.2 and 2.8 times lower, respectively, to knee extensor effort during stair descent (42%) and ascent (54%) in the study of Hortobágyi et al. (2003), which seems reasonable, as the knee joint moments are approximately 1.5-2.5 times lower during level walking versus stair walking 18,19 . ...
... Master athletes were recruited to serve as older group to ensure that all participants were able to successfully perform the two-leg hopping task. Based on our previous work in young men 17 , we hypothesised that relative muscle effort for all three modes of locomotion would be higher at the ankle versus the knee extensors in both age groups in the present study. In comparison to young men, we predicted that older men would demonstrate similar maximum force declines in the knee and ankle extensors during the hopping reference test when compared with young men; however, due to the age-related reduction of ankle kinetics in locomotion 3,4,6 , we expected that locomotor-related muscle efforts would show a less prominent increase at the ankle versus the knee extensors in older men compared with the young men. ...
... To determine the maximum forces each participant could develop from their knee and ankle extensors during natural dynamic movement, repetitive two-leg hopping as high as possible was performed 17 . The hopping height of the older men was 13 cm lower than the younger men (20.2 cm and 33.3, p = 0.001, ES = 2.3). ...
Article
Full-text available
Age-related reduction in muscle force generation capacity is similarly evident across different lower limb muscle groups, yet decline in locomotor performance with age has been shown to depend primarily on reduced ankle extensor muscle function. To better understand why ageing has the largest detrimental effect on ankle joint function during locomotion, we examined maximal ankle and knee extensor force development during a two-leg hopping test in older and young men, and used these forces as a reference to calculate relative operating efforts for the knee and ankle extensors as participants walked, ran and sprinted. We found that, across locomotion modes in both age groups, ankle extensors operated at a greater relative effort compared to knee extensors; however, slightly less pronounced differences between ankle and knee extensor muscle efforts were present among older men, mainly due to a reduction in the ankle extensor force generation during locomotion modes. We consider these findings as evidence that reduced ankle push-off function in older age is driven by a tendency to keep ankle extensor effort during locomotion lower than it would otherwise be, which, in turn, may be an important self-optimisation strategy to prevent locomotor-induced fatigue of ankle extensor muscles.
... Participants were asked to repeatedly hop over two force plates as high as possible at least five times and repeat the hopping task after a 30 s resting period. We selected this plyometric movement as a reference test, because it has been shown to enable humans to produce the greatest extensor muscle moments from the ankle and knee joints [11,12]. ...
... In order to estimate the relative muscle effort levels for the unaffected and affected limbs during gait, we related peak moments generated during gait to maximum moments obtained from the hopping task [12,14]. This relative effort value indicated how close ankle and knee extensors operated to their maximal moment generation capacities during walking. ...
... Specifically, in this gait adaptation, the kinetic contribution from the ankle joint during stance phase is progressively reduced and replaced by a greater contribution from more proximal knee and/or hip joint musculature [17][18][19][20]. Previous studies have attributed this distal-to-proximal shift adaptation mechanism to the fact that both walking and running require greater relative efforts from the ankle extensors compared to more proximal lower limb muscle groups [12,14,21,22], thereby indicating a lower force reserve at the ankle extensors to buffer any loss of muscle capacity that may occur due to ageing, fatigue or disease. It thus seems likely that redistribution in muscular contributions, either between or within limbs, are two aspects of the same effort equalization principle that may help to optimize locomotor performance. ...
Article
Full-text available
Healthy people can walk nearly effortlessly thanks to their instinctively adaptive gait patterns that tend to minimize metabolic energy consumption. However, the economy of gait is severely impaired in many neurological disorders such as stroke or cerebral palsy (CP). Moreover, self-selected asymmetry of impaired gait does not seem to unequivocally coincide with the minimal energy cost, suggesting the presence of other adaptive origins. Here, we used hemiparetic CP gait as a model to test the hypothesis that pathological asymmetric gait patterns are chosen to equalize the relative muscle efforts between the affected and unaffected limbs. We determined the relative muscle efforts for the ankle and knee extensors by relating extensor joint moments during gait to maximum moments obtained from all-out hopping reference test. During asymmetric CP gait, the unaffected limb generated greater ankle (1.36±0.15 vs 1.17±0.16 Nm/kg, p = 0.002) and knee (0.74±0.33 vs 0.44±0.19 Nm/kg, p = 0.007) extensor moments compared with the affected limb. Similarly, the maximum moment generation capacity was greater in the unaffected limb versus the affected limb (ankle extensors: 1.81±0.39 Nm/kg vs 1.51±0.34 Nm/kg, p = 0.033; knee extensors: 1.83±0.37 Nm/kg vs 1.34±0.38 Nm/kg, p = 0.021) in our force reference test. As a consequence, no differences were found in the relative efforts between unaffected and affected limb ankle extensors (77±12% vs 80±16%, p = 0.69) and knee extensors (41±17% vs 38±23%, p = 0.54). In conclusion, asymmetric CP gait resulted in similar relative muscle efforts between affected and unaffected limbs. The tendency for effort equalization may thus be an important driver of self-selected gait asymmetry patterns, and consequently advantageous for preventing fatigue of the weaker affected side musculature.
... However, it may not reflect the demands of those sports and daily life activities that rely on submaximal muscle contractions, such as endurance running. Indeed, Kulmala et al. (2016) showed that when running at 4.1 m·s −1 , the peak force exerted by knee extensors reached the 63 ± 17% of their maximal force (calculated during hopping task). Thus, in endurance running knee extensors do not exert the maximal force they are capable of, rather they quickly produce a certain amount of force that is needed at each step for the propulsion of the body at a given speed (Kyrolainen et al., 2005;Kluitenberg et al., 2012;Bigouette et al., 2016). ...
... However, up to that level, the RFD values recorded in fatigued state were similar to those recorded in fresh state. Interestingly, a previous study (Kulmala et al., 2016) found that the peak force exerted by the knee extensors when running at 4.1 m·s −1 reached the ≈63% of maximal force, which is below the limit where the RFD was unaltered by fatigue in the present study. Together, these findings can explain why a recent meta-analysis showed that muscle fatigue did not significantly change the ground reaction force active peak and loading rate in running (Zadpoor and Nikooyan, 2012). ...
Article
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The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks that require participants to reach as quickly as possible maximal or near-maximal force. However, endurance sports require athletes to quickly produce force of submaximal, rather than maximal, amplitudes. Thus, this study investigated the effect of muscle fatigue induced by long-distance running on the capacity to quickly produce submaximal levels of force. Twenty-one male amateur runners were evaluated before and shortly after a half-marathon race. Knee extensors force was recorded under maximal voluntary and electrically evoked contractions. Moreover, a series of ballistic contractions at different submaximal amplitudes (from 20 to 100% of maximal voluntary force) was obtained, by asking the participants to reach submaximal forces as fast as possible. The RFD was calculated for each contraction. After the race, maximal voluntary activation, resting doublet twitch, maximal force, and RFD during maximal contraction decreased (−12, −12, −21, and −19%, respectively, all P-values < 0.0001). Nevertheless, the RFD values measured during ballistic contractions up to 60% of maximal force were unaffected (all P-values > 0.4). Long-distance running impaired the capacity to quickly produce force in ballistic contractions of maximal, but not of submaximal, amplitudes. Overall, these findings suggest that central and peripheral fatigue do not affect the quickness to which muscle contracts across a wide range of submaximal forces. This is a relevant finding for running and other daily life activities that rely on the production of rapid submaximal contractions rather than maximal force levels.
... Superior running performance is achieved by large moments of the hip, knee, and ankle joints. Among these lower extremity joints, the role of the ankle plantar flexor moment as an energy source during running is relatively larger compared to other joint moments [22,24], and the plantar flexor muscle strongly contributes to body support and propulsion during the contact phase [11,24]. Thus, the prop-erties of the plantar flexors may help achieve superior running performance, potentially by enhancing running economy, in endurance runners. ...
... Because of the increased running velocity, a reduced contact time is required [5,27]. The reduced contact time is associated with enhancement of vertical ground reaction force during the stance phase [27], which is partially due to increased plantar flexor force [22,24]. A stiffer plantar flexor MTC may be useful to generate a larger force with a smaller angular change at the ankle joint during stance phase. ...
Article
The present study aimed to determine the relationship between passive stiffness of the plantar flexors and running performance in endurance runners. Forty-eight well-trained male endurance runners and 24 untrained male control subjects participated in this study. Plantar flexor stiffness during passive dorsiflexion was calculated from the slope of the linear portion of the torque-angle curve. Of the endurance runners included in the present study, running economy in 28 endurance runners was evaluated by measuring energy cost during three 4-min trials (14, 16, and 18 km/h) of submaximal treadmill running. Passive stiffness of the plantar flexors was significantly higher in endurance runners than in untrained subjects. Moreover, passive plantar flexor stiffness in endurance runners was significantly correlated with a personal best 5000-m race time. Furthermore, passive plantar flexor stiffness in endurance runners was significantly correlated with energy cost during submaximal running at 16 km/h and 18 km/h, and a trend towards such significance was observed at 14 km/h. The present findings suggest that stiffer plantar flexors may help achieve better running performance, with greater running economy, in endurance runners. Therefore, in the clinical setting, passive stiffness of the plantar flexors may be a potential parameter for assessing running performance.
... Large lower limb joint moments are required to achieve superior running performance [15]. Of those, larger ankle plantar flexor moments play an important role in achieving higher running performance compared to other lower limb joint moments [9,15]. The metatarsophalangeal (MTP) flexor moment in the foot contributes to enhancing the plantar flexor moment [1,10], potentially by storing and then returning the elastic energy during human locomotion, including running [2,8,12,21,26]. ...
... Because the plantar flexor moments play an important role during running [9,15], longer forefoot bones may potentially contribute to higher running performance by enhancing the plantar flexor moments [1,10]. In addition, the availability of the elastic energy during running may be an important factor to achieve superior running performance, especially good running economy, in endurance runners [18]. ...
Article
Recently, we reported that the forefoot bones were longer in sprinters than in non-sprinters, and that longer forefoot bones correlated with higher sprint performance in sprinters. To further understand the superiority of long forefoot bones in athletic performance, we examined whether forefoot bone length was associated with running performance in endurance runners. The length of the forefoot bones of the big and second toes were measured using magnetic resonance imaging in 45 male well-trained endurance runners and 45 male untrained subjects. After normalization with the foot length, it was found that the forefoot bones of the big and second toes were significantly longer in endurance runners than in untrained subjects (P<0.05 for both). Furthermore, longer forefoot bones of the big toe, but not of the second toe, correlated significantly with better personal best 5000-m race time in endurance runners (r=−0.322, P=0.031). The present findings demonstrated that forefoot bones were longer in endurance runners than in untrained subjects. These findings were similar to our findings for sprinters. In addition, we found that longer forefoot bones may be advantageous for achieving higher running performance in endurance runners.
... Loss of muscle mass in humans after the age of 50 years is largely attributable to declines in lower body muscle mass [1], which has implications for mobility in older age. Specifically, the leg extensor muscle-tendon groups critical for gait [2][3][4] show reduced muscle strength and altered tendon mechanical properties in older, compared to younger adults [5][6][7][8]. Lower limb muscle strength [9][10][11][12], power [11,13,14] and quality [15,16] have been associated with daily life falls incidence in older adults, although findings are not unequivocal [12,13,[17][18][19]. ...
... We feel that the current measure gives a more general overall indicator that is more robust to individual differences in response behaviour. It should also be kept in mind that our muscle biopsies came from the vastus lateralis muscle which is not necessarily the most critical muscle for gait [2][3][4] (although it likely plays an important role in leg extension and energy absorption during the initial recovery steps) nor entirely representative of the fibre type properties from other lower limb muscles [90][91][92]. Finally, one potential limitation is the exploratory nature of some of the correlations and the lack of a priori correction for multiple comparisons. ...
Preprint
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Falls among older adults are often attributed to declining muscle strength with ageing. Associations between muscle strength and balance control have been reported, but the evidence for, and key mechanisms of resistance exercise in fall prevention are unclear. No studies have directly examined the relationship between muscle fibre characteristics and reactive balance control. Here, we address whether or not Type II muscle fibre characteristics associate with reactive balance during walking in young and older adults with varying muscle fibre type composition. We analyse muscle biopsy-derived fibre characteristics and stability during a treadmill-based walking perturbation (trip-like) task of healthy young adults, healthy, normally active older adults, trained older adults and physically impaired older adults. We find no significant associations between Type II muscle fibre properties and reactive balance during walking, indicating that practitioners and researchers should consider more than just the muscle tissue properties when assessing and intervening on fall risk.
... This was based on the notion that during the prolonged run the calculated ankle joint moments were higher than calculated peak knee and hip joint moments relative to previously-reported maximum joint moments assessed during isolated strength tests (Anderson et al., 2007). This confirmed previous reports of higher relative efforts of the ankle extensors compared to knee extensors during running (Kulmala et al., 2016). ...
Thesis
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The latest records set during long-distance running competitions have been attributed to recent footwear midsole innovations. One of these midsole innovations that has been claimed to have large effects on biomechanical, physiological, and performance variables is the use of a carbon fibre plate to increase the longitudinal bending stiffness of a shoe. Several mechanisms were proposed to be associated with performance improvements when running in footwear with carbon fibre plates. One of these mechanisms, the principle of optimising muscle function is currently not well understood. Therefore, this thesis aimed to investigate the effects of midsole bending stiffness of athletic footwear on muscle and muscle-tendon unit function in running. The first part of this thesis showed that running in stiff footwear resulted in a redistribution of positive work from proximal to distal lower limb joints. Specifically, it was found that a fatigue-induced redistribution of joint work from distal to proximal joints can be delayed when running in stiff footwear. The second part of this thesis dealt with the shortening velocities of muscle-tendon units. Estimated shank muscle-tendon unit shortening velocities were reduced when running in stiffer shoes. Experimental results using ultrasound imaging of the gastrocnemius medialis muscle revealed that the muscle shortened to a lesser extent and with lower average velocities in stiff running footwear. These findings could have implications for long-distance running performance. Positive work generation at more distal joints (i.e., ankle) may result in lower active muscle volume, which has been shown to be the main determinant of changes in the energetic cost of running. Slower shortening velocities of the gastrocnemius medialis could allow the muscle to operate on a more favourable position on its force-velocity relationship. This could allow for more economical force generation for a longer period during long-distance running. Altered muscle function could be a source of improved performance when running in stiff shoes.
... Participants then performed a double-limb vertical hopping task to a metronome sound set at a frequency of 2.0 Hz, which represents a common movement frequency for this movement task. 19 Vertical hopping was chosen because it is an ankle dominant movement task, and more dynamic than walking such that it would elicit greater differences between MFM. 20 After brief familiarization with the hopping task and frequency, participants hopped continuously for approximately 10 seconds. The three-dimensional positions of the markers were recorded with 14 motion capture cameras (Vicon 612, Vicon, Los Angeles, CA, USA) at 100 Hz. ...
Article
Multi-segment foot models (MFM) are becoming a common tool in musculoskeletal research of the foot-ankle complex. The purpose of this study was to compare ankle joint kinematics as well as ligament and muscle strains that result from MFM with different number of segments during vertical hopping. Ten participants were recruited and performed double-limb vertical hops. Marker positions and ground reaction forces were collected. Two-segment (2MFM), three-segment (3MFM), and five-segment (5MFM) MFM were used to calculate ankle kinematics and the strains of the anterior talofibular and calcaneofibular ligaments and of the soleus and gastrocnemius muscles. Ranges of motion and peak strains were analyzed with Kruskal-Wallis and post-hoc tests, whereas the time-series of the ankle kinematics and ligament and muscle strains were analyzed with statistical parametric mapping. There were significant main effects for MFM in talocrural joint range of motion, peak strains of ligaments and muscles. In addition, there were significant main effects for MFM in time-series data of the talocrural joint angle as well as for ligament and muscle strains. In all cases, the post-hoc analyses showed that the 2MFM consistently overestimated range of motion and tissue strains compared to the 3MFM and 5MFM, while 3MFM and 5MFM did not differ from each other in the most variables. This study showed that the number of segments in MFM significantly affects biomechanical estimates of joint kinematics and tissue strains during hopping. Clinical Significance: MFM that combine all foot structures beyond the talus into one segment likely overestimate ankle joint biomechanics. This article is protected by copyright. All rights reserved.
... Likewise, Thelen et al. (1996) also found age-re- lated differences in normalized dorsiflexor isokinetic PT (0.52-2.09 rad·s − 1 ). The discrepancies between our findings and these previous studies may be due to muscle specific differences ( Kulmala et al., 2016;Thelen et al., 1996) and/or the physical activity status of the participants (Kent- Braun et al., 2000). For instance, participants in the Lanza et al. (2003) study are described as "minimally active" and "sedentary to recreationally active", whereas participants in the Jenkins et al. (2015) study ranged from 1 to 15 h in aerobic exercise, resistance exercise, and recreational sports. ...
... Using an inverse dynamics approach to quantify muscle forces at the ankle, Kulmala et al. (2016) recently demonstrated that running at 246 m•min -1 required 84% of maximal muscle force of the ankle extensors, making these muscles likely the most susceptible to fatigue and/or muscle injury. These values are remarkably similar to our mean value for muscle activation (85%). ...
Article
We have recently demonstrated that the triceps surae muscles energy cost (ECTS) represents a substantial portion of the total metabolic cost of running (Erun). Therefore, it seems relevant to evaluate the factors which dictate ECTS, namely the amount and velocity of shortening, since it is likely these factors will dictate Erun. Erun and triceps surae morphological and AT mechanical properties were obtained in 46 trained and elite male and female distance runners using ultrasonography and dynamometry. ECTS (J·stride-1) at the speed of lactate threshold (sLT) was estimated from AT force and crossbridge mechanics and energetics. To estimate the relative impact of these factors on ECTS, mean values for running speed, body mass, resting fascicle length (Lf), Achilles tendon stiffness and moment arm and maximum isometric plantarflexion torque were obtained. ECTS was calculated across a range (mean ± 1 sd) of values for each independent factor. Average sLT was 233 m·min-1. At this speed, ECTS was 255 J·stride-1. Estimated fascicle shortening velocity was 0.08 Vmax and the level of muscle activation was 84.7% of maximum isometric torque. Compared to the ECTS calculated from the lowest range of values obtained for each independent factor, higher AT stiffness was associated with a 39% reduction in ECTS, 81% reduction in fascicle shortening velocity and a 31% reduction in muscle activation. Longer AT moment arms and elevated body masses were associated with an increase in ECTS of 18% and 23%, respectively. These results demonstrate that a low ECTS is achieved primarily from a high AT stiffness and low body mass, which is exemplified in elite distance runners.
... It is estimated that around 64% of the MU pool would be acti- Slope (pps/%MVC) Slope (µV/%MVC) y = -0.009455x + 1.032e-005 R 2 = 0.5222 Fig. 7 The plotted correlation between the slopes from the motor unit action potential amplitudes (MUAP AMP ) vs. recruitment threshold (RT) (y-axis) and the mean firing rate (MFR) vs. RT (x-axis) relationships are routinely activated during moderate-intensity running (Kulmala et al. 2016). Although the MUs activated during moderate-intensity running and the 40% MVC would be termed "lower threshold", the muscle fibers that comprise these MUs would express both type I or type II characteristics (Enoka and Duchateau 2008;Enoka and Fuglevand 2001). ...
Article
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This study examined motor unit (MU) amplitudes (APAMPS) and firing rates during moderate-intensity contractions and muscle cross-sectional area (mCSA) and echo intensity (mEI) of the vastus lateralis (VL) in chronically endurance-trained and sedentary females. Eight endurance-trained (ET) and nine sedentary controls (SED) volunteered for this study. Surface electromyographic (EMG) signals from a five-pin electrode array were recorded from the VL during isometric trapezoid muscle actions at 40% of maximal voluntary contraction (MVC). Decomposition methods were applied to the EMG signals to extract the firing events and amplitudes of single MUs. The mean firing rate (MFR) during steady force and MUAPAMP for each MU was regressed against recruitment threshold (RT, expressed as %MVC). The y-intercepts and slopes from the MFR and MUAPAMP vs. RT relationships were calculated. EMG amplitude during steady force was normalized (N-EMGRMS) to peak EMG amplitude recorded during the MVC. Ultrasonography was used to measure mCSA and mEI. Significant differences existed between the ET and SED for the slopes (P = 0.005, P = 0.001) from the MFR and MUAPAMP vs. RT relationships with no differences for the y-intercepts (P > 0.05). N-EMGRMS was significantly (P = 0.033) lower for the ET than SED. There were no differences between groups for mCSA; however, the SED possessed significantly (P = 0.001) greater mEI. Subsequently, the ET likely possessed hypertrophied and stronger MUs that allowed for lower necessary muscle activation to maintain the same relative task as the SED. The larger MUs for the ET is supported via the MFR vs. RT relationships and ultrasound data.
... Collectively, these results support the idea that WBVT could be an effective training method to increase lower limb isometric strength in young adults, but we extend previous findings to show that significant increases can be achieved across a broad range of joint angles in the plantar flexor muscles. These results are of substantial practical importance in patient populations given that the plantar flexor muscles are an important power producer during human locomotion 17 and that the loss of plantar flexor function appears to primarily influence gait performance in clinical and elderly populations. 18 Additionally, these changes were observed through the full range of motion (ROM), so the strength increase may be expected to impact performance in a variety of daily tasks, irrespective of the joint position or ROM required. ...
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The purposes of this study were to determine the impact of 6 weeks of whole-body vibration training (WBVT) on maximum voluntary plantar flexor strength, muscle activity via surface electromyography (EMG), and muscle architecture measured at rest and during maximal contraction at different ankle joint angles in young healthy adults. Using a single-blind study design, 28 healthy men and women were randomly assigned to control (CG; n=14, 7 women) or whole-body vibration training (WBVG; n=14, 7 women) groups. Vibration training (20-25 min; standing with knees flexed) was performed 3∙wk-1 for 6 weeks (18 sessions). Maximum isometric plantar flexor torque, muscle activity (medial and lateral gastrocnemius EMG) and medial gastrocnemius fascicle angle and length at rest and maximum contraction were tested at four ankle joint angles (ranging 45° - -15°; 0°=anatomical) before and after training. Significant increases (24.7-37.5%) were observed in peak torque (N∙m∙kg-1 ) at -15, 0, 15 and 30° joint angles from pre- to post-intervention in WBVG, which were different to CG (no change) and greater at longer muscle lengths. No between-group differences were observed in changes in EMG amplitudes measured during contraction or muscle architecture parameters at rest or during contraction. Six weeks of WBVT in young, healthy adults increased isometric plantarflexion strength at multiple joint angles, without detectible changes in EMG, muscle architecture or body composition. Therefore, WBVT can significantly improve maximum plantar flexor strength at multiple joint angles (muscle lengths) in young healthy men, although the mechanisms underpinning the changes are currently unclear.
... Our introduction highlighted the capacity of the soleus for force generation and our findings of twice bodyweight force output (in knee flexion) equate to soleus intramuscular force of approximately six to eight times body weight when typical lever arms are calculated for the ankle joint. It would appear likely that rehabilitating force capacity to levels of around twice bodyweight would allow the plantar flexors to function within normal physiologic levels during locomotion and that this may account for improvements in the clinical manifestation of AT (Debenham et al., 2016;Kulmala et al., 2016;O'Neill et al., 2015). It is important that rehabilitation also target the bilateral weakness identified as this may explain the high rates of the asymptomatic limb becoming symptomatic in the future. ...
Article
Objectives: Determine how the strength and endurance of the plantar flexors are affected by Achilles tendinopathy and whether one muscle is more affected than another. Design: Case control study. Setting: University Laboratory. Participants: 39 Runners with mid-portion Achilles tendinopathy and 38 healthy runners participated in this study. Main outcome measures: Isokinetic dynamometry was completed bilaterally in two knee positions on all subjects to assess the torque and endurance capacity of the plantar flexors. Results: Subjects with Achilles tendinopathy were statistically weaker (by 26.1Nm Concentric 90°/sec, 14,8Nm Concentric 225°/sec and 55.5Nm Eccentric 90°/sec for knee extended testing and 17.3Nm, 10.1Nm and 52.3Nm for the flexed knee respectively) than healthy controls at all isokinetic test speeds and contraction modes irrespective of knee position (p value = <0.001). The endurance capacity of the plantar flexors was significantly reduced (Total work done 613.5Nm less) in subjects with Achilles tendinopathy when compared to the healthy controls (p value = <0.001). Conclusions: Achilles tendinopathy is associated with large deficits in plantar flexor torque and endurance. The deficits are bilateral in nature and appear to be explained by a greater loss of the soleus force generating capacity rather than the gastrocnemius.
... Of note, changes in the current study are lower than the reported variability (CV = 9-12%) (Troester et al. 2018); however, the possibly small changes may represent a bias toward impaired performance post-training. Although balance measures represent a static task, ankle musculature is reported as the biomechanical limiting factor to locomotor activities (particularly running and sprinting), given the greater relative effort compared to knee extensor musculature (Kulmala et al. 2016) and represents the weakest link in this kinetic chain. Given the acute post-training responses noted here, single-leg non-dominant measures of balance may present a possible measure of NMF with the added benefit of less physical effort than landing and CMJ tests. ...
Article
Purpose: This study investigated responses of single-leg balance and landing and countermovement jump (CMJ) following rugby union training and the specific components of training load associated with test decrement. Methods: Twenty-seven professional rugby union players performed CMJ, single-leg balance and landing tests on a 1000 Hz force plate at the beginning and end of training days. Training load was described by session RPE, Banister’s TRIMP, GPS total distance, high-speed running distance (>5.5 m s⁻¹), relative speed and body load. Results: CMJ eccentric rate of force development (EccRFD) demonstrated moderate impairment post-training (ES ± 90%CL = −0.79 ± 0.29, MBI = almost certainly). CMJ height (−0.21 ± 0.16, possible), concentric impulse (ConIMP) (−0.35 ± 0.17, likely) and single-leg balance sway velocity on the non-dominant leg (0.30 ± 0.26, possible) were also impaired. Regression analyses identified the strongest relationship between sRPE and impaired ConIMP (r = −0.68 ± 21, β = −0.68) whilst other load measures explained 27–50% of the variance in balance and CMJ changes. Conclusions: CMJ variables representing altered movement strategy (EccRFD and IMP) may be useful for assessing acute neuromuscular fatigue in rugby union, though single-leg balance sway velocity may be an alternative when maximal tests are impractical.
... The effective performance of running depends on the joint's adaptability, which may reflect the runners' neuromusculoskeletal capacities. This result reinforces the importance of considering each joint's specificities according to the task during training sessions (Kulmala et al., 2016). For example, implementing variability-based interventions (e.g., differential learning (Schöllhorn et al., 2006)) that further consider the higher adaptability demand applied on the ankle joint during running. ...
Article
This study aimed to investigate the regularity of the lower limb joint kinematics in runners with and without a history of running-related injuries. The second aim was to verify if the movement pattern regularities are different among the lower limb joints. Eighteen asymptomatic recreational runners with and without a history of running-related injury participated in this study. Lower limb kinematics in the sagittal plane were recorded during running on a treadmill at a self-selected speed. The regularities of the time series of hip, knee, and ankle were analysed using sample entropy (SampEn). A mixed analysis of variance was used to investigate differences between groups and among joints. Runners with a history of injury had lower SampEn values than runners without a history of injury. Ankle kinematics SampEn was higher than that of the knee and hip. Knee kinematics had higher values of SampEn than that of the hip. Runners with a history of running-related injury had greater joint kinematic’s regularity. This result suggests that, even in asymptomatic runners, previous injuries could influence the movement pattern regularity. Also, the regularity was different among joints. The ankle demonstrated the lowest regularity, reinforcing the different functions that lower limb joints perform during running.
... Another limitation is that there was no electromyography (EMG) data to validate the muscle activation patterns. However, the simulated muscle forces and activation timings are consistent with previously published data for healthy individuals during walking (Alexander and Schwameder, 2016;Besier et al., 2009;Gomes et al., 2017;Kulmala et al., 2020Kulmala et al., , 2016Lin et al., 2012). Future studies should be conducted to generate a PAD model with appropriate muscle characteristics, so the muscle mechanics of patients with PAD can be truly replicated. ...
Article
Patients with peripheral artery disease (PAD) have significantly reduced lower extremity muscle strength compared with healthy individuals as measured during isolated, single plane joint motion by isometric and isokinetic strength dynamometers. Alterations to the force contribution of muscles during walking caused by PAD are not well understood. Therefore, this study used simulations with PAD biomechanics data to understand lower extremity muscle functions in patients with PAD during walking and to compare that with healthy older individuals. A total of 12 patients with PAD and 10 age-matched healthy older controls walked across a 10-meter pathway with reflective markers on their lower limbs. Marker coordinates and ground reaction forces were recorded and exported to OpenSim software to perform gait simulations. Walking velocity, joint angles, muscle force, muscle power, and metabolic rate were calculated and compared between patients with PAD and healthy older controls. Our results suggest that patients with PAD walked slower with less hip extension during propulsion. Significant force and power reductions were observed in knee extensors during weight acceptance and in plantar flexors and hip flexors during propulsion in patients with PAD. The estimated metabolic rate of walking during stance was not different between patients with PAD and controls. This study is the first to analyze lower limb muscular responses during walking in patients with PAD using the OpenSim simulation software. The simulation results of this study identified important information about alterations to muscle force and power during walking in those with PAD.
... While this motion is frequently performed during training or competition by athletes in jump-related sports such as basketball and volleyball, other motions are also common (e.g., side-stepping or cutting). Hopping, however, was chosen as a movement task because it requires almost maximal activation of the plantarflexor muscles (Kulmala et al. 2016). Regardless, to better understand the importance of talus alignment with respect to risk of injury, etc., it may be necessary to investigate other movements as well. ...
Article
The purpose of the present study was to identify the effects of anterior translation and medial rotation of the talus on ankle joint contact forces (AJF) during double-limb vertical hopping. A computational musculoskeletal model was used to calculate AJF under 225 different combinations of 0-10 mm (in 10/15 mm increments) anterior translation and 0-5° (in 5/15° increments) medial rotation for ten subjects. The results show anteroposterior AJF was moderately affected by anterior translation, while mediolateral AJF was strongly affected by medial rotation. Future research should investigate if interventions that manipulate misaligned talus position in-vivo can also reduce AJF.
... Degeneration processes such as aging can modify this alteration: for example, an age-associated strength decrease may lead to a distal-to-proximal (ankle to hip) shift of joint work 39-41 that can affect locomotor ability. 42,43 Naturally, the neuromuscular system's aging implies a continuous functional decline caused by time-dependent, accumulated cellular damage 44,45 that results in age-related loss of muscle mass and function. This loss is strongly related to physical disability, 46,47 functional impairments, 48 and even mortality, 49 whereby the loss of strength contributes proportionally more to predicting disability than does muscle mass. ...
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Background: After allogeneic hematopoietic cell transplantation (alloHCT), patients often report functional impairments like reduced gait speed and muscle weakness. These impairments can increase the risk of adverse health events similar to elderly populations. However, they have not been quantified in patients after alloHCT (PATs). Methods: We compared fear of falling (Falls Efficacy Scale–International) and temporal gait parameters recorded on a 10-m walkway at preferred and maximum gait speed and under dual-task walking of 16 PATs (aged 31-73 years) with 15 age-matched control participants (CONs) and 17 seniors (SENs, aged >73 years). Results: Groups’ gait parameters especially differed during the maximum speed condition: PATs walked slower and required more steps/10 m than CONs. PATs exhibited greater stride, stance, and swing times than CONs. PATs’ swing time was even longer than SENs’. The PATs’ ability to accelerate their gait speed from preferred to fast was smaller compared with CONs’. PATs reported a greater fear of falling than CONs and SENs. Conclusion: Gait analysis of alloHCT patients has revealed impairments of functional performance. Patients presented a diminished ability to accelerate gait and extending steps possibly related to a notable strength deficit that impairs power-generation abilities from lower extremities. Furthermore, patients reported a greater fear of falling than control participants and even seniors. Slowing locomotion could be a risk-preventive safety strategy. Since functional disadvantages may put alloHCT patients at a higher risk of frailty, reinforcing appropriate physical exercises already during and after alloHCT could prevent adverse health events and reduce the risk of premature functional aging.
... 11,12 Furthermore, although the relative contribution of the plantar flexor torque during sprinting may be higher than that of the knee joint torque, this contribution may be lower than that of the hip joint torque. 1,11,12,30 Therefore, an increase in the plantar flexor torque depending on the AT morphological and mechanical variables may have a little effect on achieving superior 100-m sprint performance in sprinters. In summary, the findings of the present study may indicate the low contributions of the AT variables and plantar flexor torque during superior 100-m sprinting. ...
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This study examined the relationship between Achilles tendon (AT) length and 100-m sprint time in sprinters. The AT lengths at 3 different portions of the triceps surae muscle in 48 well-trained sprinters were measured using magnetic resonance imaging. The 3 AT lengths were calculated as the distance from the calcaneal tuberosity to the muscle-tendon junction of the soleus, gastrocnemius medialis, and gastrocnemius lateralis, respectively. The absolute 3 AT lengths did not correlate significantly with personal best 100-m sprint time (r = -.023 to .064, all Ps > .05). Furthermore, to minimize the differences in the leg length among participants, the 3 AT lengths were normalized to the shank length, and the relative 3 AT lengths did not correlate significantly with personal best 100-m sprint time (r = .023 to .102, all Ps > .05). Additionally, no significant correlations were observed between the absolute and relative (normalized to body mass) cross-sectional areas of the AT and personal best 100-m sprint time (r = .012 and .084, respectively, both Ps > .05). These findings suggest that the AT morphological variables, including the length, may not be related to superior 100-m sprint time in sprinters.
... We used relative speeds since it has been demonstrated that older adults prefer slower walking speeds, which may be an attempt to compensate for decreased plantarflexor strength (Stenroth, Sipilä, Finni, & Cronin, 2016). Thus, the use of matched speeds could lead to increased metabolic penalties in the elderly that are associated with the requirements imposed by the walking speed rather than the aging process (Kulmala et al., 2016). Nevertheless, it should be noted that both comparing COT across preferred speeds and comparing COT at fixed speeds give rise to challenges that should be considered in the interpretation of results. ...
Article
This study examined the contributions of individual muscles to changes in energetic cost of transport (COT) over seven walking speeds, and compared results between healthy young and elderly subjects. Twenty six participants (13 young aged 18-30; 13 old aged 70-80) were recruited. COT (O2/kg body mass/km) was calculated by standardizing the mean oxygen consumption recorded during steady state walking. Electromyography signals from 10 leg muscles were used to calculate the cumulative activity required to traverse a unit of distance (CMAPD) for each muscle at each speed. In the old group CMAPD was correlated with COT, presented higher and more variable values, and showed greater increases around optimal speed for all studied muscles. Soleus CMAPD was independent of speed in the young group, but this was not evident with aging. Greater energy cost of walking in older individuals seems to be attributable to increased energy cost of all lower limb muscles.
Article
The purpose of this study was to examine the effect of speed on coordination and its variability in running gait using vector coding analysis. Lower extremity kinematic data were collected for thirteen recreational runners while running at three different speeds in random order: preferred speed, 15% faster and 15% lower than preferred speed. A dynamical systems approach, using vector coding and circular statistics, were used to quantify coordination and its variability for selected hip-knee and knee-ankle joint couplings. The influence of running speed was calculated from the continuous data sets of the running cycle, allowing for the identification of time per- centages where differences existed. Results indicate that increases in running speed produced moderate alterations in the frequency of movement patterns which were not enough to alter classification of coordination. No effects of speed on coordination variability were observed. This study has demonstrated that coordination and coordination variability is generally stable in the range of±15% around of preferred speed in recreational runners.
Article
Older adults often walk with smaller ankle joint kinetics and larger hip joint kinetics compared to young adults. These age-related differences have been attributed, in part, to weaker plantarflexor muscles. While it is thought that regular physical activity helps to maintain muscle strength and mobility in older adults, physical activity levels on average decline with age. Therefore, understanding the effect of physical activity level on gait kinetics is an important objective for the management of mobility impairment in older adults. The purpose of this study was determine the effect of habitual endurance running on lower-extremity joint kinetics. 12 male older runners (67 ± 5 yrs., 1.79 ± 0.07 m, 77.3 ± 13.7 kg) and 12 male older non-runners (70 ± 3 yrs., 1.78 ± 0.06 m, 79.68 ± 10.6 kg), performed overground walking trials at 1.3 m/s while kinematic and kinetic data were collected. Participants also performed maximal voluntary contractions (MVC) at the hip, knee, and ankle joints on an isokinetic dynamometer. Older runners displayed similar ankle plantarflexor strength, similar hip extensor strength, and greater knee extensor strength compared to older non-runners, and walked with similar ankle joint kinetics (p > 0.05), and larger hip joint kinetics compared to older non-runners (p < 0.05). Thus, physical activity, in the form of running at least 20 miles/wk. and training for at least one race per year, did not mitigate the characteristic age-related differences in gait kinetics. Our findings may indicate that age-related differences in lower-extremity gait kinetics are a normal consequence of natural aging.
Article
Background High vertical loading rate is associated with a variety of running-related musculoskeletal injuries. There is evidence supporting that non-rearfoot footstrike pattern, greater cadence, and shorter stride length may reduce the vertical loading rate. These features appear to be common among preschoolers, who seem to experience lower running injury incidence, leading to a debate whether adults should accordingly modify their running form. Objective This study sought to compare the running biomechanics between preschoolers and adults. Methods Ten preschoolers (4.2 ± 1.6 years) and ten adults (35.1 ± 9.5 years) were recruited and ran overground with their usual shoes at a self-selected speed. Vertical average (VALR) and vertical instantaneous loading rate (VILR) were calculated based on the kinetic data. Footstrike pattern and spatiotemporal parameters were collected using a motion capture system. Results There was no difference in normalized VALR (p = 0.48), VILR (p = 0.48), running speed (p = 0.85), and footstrike pattern (p = 0.29) between the two groups. Preschoolers demonstrated greater cadence (p < 0.001) and shorter normalized stride length (p = 0.01). Conclusion By comparing the kinetic and kinematic parameters between children and adults, our findings do not support the notion that adults should modify their running biomechanics according to the running characteristics in preschoolers for a lower injury risk.
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Objective: To investigate if changing the midsole bending stiffness of athletic footwear can affect the onset of lower limb joint work redistribution during a prolonged run. Methods: Fifteen trained male runners (10-km time < 44 min.) performed 10-km runs at 90% of their individual speed at lactate threshold (i.e., when change in lactate exceeded 1 mmol during an incremental running test) in a control and stiff shoe condition on two occasions. Lower limb joint kinematics and kinetics were measured using a motion capture system and a force-instrumented treadmill. Data was acquired every 500 m. Results: Prolonged running resulted in a redistribution of positive joint work from distal to proximal joints in both shoe conditions. Compared to the beginning of the run, less positive work was performed at the ankle (~9%, p ≤ 0.001) and more positive work was performed at the knee joint (~17%, p ≤ 0.001) at the end of the run. The onset of joint work redistribution at the ankle and knee joint occurred at a later point during the run when running in the stiff shoe condition. Conclusion: A delayed onset of joint work redistribution in the stiff condition may result in less activated muscle volume, because ankle plantarflexor muscles have shorter muscles fascicles and smaller cross-sectional areas compared to knee extensor muscles. Less active muscle volume could be related to previously reported decreases in metabolic cost when running in stiff footwear. These results contribute to the notion that footwear with increased stiffness likely results in reductions in metabolic cost by delaying joint work redistribution from distal to proximal joints.
Article
Identifying the neuromechanical changes during high-intensity running to fatigue may highlight the biomechanical limitations to performance and indicate mitigation/training strategies. Purpose: To investigate the changes in lower limb kinematics, kinetics and muscle activation during a high-intensity run to fatigue (HIRF). Methods: 18 male and female competitive middle-distance runners performed a HIRF on an instrumented treadmill at a constant, but unsustainable middle-distance speed (~3 min) based on a preceding maximum oxygen uptake (V[Combining Dot Above]O2max) test. Three-dimensional kinematics and kinetics were collected and compared between the start, 33%, 67%, and the end of the HIRF. Additionally, activation of eight lower limb muscles of each leg were measured with surface electromyography (sEMG). Results: Time to exhaustion was 181 ± 42 s. By the end of the HIRF (i.e. vs the start): ground contact time increased (+4.0%); whilst flight time (-3.2%), peak vertical ground reaction force (-6.1%) and vertical impulse (-4.1%) decreased (All, P<0.05); and joint angles at initial contact became more (dorsi-)flexed (ankle +1.9°; knee +2.1°; hip +3.6°; All P<0.05). During stance, by the end of the HIRF: peak ankle plantar flexion moment decreased 0.4 N·m·kg-1 (-9.0%), whereas peak knee extension moment increased 0.24 N·m·kg-1 (+10.3%); similarly, positive ankle plantar flexion work decreased 0.19 J·kg-1 (-13.9%), whereas positive knee extension work increased 0.09 J·kg-1 (+33.3%; both P<0.05) with no change in positive hip extension work. Hip extensor sEMG amplitude increased during the late swing phase (+20.9-37.3%; P<0.05). Conclusion: Running at a constant middle-distance pace led primarily to fatigue of the plantar flexors with a compensatory increase in positive work done at the knee. Improving fatigue resistance of the plantar flexors might be beneficial for middle-distance running performance.
Chapter
In order to understand any complex system like the human body, one must establish basic terms describing structure. Anatomy is the study of the structure of the body. Human anatomy provides essential labels for musculoskeletal structures and qualitative descriptions of joint motions relevant to human movement. Knowledge of anatomy also provides a common professional “language” of the human body and motions for kinesiology and medical professionals. Anatomy is an important prerequisite for kinesiology professionals trying to improve movement and prevent or treat injury. Anatomy is primarily a descriptive field of study and is not, by itself, enough to explain the function of the musculoskeletal system in creation of movement. Knowledge of anatomy must be combined with biomechanics to accurately determine the musculoskeletal and external force causes or the “how” human movement is created. This chapter reviews key anatomical concepts, shows how functional anatomy traditionally classifies muscle concentric actions, and shows how biomechanics is needed to determine the actual muscle function in movement.
Thesis
Preventing mobility disability is necessary for maintaining independent function in old age and it is well documented that various types of exercise interventions can improve walking speed in old age. However, the underlying biomechanical mechanisms of how interventions improve old adults’ gait velocity are unknown. To increase the efficacy of interventions that aim to improve walking performance and other critical mobility functions in old adults, there is a need for a paradigm shift from conventional outcome assessments (i.e., walking speed) to more sophisticated biomechanical analyses that examine joint kinematics, kinetics, and neuromuscular activation before and after interventions. This thesis aims to determine the biomechanical mechanisms how exercise and, in particular lower extremity power training, improves walking speed in old age. Based on a literature review, candidate mechanisms for how strength or power training evoke adaptations in gait biomechanics that potentially underlie training-induced increases in old adults’ walking speed are discussed. Subsequently, this thesis provides a detailed description of the design and methodology of the Potsdam Gait Study (POGS); a randomized controlled trial that examines the effects of 10 weeks of lower extremity power training on a series of biomechanical and neuromuscular outcome measures during level gait. The second half of the current thesis presents and discusses the results of POGS on stride characteristics, joint kinematics, joint kinetics, and muscle activation. Overall, the current thesis is the first to comprehensively study power training-induced adaptations in gait biomechanics that potentially underlie increases in old adults’ walking speed.
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Running has high injury rates, especially among older runners. Most aging literature compares young vs old runners without accounting for the progression of biomechanics throughout the lifespan. We used age as a continuous variable to investigate the continuum of age-related gait adaptations in running along with determining the chronology and rate of these adaptations. Identify the relationships among age and selected running biomechanics throughout the range of 18 to 60 years. Experienced (n = 110), healthy runners (54% male) provided informed consent and ran at their training pace while motion and force data were captured. Kinematics, ground reaction forces (GRFs) and lower limb joint torques and powers were correlated with age using Pearson product-moment correlations and linear regression. Running velocity was inversely related to age (r = -0.27, p = 0.005) due to decreased stride length (r = -0.25, p = 0.008) but not rate. Peak vertical GRF (r = -0.23, p = 0.016) and peak horizontal propulsive GRF decreased with age (r = -0.38, p < 0.0001). Peak ankle torque (r=-0.32, p = 0.0007), and peak negative (r = 0.34, p = 0.0003) and positive (r = -0.37, p < 0.0001) ankle power decreased with age. Age-based regression equations and per year reductions in all variables significantly related to age are reported. Data support prior work showing lower GRFs, stride length and velocity in old runners. Results are novel in showing the rate of decline in running biomechanics on a per-year basis and that mechanical reductions at the ankle but not hip or knee were correlated with age confirming previous observation of biomechanical plasticity with age showing reduced ankle but not hip function in gait.
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The interaction between the muscle-fascicle and tendon components of the human soleus (SO) muscle influences the capacity of the muscle to generate force and mechanical work during walking and running. In the present study, ultrasound-based measurements of in-vivo SO muscle fascicle behavior were combined with an inverse dynamics analysis to investigate the interaction between the muscle-fascicle and tendon components over a broad range of steady-state walking and running speeds: slow-paced walking (0.7 m s(-1)) through to moderate-paced running (5.0 m s(-1)). Irrespective of a change in locomotion mode (i.e. walking vs. running) or an increase in steady-state speed, SO muscle fascicles were found to exhibit minimal shortening compared to the muscle-tendon unit (MTU) throughout stance. During walking and running, the muscle fascicles contributed only 35% and 20% of the overall MTU length change and shortening velocity, respectively. Greater levels of muscle activation resulted in increasingly shorter SO muscle fascicles as locomotion speed increased, both of which facilitated greater tendon stretch and recoil. Thus, the elastic tendon contributed the majority of the MTU length change during walking and running. When transitioning from walking to running near the preferred transition speed (2.0 m s(-1)), greater, more economical ankle torque development is likely explained by the SO muscle fascicles shortening slower and operating on a more favorable portion (i.e. closer to the plateau) of the force-length curve. Copyright © 2015, Journal of Applied Physiology.
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Muscle mass, strength, and power are known determinants of mobility in older adults but there is limited knowledge on the influence of muscle architecture or tendon properties on mobility. The purpose of this study was to examine the relationship between mobility and plantarflexor muscle-tendon properties in healthy older adults. A total of 52 subjects (age 70-81 years) were measured for 6-minute walk test (6MWT), timed "up and go"-test (TUG), isometric plantarflexion strength, Achilles tendon stiffness, triceps surae muscle architecture, lower extremity lean mass, isometric leg extension strength, and leg extension power. Partial correlations and multivariate regression models adjusted for sex, age, body mass, and height were used to examine the relationship between mobility (6MWT and TUG) and lower limb muscle-tendon properties. Multivariate regression models revealed that Achilles tendon stiffness (p = .020), plantarflexion strength (p = .022), and medial gastrocnemius fascicle length (p = .046) were independently associated with 6MWT. Plantarflexion strength (p = .037) and soleus fascicle length (p = .031) were independently associated with TUG. Plantarflexor muscle-tendon properties were associated with mobility in older adults independent of lower extremity lean mass, leg extension strength, or power. Plantarflexion strength was a stronger predictor of mobility than leg extension strength or power. The novel finding of this study was that muscle architecture and tendon properties explained interindividual differences in mobility. This study highlights the importance of the plantarflexors for mobility in older adults and provides understanding of possible mechanisms of age-related decline in mobility. © The Author 2015. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
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Ageing leads to a progressive decline in human locomotor performance. However, it is not known whether this decline results from reduced joint moment and power generation of all lower limb muscle groups or just some of them. To further our understanding of age-related locomotor decline, we compare the amounts of joint moments and powers generated by lower limb muscles during walking (self-selected), running (4 m s(-1)) and sprinting (maximal speed) among young, middle-aged and old adults. We find that age-related deficit in ankle plantarflexor moment and power generation becomes more severe as locomotion change from walking to running to sprinting. As a result, old adults generate more power at the knee and hip extensors than their younger counterparts when walking and running at the same speed. During maximal sprinting, young adults with faster top speeds demonstrate greater moments and powers from the ankle and hip joints, but interestingly, not from the knee joint when compared with the middle-aged and old adults. These findings indicate that propulsive deficit of ankle contributes most to the age-related locomotor decline. In addition, reduced muscular output from the hip rather than from knee limits the sprinting performance in older age.
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Functional knee braces used during rehabilitation from injury and surgery to the anterior cruciate ligament (ACL) have been reported to provide a strain-shielding effect on the ACL in healthy people while standing, reduce quadriceps electromyography in ACL-deficient individuals, and alter joint torque patterns in people with ACL reconstruction during walking. These results led to the hypothesis that functional knee braces protect a reconstructed ACL during dynamic activity by reducing the anterior shear load applied to the knee. This hypothesis was tested by investigating the effects of a functional knee brace on lower extremity muscle forces and the anteroposterior shear force at the knee joint during the stance phase of walking in people with ACL reconstruction. Ground reactions and sagittal plane video were recorded from 9 ACL-reconstructed individuals as they walked with and without a functional knee brace, and from 10 healthy people without the functional knee brace. Inverse dynamics were used to calculate the net joint torques in the lower extremity during the stance phase. Hamstrings, quadriceps, and gastrocnemius muscle and knee anteroposterior shear force were then predicted with a sagittal-plane mathematical model. Compared to healthy individuals, those with ACL reconstruction walked with 78% more hamstrings impulse and 19% less quadriceps impulse (both p < .05). The functional knee brace produced an additional 43% increase in hamstrings impulse and an additional 13% decrease in quadriceps impulse in the ACL group. Peak anterior knee shear force and anterior impulse were 41% lower and 16% lower in ACL vs. healthy individuals, respectively. The functional knee brace further reduced the peak knee shear force and impulse 28% and 19%, respectively, in the ACL group. It was concluded that a functional knee brace protects a reconstructed ACL during walking by altering muscle forces and reducing the anterior shear force applied to the knee joint.
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It seems reasonable that quadrupeds should change gait from a walk to a trot to a gallop in such a way as to minimize their energy consumption, as human beings are known to change from a walk to a run at a particular speed (2.4 m s -1) below which walking requires less energy than running and above which the opposite is true. Thus by changing gait, human beings keep the energy cost of locomotion to a minimum as their speed increases. One reason this relation holds is that in humans, metabolic rate increases curvilinearly with walking speed. If metabolism were a curvilinear function of speed within each of the gaits used by quadrupeds, it would support the hypothesis that they also change gait to minimize energetic cost. There is an old controversy about whether metabolic rate increases linearly or curvilinearly in running humans but all previous reports have suggested that metabolic rate increases linearly with speed in quadrupeds. Extended gaits were an important experimental tool in the study of human gait changes; thus we have trained three small horses (110-170 kg) to walk, trot and gallop on a motorized treadmill, and to extend their gaits on command. We report here that, using measurements of rates of oxygen consumption as an indicator of rates of energy consumption, we have confirmed that the natural gait at any speed indeed entails the smallest possible energy expenditure.
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Humans have engaged in endurance running for millions of years, but the modern running shoe was not invented until the 1970s. For most of human evolutionary history, runners were either barefoot or wore minimal footwear such as sandals or moccasins with smaller heels and little cushioning relative to modern running shoes. We wondered how runners coped with the impact caused by the foot colliding with the ground before the invention of the modern shoe. Here we show that habitually barefoot endurance runners often land on the fore-foot (fore-foot strike) before bringing down the heel, but they sometimes land with a flat foot (mid-foot strike) or, less often, on the heel (rear-foot strike). In contrast, habitually shod runners mostly rear-foot strike, facilitated by the elevated and cushioned heel of the modern running shoe. Kinematic and kinetic analyses show that even on hard surfaces, barefoot runners who fore-foot strike generate smaller collision forces than shod rear-foot strikers. This difference results primarily from a more plantarflexed foot at landing and more ankle compliance during impact, decreasing the effective mass of the body that collides with the ground. Fore-foot- and mid-foot-strike gaits were probably more common when humans ran barefoot or in minimal shoes, and may protect the feet and lower limbs from some of the impact-related injuries now experienced by a high percentage of runners.
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Computer models that estimate the force generation capacity of lower limb muscles have become widely used to simulate the effects of musculoskeletal surgeries and create dynamic simulations of movement. Previous lower limb models are based on severely limited data describing limb muscle architecture (i.e., muscle fiber lengths, pennation angles, and physiological cross-sectional areas). Here, we describe a new model of the lower limb based on data that quantifies the muscle architecture of 21 cadavers. The model includes geometric representations of the bones, kinematic descriptions of the joints, and Hill-type models of 44 muscle-tendon compartments. The model allows calculation of muscle-tendon lengths and moment arms over a wide range of body positions. The model also allows detailed examination of the force and moment generation capacities of muscles about the ankle, knee, and hip and is freely available at www.simtk.org .
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It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris (QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F t) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated as volume divided by fascicle length during MVC. Dividing F t by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension. Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension from Method 1 (30 ± 5 N cm−2) was similar to and correlated with that of Method 2 (29 ± 5 N cm−2; R 2 = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore, a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling accurate estimations of QF specific tension where time and resources are limited.
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The physiological cross-sectional areas (CSAp) of the vastus lateralis (VL), vastus intermedius (VI), vastus medialis (VM) and rectus femoris (RF) were obtained, in vivo, from the reconstructed muscle volumes, angles of pennation and distance between tendons of six healthy male volunteers by nuclear magnetic resonance imaging (MRI). In all subjects, the isometric maximum voluntary contraction strength (MVC) was measured at the optimum angle at which peak force occurred. The MVC developed at the ankle was 746.0 (SD 141.8) N and its tendon component (F t) given by a mechanical advantage of 0.117 (SD 0.010), was 6.367 (SD 1.113) kN. To calculate the force acting along the fibres (F f) of each muscle, F t was divided by the cosine of the angle of pennation and multiplied for (CSAp · ΣCSAp−1), where ΣCSAp was the sum of CSAp of the four muscles. The resulting F f values of VL, VI, VM and RF were: 1.452 (SD 0.531) kN, 1.997 (SD 0.187) kN, 1.914 (SD 0.827) kN, and 1.601 (SD 0.306) kN, respectively. The stress of each muscle was obtained by dividing these forces for the respective CSAp which was: 6.24 × 10−3 (SD 2.54 × 10−3) m2 for VL, 8.35 × 10−3 (SD 1.17 × 10−3) m2 for VI, 6.80 × 10−3 (SD 2.66 × 10−3) m2 for VM and 6.62 × 10−3 (SD 1.21 × 10−3) m2 for RE The mean value of stress of VL, VI, VM and RF was 250 (SD 19) kN m2; this value is in good agreement with data on animal muscle and those on human parallel-fibred muscle.
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At self-selected walking speeds, elderly compared with young adults generate decreased joint torques and powers in the lower extremity. These differences may be actual gait-limiting factors and neuromuscular adaptations with age or simply a consciously selected motor pattern to produce a slower gait. The purpose of the study was to compare joint torques and powers of young and elderly adults walking at the same speed. Twelve elderly and fourteen young adults (ages 69 and 21 yr) walked at 1.48 m/s over a force platform while being videotaped. Hip, knee, and ankle torques and powers were calculated from the reaction force and kinematic data. A support torque was calculated as the sum of the three joint torques. Extensor angular impulse during stance and positive work at each joint were derived from the torques and powers. Step length was 4% shorter and cadence was 4% higher in elderly adults (both P < 0.05) compared with young adults. Support angular impulse was nearly identical between groups, but elderly adults had 58% greater angular impulse and 279% more work at the hip, 50% less angular impulse and 39% less work at the knee, and 23% less angular impulse and 29% less work at the ankle compared with young adults (t-test, all P < 0.05). Age caused a redistribution of joint torques and powers, with the elderly using their hip extensors more and their knee extensors and ankle plantar flexors less than young adults when walking at the same speed. Along with a reduction in motor and sensory functions, the natural history of aging causes a shift in the locus of function in motor performance.
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In this study, we estimated the specific tensions of soleus (Sol) and tibialis anterior (TA) muscles in six men. Joint moments were measured during maximum voluntary contraction (MVC) and during electrical stimulation. Moment arm lengths and muscle volumes were measured using magnetic resonance imaging, and pennation angles and fascicular lengths were measured using ultrasonography. Tendon and muscle forces were modeled. Two approaches were followed to estimate specific tension. First, muscle moments during electrical stimulation and moment arm lengths, fascicular lengths, and pennation angles during MVC were used (data set A). Then, MVC moments, moment arm lengths at rest, and cadaveric fascicular lengths and pennation angles were used (data set B). The use of data set B yielded the unrealistic specific tension estimates of 104 kN/m(2) in Sol and 658 kN/m(2) in TA. The use of data set A, however, yielded values of 150 and 155 kN/m(2) in Sol and TA, respectively, which agree with in vitro results from fiber type I-predominant muscles. In fact, both Sol and TA are such muscles. Our study demonstrates the feasibility of accurate in vivo estimates of human muscle intrinsic strength.
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Muscular forces generated during locomotion depend on an animal's speed, gait, and size and underlie the energy demand to power locomotion. Changes in limb posture affect muscle forces by altering the mechanical advantage of the ground reaction force (R) and therefore the effective mechanical advantage (EMA = r/R, where r is the muscle mechanical advantage) for muscle force production. We used inverse dynamics based on force plate and kinematic recordings of humans as they walked and ran at steady speeds to examine how changes in muscle EMA affect muscle force-generating requirements at these gaits. We found a 68% decrease in knee extensor EMA when humans changed gait from a walk to a run compared with an 18% increase in hip extensor EMA and a 23% increase in ankle extensor EMA. Whereas the knee joint was extended (154-176 degrees) during much of the support phase of walking, its flexed position (134-164 degrees) during running resulted in a 5.2-fold increase in quadriceps impulse (time-integrated force during stance) needed to support body weight on the ground. This increase was associated with a 4.9-fold increase in the ground reaction force moment about the knee. In contrast, extensor impulse decreased 37% (P < 0.05) at the hip and did not change at the ankle when subjects switched from a walk to a run. We conclude that the decrease in limb mechanical advantage (mean limb extensor EMA) and increase in knee extensor impulse during running likely contribute to the higher metabolic cost of transport in running than in walking. The low mechanical advantage in running humans may also explain previous observations of a greater metabolic cost of transport for running humans compared with trotting and galloping quadrupeds of similar size.
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The mechanisms that govern the voluntary transition from walking to running as walking speed increases in human gait are not well understood. The objective of this study was to examine the hypothesis that plantar flexor muscle force production is greatly impaired at the preferred transition speed (PTS) due to intrinsic muscle properties and, thus, serves as a determinant for the walk-to-run transition. The plantar flexors have been shown to be important contributors to satisfying the mechanical energetic demands of walking and are the primary contributors to the observed ground reaction forces (GRFs) during the propulsion phase. Thus, if the plantar flexor force production begins to diminish near the PTS despite an increase in muscle activation, then a corresponding decrease in the GRFs during the propulsion phase would be expected. This expectation was supported. Both the peak anterior/posterior and vertical GRFs decreased during the propulsion phase at walking speeds near the PTS. A similar decrease was not observed during the braking phase. Further analysis using forward dynamics simulations of walking at increasing speeds and running at the PTS revealed that all lower extremity muscle forces increased with walking speed, except the ankle plantar flexors. Despite an increase in muscle activation with walking speed, the gastrocnemius muscle force decreased with increasing speed, and the soleus force decreased for walking speeds exceeding 80% PTS. These decreases in force production were attributed to the intrinsic force-length-velocity properties of muscle. In addition, the running simulation analysis revealed that the plantar flexor forces nearly doubled for similar activation levels when the gait switched to a run at the PTS due to improved contractile conditions. These results suggest the plantar flexors may serve as an important determinant for the walk-to-run transition and highlight the important role intrinsic muscle properties play in determining the specific neuromotor strategies used in human locomotion.
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In the standard inverse dynamic method, joint moments are assessed from ground reaction force data and position data, where segmental accelerations are calculated by numerical differentiation of position data after low-pass filtering. This method falls short in analyzing the impact phase, e.g. landing after a jump, by underestimating the contribution of the segmental accelerations to the joint moment assessment. This study tried to improve the inverse dynamics method for the assessment of knee moment by evaluating different cutoff frequencies in low-pass filtering of position data on the calculation of knee moment. Next to this, the effect of an inclusion of direct measurement of segmental acceleration using accelerometers to the inverse dynamics was evaluated. Evidence was obtained that during impact, the contribution of the ground reaction force to the sagittal knee moment was neutralized by the moments generated by very high segmental accelerations. Because the accelerometer-based method did not result in the expected improvement of the knee moment assessment during activities with high impacts, it is proposed to filter the ground reaction force with the same cutoff frequency as the calculated accelerations. When this precaution is not taken, the impact peaks in the moments can be considered as artifacts. On the basis of these findings, we recommend in the search to biomechanical explanations of chronic overuse injuries, like jumper's knee, not to consider the relation with impact peak force and impact peak moment.
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Ultrasound imaging has recently been used to distinguish the length changes of muscle fascicles from those of the whole muscle tendon complex during real life movements. The complicated three-dimensional architecture of pennate muscles can however cause heterogeneity in the length changes along the length of a muscle. Here we use ultrasonography to examine muscle fascicle length and pennation angle changes at proximal, distal and midbelly sites of the human gastrocnemius medialis (GM) muscle during walking (4.5 km/h) and running (7.5 km/h) on a treadmill. The results of this study have shown that muscle fascicles perform the same actions along the length of the human GM muscle during locomotion. However the distal fascicles tend to shorten more and act at greater pennation angles than the more proximal fascicles. Muscle fascicles acted relatively isometrically during the stance phase during walking, however during running the fascicles shortened throughout the stance phase, which corresponded to an increase in the strain of the series elastic elements (SEEs) (consisting of the Achilles tendon and aponeurosis). Measurement of the fascicle length changes at the midbelly level provided a good approximation of the average fascicle length changes across the length of the muscle. The compliance of the SEE allows the muscle fascicles to shorten at a much slower speed, more concomitant with their optimal speed for maximal power output and efficiency, with high velocity shortening during take off in both walking and running achieved by recoil of the SEE.
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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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The load moment of force about the knee joint during machine milking and when lifting a 12.8 kg box was quantified using a computerized static sagittal plane body model. Surface electromyography of quadriceps and hamstrings muscles was normalized and expressed as a percentage of an isometric maximum voluntary test contraction. Working with straight knees and the trunk flexed forwards induced extending knee load moments of maximum 55 Nm. Lifting the box with flexed knees gave flexing moments of 50 Nm at the beginning of the lift, irrespective of whether the burden was between or in front of the feet. During machine milking, a level difference between operator and cow of 0.70 m − 1.0 m significantly lowered the knee extending moments.To quantify the force magnitudes acting in the tibio-femoral and patello-femoral joints, a local biomechanical model of the knee was developed using a combination of cadaver knee dissections and lateral knee radiographs of healthy subjects. The moment arm of the knee extensor w...
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Purpose: This study aimed to quantify differences in patellofemoral joint stress that may occur when healthy runners alter their foot strike pattern from their habitual rearfoot strike to a forefoot strike to gain insight on the potential etiology and treatment methods of patellofemoral pain. Methods: Sixteen healthy female runners completed 20 running trials in a controlled laboratory setting under rearfoot strike and forefoot strike conditions. Kinetic and kinematic data were used to drive a static optimization technique to estimate individual muscle forces to input into a model of the patellofemoral joint to estimate joint stress during running. Results: Peak patellofemoral joint stress and the stress-time integral over stance phase decreased by 27% and 12%, respectively, in the forefoot strike condition (P < 0.001). Peak vertical ground reaction force increased slightly in the forefoot strike condition (P < 0.001). Peak quadriceps force and average hamstring force decreased, whereas gastrocnemius and soleus muscle forces increased when running with a forefoot strike (P < 0.05). Knee flexion angle at initial contact increased (P < 0.001), total knee excursion decreased (P < 0.001), and no change occurred in peak knee flexion angle (P = 0.238). Step length did not change between conditions (P = 0.375), but the leading leg landed with the foot positioned with a horizontal distance closer to the hip at initial contact in the forefoot strike condition (P < 0.001). Conclusions: Altering one's strike pattern to a forefoot strike results in consistent reductions in patellofemoral joint stress independent of changes in step length. Thus, implementation of forefoot strike training programs may be warranted in the treatment of runners with patellofemoral pain. However, it is suggested that the transition to a forefoot strike pattern should be completed in a graduated manner.
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Synopsis: This clinical commentary discusses the mechanisms used by the lower-limb musculature to achieve faster running speeds. A variety of methodological approaches have been taken to evaluate lower-limb muscle function during running, including direct recordings of muscle electromyographic signal, inverse dynamics-based analyses, and computational musculoskeletal modeling. Progressing running speed from jogging to sprinting is mostly dependent on ankle and hip muscle performance. For speeds up to approximately 7.0 m/s, the dominant strategy is to push on the ground forcefully to increase stride length, and the major ankle plantar flexors (soleus and gastrocnemius) have a particularly important role in this regard. At speeds beyond approximately 7.0 m/s, the force-generating capacity of these muscles becomes less effective. Therefore, as running speed is progressed toward sprinting, the dominant strategy shifts toward the goal of increasing stride frequency and pushing on the ground more frequently. This strategy is achieved by generating substantially more power at the hip joint, thereby increasing the biomechanical demand on proximal lower-limb muscles such as the iliopsoas, gluteus maximus, rectus femoris, and hamstrings. Basic science knowledge regarding lower-limb muscle function during running has implications for understanding why sprinting performance declines with age. It is also of great value to the clinician for designing rehabilitation programs to restore running ability in young, previously active adults who have sustained a traumatic brain injury and have severe impairments of muscle function (eg, weakness, spasticity, poor motor control) that limit their capacity to run at any speed.
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Purpose: Knee pain and Achilles tendinopathies are the most common complaints among runners. The differences in the running mechanics may play an important role in the pathogenesis of lower limb overuse injuries. However, the effect of a runner's foot strike pattern on the ankle and especially on the knee loading is poorly understood. The purpose of this study was to examine whether runners using a forefoot strike pattern exhibit a different lower limb loading profile than runners who use rearfoot strike pattern. Methods: Nineteen female athletes with a natural forefoot strike (FFS) pattern and pair-matched women with rearfoot strike (RFS) pattern (n = 19) underwent 3-D running analysis at 4 m·s⁻¹. Joint angles and moments, patellofemoral contact force and stresses, and Achilles tendon forces were analyzed and compared between groups. Results: FFS demonstrated lower patellofemoral contact force and stress compared with heel strikers (4.3 ± 1.2 vs 5.1 ± 1.1 body weight, P = 0.029, and 11.1 ± 2.9 vs 13.0 ± 2.8 MPa, P = 0.04). In addition, knee frontal plane moment was lower in the FFS compared with heel strikers (1.49 ± 0.51 vs 1.97 ± 0.66 N·m·kg⁻¹, P =0.015). At the ankle level, FFS showed higher plantarflexor moment (3.12 ± 0.40 vs 2.54 ± 0.37 N·m·kg⁻¹; P = 0.001) and Achilles tendon force (6.3 ± 0.8 vs 5.1 ± 1.3 body weight; P = 0.002) compared with RFS. Conclusions: To our knowledge, this is the first study that shows differences in patellofemoral loading and knee frontal plane moment between FFS and RFS. FFS exhibit both lower patellofemoral stress and knee frontal plane moment than RFS, which may reduce the risk of running-related knee injuries. On the other hand, parallel increase in ankle plantarflexor and Achilles tendon loading may increase risk for ankle and foot injuries.
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The lengths and velocities of muscle fibers have a dramatic effect on muscle force generation. It is unknown, however, whether the lengths and velocities of lower limb muscle fibers substantially affect the ability of muscles to generate force during walking and running. We examined this issue by developing simulations of muscle-tendon dynamics that calculate the lengths and velocities of muscle fibers from electromyographic recordings of eleven lower limb muscles and kinematic measurements of the hip, knee, and ankle made as five subjects walked at speeds of 1.0-1.75 m/s and ran at speeds of 2.0-5.0 m/s. We analyzed the simulated fiber lengths, fiber velocities, and forces to evaluate the influence of force-length and force-velocity properties on force generation at different walking and running speeds. The simulations revealed that force generation ability (i.e., the force generated per unit of activation) of eight of the eleven muscles was significantly affected by walking or running speed. Soleus force generation ability decreased with increasing walking speed, but the transition from walking to running increased the force generation ability by reducing fiber velocities. Our results demonstrate the influence of soleus muscle architecture on the walk-to-run transition and the effects of muscle-tendon compliance on the plantarflexors' ability to generate ankle moment and power. The study presents data that permit lower limb muscles to be studied in unprecedented detail by relating muscle fiber dynamics and force generation to the mechanical demands of walking and running.
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Abstract The present study aimed to quantify the intensity of lower extremity plyometric exercises by determining joint mechanical output. Ten men (age, 27.3 ± 4.1 years; height, 173.6 ± 5.4 cm; weight, 69.4 ± 6.0 kg; 1-repetition maximum [1RM] load in back squat 118.5 ± 12.0 kg) performed the following seven plyometric exercises: two-foot ankle hop, repeated squat jump, double-leg hop, depth jumps from 30 and 60 cm, and single-leg and double-leg tuck jumps. Mechanical output variables (torque, angular impulse, power, and work) at the lower limb joints were determined using inverse-dynamics analysis. For all measured variables, ANOVA revealed significant main effects of exercise type for all joints (P < 0.05) along with significant interactions between joint and exercise (P < 0.01), indicating that the influence of exercise type on mechanical output varied among joints. Paired comparisons revealed that there were marked differences in mechanical output at the ankle and hip joints; most of the variables at the ankle joint were greatest for two-foot ankle hop and tuck jumps, while most hip joint variables were greatest for repeated squat jump or double-leg hop. The present results indicate the necessity for determining mechanical output for each joint when evaluating the intensity of plyometric exercises.
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This study tests if running economy differs in minimal shoes versus standard running shoes with cushioned elevated heels and arch supports and in forefoot versus rearfoot strike gaits. We measured the cost of transport (mL O(2)·kg(-1)·m(-1)) in subjects who habitually run in minimal shoes or barefoot while they were running at 3.0 m·s(-1) on a treadmill during forefoot and rearfoot striking while wearing minimal and standard shoes, controlling for shoe mass and stride frequency. Force and kinematic data were collected when subjects were shod and barefoot to quantify differences in knee flexion, arch strain, plantar flexor force production, and Achilles tendon-triceps surae strain. After controlling for stride frequency and shoe mass, runners were 2.41% more economical in the minimal-shoe condition when forefoot striking and 3.32% more economical in the minimal-shoe condition when rearfoot striking (P < 0.05). In contrast, forefoot and rearfoot striking did not differ significantly in cost for either minimal- or standard-shoe running. Arch strain was not measured in the shod condition but was significantly greater during forefoot than rearfoot striking when barefoot. Plantar flexor force output was significantly higher in forefoot than in rearfoot striking and in barefoot than in shod running. Achilles tendon-triceps surae strain and knee flexion were also lower in barefoot than in standard-shoe running. Minimally shod runners are modestly but significantly more economical than traditionally shod runners regardless of strike type, after controlling for shoe mass and stride frequency. The likely cause of this difference is more elastic energy storage and release in the lower extremity during minimal-shoe running.
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Although the biomechanical properties of the various types of running foot strike (rearfoot, midfoot, and forefoot) have been studied extensively in the laboratory, only a few studies have attempted to quantify the frequency of running foot strike variants among runners in competitive road races. We classified the left and right foot strike patterns of 936 distance runners, most of whom would be considered of recreational or sub-elite ability, at the 10 km point of a half-marathon/marathon road race. We classified 88.9% of runners at the 10 km point as rearfoot strikers, 3.4% as midfoot strikers, 1.8% as forefoot strikers, and 5.9% of runners exhibited discrete foot strike asymmetry. Rearfoot striking was more common among our sample of mostly recreational distance runners than has been previously reported for samples of faster runners. We also compared foot strike patterns of 286 individual marathon runners between the 10 km and 32 km race locations and observed increased frequency of rearfoot striking at 32 km. A large percentage of runners switched from midfoot and forefoot foot strikes at 10 km to rearfoot strikes at 32 km. The frequency of discrete foot strike asymmetry declined from the 10 km to the 32 km location. Among marathon runners, we found no significant relationship between foot strike patterns and race times.
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An understanding of hamstring mechanics during sprinting is important for elucidating why these muscles are so vulnerable to acute strain-type injury. The purpose of this study was twofold: first, to quantify the biomechanical load (specifically, musculotendon strain, velocity, force, power, and work) experienced by the hamstrings across a full stride cycle; and second, to determine how these parameters differ for each hamstring muscle (i.e., semimembranosus (SM), semitendinosus (ST), biceps femoris long head (BF), biceps femoris short head (BF)). Full-body kinematics and ground reaction force data were recorded simultaneously from seven subjects while sprinting on an indoor running track. Experimental data were integrated with a three-dimensional musculoskeletal computer model comprised of 12 body segments and 92 musculotendon structures. The model was used in conjunction with an optimization algorithm to calculate musculotendon strain, velocity, force, power, and work for the hamstrings. SM, ST, and BF all reached peak strain, produced peak force, and formed much negative work (energy absorption) during terminal swing. The biomechanical load differed for each hamstring muscle: BF exhibited the largest peak strain, ST displayed the greatest lengthening velocity, and SM produced the highest peak force, absorbed and generated the most power, and performed the largest amount of positive and negative work. As peak musculotendon force and strain for BF, ST, and SM occurred around the same time during terminal swing, it is suggested that this period in the stride cycle may be when the biarticular hamstrings are at greatest injury risk. On this basis, hamstring injury prevention or rehabilitation programs should preferentially target strengthening exercises that involve eccentric contractions performed with high loads at longer musculotendon lengths.
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Knowledge regarding the biomechanical function of the lower limb muscle groups across a range of running speeds is important in improving the existing understanding of human high performance as well as in aiding in the identification of factors that might be related to injury. The purpose of this study was to evaluate the effect of running speed on lower limb joint kinetics. Kinematic and ground reaction force data were collected from eight participants (five males and three females) during steady-state running on an indoor synthetic track at four discrete speeds: 3.50±0.04, 5.02±0.10, 6.97±0.09, and 8.95±0.70 m·s. A standard inverse-dynamics approach was used to compute three-dimensional torques at the hip, knee, and ankle joints, from which net powers and work were also calculated. A total of 33 torque, power, and work variables were extracted from the data set, and their magnitudes were statistically analyzed for significant speed effects. The torques developed about the lower limb joints during running displayed identifiable profiles in all three anatomical planes. The sagittal-plane torques, net powers, and work done at the hip and knee during terminal swing demonstrated the largest increases in absolute magnitude with faster running. In contrast, the work done at the knee joint during stance was unaffected by increasing running speed, whereas the work done at the ankle joint during stance increased when running speed changed from 3.50 to 5.02 m·s, but it appeared to plateau thereafter. Of all the major lower limb muscle groups, the hip extensor and knee flexor muscles during terminal swing demonstrated the most dramatic increase in biomechanical load when running speed progressed toward maximal sprinting.
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This review describes how computational modeling can be combined with noninvasive gait measurements to describe and explain muscle and joint function in human locomotion. Five muscles--the gluteus maximus, gluteus medius, vasti, soleus, and gastrocnemius--contribute most significantly to the accelerations of the center of mass in the vertical, fore-aft, and medio-lateral directions when humans walk and run at their preferred speeds. Humans choose to switch from a walk to a run at speeds near 2 m s(-1) to enhance the biomechanical performance of the ankle plantarflexors and to improve coordination of the knee and ankle muscles during stance. Muscles that do not span a joint can contribute to the contact force transmitted by that joint and therefore affect its stability. In walking, for example, uniarticular muscles that cross the hip and ankle act to create the adduction moment at the knee, thereby contributing to the contact force present in the medial compartment.
Article
Running speed is limited by a mechanical interaction between the stance and swing phases of the stride. Here, we tested whether stance phase limitations are imposed by ground force maximums or foot-ground contact time minimums. We selected one-legged hopping and backward running as experimental contrasts to forward running and had seven athletic subjects complete progressive discontinuous treadmill tests to failure to determine their top speeds in each of the three gaits. Vertical ground reaction forces [in body weights (W(b))] and periods of ground force application (T(c); s) were measured using a custom, high-speed force treadmill. At top speed, we found that both the stance-averaged (F(avg)) and peak (F(peak)) vertical forces applied to the treadmill surface during one-legged hopping exceeded those applied during forward running by more than one-half of the body's weight (F(avg) = 2.71 +/- 0.15 vs. 2.08 +/- 0.07 W(b); F(peak) = 4.20 +/- 0.24 vs. 3.62 +/- 0.24 W(b); means +/- SE) and that hopping periods of force application were significantly longer (T(c) = 0.160 +/- 0.006 vs. 0.108 +/- 0.004 s). Next, we found that the periods of ground force application at top backward and forward running speeds were nearly identical, agreeing to within an average of 0.006 s (T(c) = 0.116 +/- 0.004 vs. 0.110 +/- 0.005 s). We conclude that the stance phase limit to running speed is imposed not by the maximum forces that the limbs can apply to the ground but rather by the minimum time needed to apply the large, mass-specific forces necessary.
Article
The telemetered electromyographic (EMG) activity of quadriceps, hamstrings, triceps surae and pretibial muscles on the affected side of 20 adult hemiplegic subjects was examined during locomotion. The subjects ranged in age from 29 to 68 years (mean, 52.1). Duration of the lesions ranged from 1 month to 8 years: in 11 subjects the duration of the lesions ranged from 1 to 9 months (mean, 4.9 months), and in the remaining 9 subjects from 1 to 8 years (mean, 4 years 2 months). Shoes with five microswitches, two in the heel and three in the sole, were used to correlate the EMG activity with eight specific components of the gait cycle. The results of the study showed a loss of the phasic pattern associated with normal locomotion. The hemiplegic subjects showed the greatest activity in the period of midstance. Expressed as a percentage of the total cycle, the mean stance time of the paretic lower limb was 67% and the mean swing time was 33%. The unaffected lower limb showed a stance phase of 80% and a swing phase of 20%.
Article
The telemetered electromyographic (EMG) activity of pretibial muscles (tibialis anterior), triceps surae (lateral gastrocnemius), medial hamstring group and quadriceps (vastus lateralis) of 20 normal subjects was examined during locomotion. The ages of the subjects ranged from 8 to 72 years (mean, 37 years). A microswitch shoe was used to correlate the EMG activity with eight specific components of the gait cycle. Tibialis anterior showed two peaks of activity, the first at the swing-stance transition, the second at the stance-swing transition. Gastrocnemius showed a single peak of activity recorded during push-off. The medial hamstring showed its greatest activity during deceleration in the swing phase. Vastus lateralis demonstrated peak activity at the transition from swing to stance. The mean cadence was 106 steps per minute. Swing phase occupied 39.6% and stance phase 60.4% of the gait cycle.
Article
The function and mechanical behaviour of human skeletal muscle are in many ways unknown during natural locomotion. To gain more insight into these questions a method was developed to record directly in vivo forces from the human Achilles tendon (AT). The paper focuses on the details of the various techniques including the design, surgical implantation and calibration of the transducers. The implantation is performed under local anaesthesia and the measurements can last up to three hours, after which the transducer is removed. Exemplar results are presented from the measurements during walking, running and jumping. The loading of AT reached in some cases values as high as 9 KN, corresponding to 12.5 times the body weight or, when expressed per cross-sectional area of the tendon, the value was 11,100 N cm-2. During the early contact phase of running the rate of AT force development increased linearly with the increase of running speed. Indirect measurements of the length changes of the muscle-tendon complex was used to plot the force-length and force-velocity relationships in the various activity situations. The observed results demonstrated that in normal locomotion involving the stretch-shortening cycle (SSC) muscle actions, the mechanical response of the triceps surae muscle is very different from the classical curves obtained in isolated muscle preparations. In agreement with the animal experiments using a similar in vivo technique, the natural locomotion with primarily SSC actions may produce muscle outputs which can be very different from the various conditions of the isolated preparations, where activation levels are held constant and storage and utilization of strain energy is limited. It is suggested that despite some limitations (due to e.g. difficulties in obtaining volunteers for AT force measurements, possible inaccuracies in transducer calibration and in muscle length estimates) the in vivo force measurement technique has an important role in studying the mechanical behaviour of muscle and its control under normal movement conditions.
Article
A model of the lower extremity was created and analyzed to estimate the magnitude of the loads at common injury sites during running and the proportions due to muscle and ground reaction forces. The range of peak loads, normalized to subject body weight (BW), estimated from five running trials were: (1) Achilles tendon force: 6.1-8.2 BW; (2) ankle bone-on-bone--compressive force: 10.3-14.1 BW; shear force: -0.4- -0.7 BW; (3) lower leg--compressive force: 10.3-14.1 BW; shear force: -0.4- -0.7 BW; bending moment: -85- -117 N.m; (4) patellar tendon force: 4.7-6.9 BW; (5) patello-femoral joint compressive force: 7.0-11.1 BW; (6) plantar fascia force: 1.3-2.9 BW. All peak loads were associated with mid-stance and push-off when muscle activity was maximal. The impact force at heel contact was estimated to have no effect on the peak force seen at the chronic injury sites. The plantarflexor muscles were shown to provide an anti-shear mechanism at the ankle and an anti-shear, anti-bending mechanism within the lower leg. Simple sensitivity analyses were performed on the models to display possible variability in the peak load estimates.
Article
Reported specific tension measurements for human skeletal muscle vary widely. This variability could be due, at least in part, to the determination of the physiological cross-sectional area (PCSA) of the muscles. In the present study, serial magnetic resonance images were taken every 10 mm along the lower leg of 8 male subjects to calculate the volume and subsequently the PCSAs of the individual muscles producing plantar flexor and dorsiflexor torques. Maximum plantar flexor and dorsiflexor voluntary isometric torques were determined at ankle joint angles of 90, 100, 110, and 120 degrees. Peak tendon force estimated from torque and moment arm measurements was more than fourfold higher in the plantar flexors (3,623 +/- 136 N) than in the dorsiflexors (832 +/- 19 N). PCSAs were about eight- and threefold higher than the anatomic cross-sectional areas at the level of maximum girth of the calf for the plantar flexor and dorsiflexor groups, respectively. Mean muscle volume and PCSA were 4.6 and 12 times larger in the plantar flexors compared with the dorsiflexors, respectively. The PCSAs of both plantar flexors (r = 0.92) and dorsiflexors (r = 0.80) were highly correlated with the tendon tension of the respective muscle groups. The maximum specific tension was more than twofold higher in dorsiflexors than in plantar flexors. These data suggest that factors other than PCSA contribute to the force output potential of ankle plantar flexors and dorsiflexors in humans.
Article
Rising from a chair is a task essential for independent living. Many elderly persons have difficult with this task. Previous studies have drawn conflicting conclusions as to the role of strength in limiting the ability to rise from a chair. The purpose of this study is to determine the role of knee extensor strength in rising from a chair in the functionally impaired elderly. It is hypothesized that knee extensor strength limits the minimum chair height from which a subject can rise in the functionally impaired elderly, but not in the young. Studying both young healthy adults and functionally impaired elderly showed that required joint moment increased monotonically with decreasing chair height. Further, the elderly used significantly more of their available strength to rise from any chair height, and their mean required knee moment was 97% of the available strength when rising from the lowest chair height from which they could successfully rise. These data suggest that strength is a limiting factor in determining the minimum chair height from which the functionally impaired elderly may rise.
Article
We twice tested the hypothesis that top running speeds are determined by the amount of force applied to the ground rather than how rapidly limbs are repositioned in the air. First, we compared the mechanics of 33 subjects of different sprinting abilities running at their top speeds on a level treadmill. Second, we compared the mechanics of declined (-6 degrees ) and inclined (+9 degrees ) top-speed treadmill running in five subjects. For both tests, we used a treadmill-mounted force plate to measure the time between stance periods of the same foot (swing time, t(sw)) and the force applied to the running surface at top speed. To obtain the force relevant for speed, the force applied normal to the ground was divided by the weight of the body (W(b)) and averaged over the period of foot-ground contact (F(avge)/W(b)). The top speeds of the 33 subjects who completed the level treadmill protocol spanned a 1.8-fold range from 6.2 to 11.1 m/s. Among these subjects, the regression of F(avge)/W(b) on top speed indicated that this force was 1.26 times greater for a runner with a top speed of 11.1 vs. 6.2 m/s. In contrast, the time taken to swing the limb into position for the next step (t(sw)) did not vary (P = 0.18). Declined and inclined top speeds differed by 1.4-fold (9.96+/-0.3 vs. 7.10+/-0.3 m/s, respectively), with the faster declined top speeds being achieved with mass-specific support forces that were 1.3 times greater (2.30+/- 0.06 vs. 1.76+/-0.04 F(avge)/ W(b)) and minimum t(sw) that were similar (+8%). We conclude that human runners reach faster top speeds not by repositioning their limbs more rapidly in the air, but by applying greater support forces to the ground.
Article
An understanding of landing techniques is important for the prevention of injuries in a number of athletic events. There is a risk of injury to the ankle during landings, and the kinematics and forces involved in different landing strategies may be related to the occurrence of trauma. In the current study, four drop conditions from a 30.48-cm (12-inch) height were tested. The conditions were a) BN: Bent knee (self-selected), Natural (self-selected) plantar flexor contraction; b) SN: Stiff-knee, Natural plantar flexors; c) SP: Stiff-knee, Plantar flexors absorbing the impact; and d) SH: Stiff-knee, absorbing most of the impact in the Heels. Peak vertical forces and accelerations were measured, and Achilles tendon forces and stiffnesses were calculated. Peak vertical forces and peak tibial accelerations were highest for the SH condition (2418 N and 20.7 G), whereas peak Achilles tendon force was highest for SP drops. The overall average AT stiffness was 166,345 N x m(-1). The results from the study were used in an extensive cadaver study to investigate ankle injuries. The data from the current study indicate that athletes may not use their full energy absorbing potential in landings during sporting activities.
Article
We investigated force enhancement following stretching in the in situ cat soleus muscle on the ascending and descending limb of the force-length relationship by varying the amount and speed of stretching and the frequency of activation (5 Hz, 30 Hz). There was a small but consistent (P<0.05) amount of force enhancement following muscle stretching on the ascending limb of the force-length relationship for both stimulation frequencies. The steady-state active isometric forces following stretches of 9 mm on the descending limb of the force-length relationship were always equal to or greater than the corresponding forces from the purely isometric contractions at the length at which the stretch was started. Therefore, force production for these trials showed positive stiffness and was associated with stable behavior. Following active stretching of cat soleus on the descending limb of the force-length relationship, the passive forces at the end of the test were significantly greater than the corresponding passive forces for purely isometric contractions, or the passive forces following stretching of the passive muscle. This passive force enhancement following active stretching increased with increasing magnitude of stretch, was not associated with structural damage, and only disappeared once the muscle was shortened. For stretches of 6 mm and 9 mm, the passive force enhancement accounted for more than 50 % of the total force enhancement, reaching a peak contribution of 83.7 % for the stretches of 9 mm at a speed of 3 mm s(-1). The results of this study suggest that a passive structural element provides a great part of the force enhancement on the descending limb of the force-length relationship of the cat soleus. Furthermore, the results indicate that mechanisms other than sarcomere length non-uniformity alone are operative.
Article
To determine whether individuals with patellofemoral pain (PFP) demonstrate elevated patellofemoral joint (PFJ) stress compared with pain-free controls during free and fast walking. A cross-sectional study utilizing an experimental and a control group. Although the cause of PFJ pathology is believed to be related to elevated joint stress (force per unit area), this hypothesis has not been adequately tested and causative mechanisms have not been clearly defined. Ten subjects with a diagnosis of PFP and 10 subjects without pain participated. All subjects completed two phases of data collection: 1) magnetic resonance imaging (MRI) assessment to determine PFJ contact area and 2) comprehensive gait analysis during self-selected free and fast walking velocities. Data obtained from both phases were required as input variables into a biomechanical model to quantify PFJ stress. On the average, PFJ stress was significantly greater in subjects with PFP compared with control subjects during level walking. The observed increase in PFJ stress in the PFP group was attributed to a significant reduction in PFJ contact area, as the PFJ reaction forces were similar between groups. Our results are consistent with the hypothesis that increased patellofemoral joint stress may be a predisposing factor with respect to development of PFP. Clinically, these findings indicate that treatments designed to increase the area of contact between the patella and the femur may be beneficial in reducing the PFJ stress during functional activities. Patellofemoral pain affects about 25% of the population, yet its etiology is unknown. Knowledge of the biomechanical factors contributing to patellofemoral joint pain may improve treatment techniques and guide development of prevention strategies.
Article
The purpose of this study was to examine two hypotheses: (a) during voluntary and electrically induced isometric contractions the moments measured at the dynamometer are different from the resultant moments in the same plane around the ankle joint and (b) at a given resultant moment during electrically induced isometric contractions the ankle angle while loading is different from the ankle angle while unloading. Twenty-seven long distance runners participated in the study. All subjects performed isometric maximal voluntary contractions (MVC) and contractions induced by electrostimulation at four different ankle-knee angle combinations on a Biodex-dynamometer. The kinematics of the leg were recorded using the vicon 624 system with eight cameras operating at 120 Hz. The main findings were: (a) the resultant moment at the ankle joint and the moment measured by the Biodex-dynamometer during isometric contractions are different, (b) during a plantar flexion effort the ankle angle changes significantly, whereas the knee angle shows only small and in most cases not significant changes, and (c) at identical resultant ankle joint moments the ankle angles are different between the loading and the unloading phases. The observed differences may lead to erroneous conclusions concerning the following: (a) diagnostic of muscle architecture, (b) estimation of the moment-ankle angle relationship and (c) estimation of the strain and hysteresis of tendons and aponeuroses.
Article
Electromyographic (EMG) activity of the leg muscles and the ground reaction forces were recorded in 17 elite male middle-distance runners, who performed isometric maximal voluntary contractions (MVC) as well as running at different speeds. Electromyograms were recorded from the gluteus maximus, vastus lateralis, biceps femoris, gastrocnemius and tibialis anterior. The results indicated that the averaged EMG (aEMG) activities of all the muscles studied increased (P < 0.05) with increasing running speed, especially in the pre-contact and braking phases. At higher speeds, the aEMG activities of the gastrocnemius, vastus lateralis, biceps femoris and gluteus maximus exceeded 100% MVC in these same phases. These results suggest that maximal voluntary contractions cannot be used as an indicator of the full activation potential of human skeletal muscle. Furthermore, the present results suggest that increased pre-contact EMG potentiates the functional role of stretch reflexes, which subsequently increases tendomuscular stiffness and enhances force production in the braking and/or propulsive phases in running. Furthermore, a more powerful force production in the optimal direction for increasing running speed effectively requires increased EMG activity of the two-joint muscles (biceps femoris, rectus femoris and gastrocnemius) during the entire running cycle.