Article

Comparison of MRI with EMG to study muscle activity associated with dynamic plantar flexion

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Abstract

This study compared magnetic resonance imaging (MRI) and surface electromyography (EMG) to evaluate the effect of knee angle upon plantar flexion activity in the triceps surae muscles [medial & lateral gastrocnemius (MG, LG) and the soleus (SOL)]. Two weight & height matched groups performed identical protocols, twelve (6M, 6F) in the MRI group, twelve (8M, 4F) in the EMG group. Subjects plantar flexed dynamically for 2 min at 25% of 1-repetition maximum voluntary contraction (1-RM). Exercise was performed with the knee extended (0 degrees flexion), flexed (90 degrees ), and partially flexed (45 degrees ). In the MRI group spin-echo images were acquired before and immediately following each exercise session. T(2) times, calculated at rest and after exercise by fitting the echoes to a monoexponential decay pattern with a least-squares algorithm, were compared with EMG data. In the EMG group a bipolar electrode was used to collect samples were from the MG, LG, SOL, and anterior tibialis (TA) during exercise at each knee angle, MRI also examined the peroneus (PER). At 0 degrees flexion MRI demonstrated a significant post-exercise T(2) increase in the MG (p < or = 0.001), LG (p < or = 0.001), and PER (p < or = 0.01), with no T(2) change in the SOL or TA. At 90 degrees flexion there was a significant T(2) increase in the SOL (p < or = 0.001) with no significant T(2) change in the MG, LG, PER, or TA. At 45 degrees T(2) increased significantly in the SOL (p < or = 0.001) and LG (p < or = 0.05), but not the MG, PER, or TA. EMG produced similar results with the exception that there was significant activity in the TA during the relaxation cycle of the 90 degrees protocol. We conclude that: 1) Soleus activity is measurable by MRI; and 2) MRI and EMG produce similar results from different physiological sources, and are therefore complementary tools for evaluating muscle activity.

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... Consequently, the MG has a greater force-producing capacity than the LG or Sol. Our results are corroborated by data reported for ankle plantar flexor exercise, in which the MG showed higher iEMG (19,28,36,37) and T2 values (4,19,28,42) than the LG and Sol at several workload settings. We therefore conclude that the relative areas of activation differ among TS muscles during our exercise protocol. ...
... Consequently, the MG has a greater force-producing capacity than the LG or Sol. Our results are corroborated by data reported for ankle plantar flexor exercise, in which the MG showed higher iEMG (19,28,36,37) and T2 values (4,19,28,42) than the LG and Sol at several workload settings. We therefore conclude that the relative areas of activation differ among TS muscles during our exercise protocol. ...
... Fortunately, fiber types and their distributions in human muscles do not dramatically compare with those in the corresponding muscles of rodents and other quadrupeds (33), Therefore, Prior et al. (30) concluded that semiquantitative comparisons among muscles can be justified irrespective of fiber type. In fact, human TS muscles have frequently been used in studies in which mfMRI was used to measure muscle activation (4,19,28,42). ...
Article
The purposes of this study were 1) to quantify the volume of activated parts within a whole muscle and 2) to examine activated area distributions along the length of muscle. Seven male subjects performed five sets of 10 repetitions of a single-leg calf-raise exercise with the knee fully extended. Transverse relaxation time (T2)-weighted spin echo images were acquired before and immediately after the exercise. A range of pixels with a T2 greater than the mean +1 SD of the region of interest (ROI) from the preexercise image and pixels with a T2 lower than the mean + SD of the ROI from the postexercise image were defined as "active" muscle. The active muscle images were three dimensionally reconstructed, from which the volume of the activated muscle was determined for individual triceps surae (TS) muscles. Our data indicate that approximately 46% of the medial gastrocnemius (MG) muscle was activated during the exercise, with activation of the lateral gastrocnemius (LG) and soleus (Sol) muscles being approximately 35%. In the MG, distal portions had a greater percentage area of activated muscle than the proximal portions (P < 0.05), which was consistent with the results regarding electromyogram activity. In contrast, regional activation differences were not observed in the LG and Sol. These findings suggest that the amounts of activated muscle and its distribution would be different among TS muscles.
... In neurophysiology, the generally accepted order of recruitment proposes that the type-I endurance fibres, smaller motor units, and smaller motor neurons of soleus are recruited more readily at lower intensities of plantar-flexion (Henneman, Somjen, & Carpenter, 1965;Mendell, 2005;Milner-Brown, Stein, & Yemm, 1973;Tucker & Tü rker, 2004;Winter, 2005). The literature demonstrates that recruitment of gastrocnemius intensifies as plantar-flexion effort, mechanical demand or load increases (McGowan, Neptune, & Kram, 2008;Price et al., 2003). The overall motor recruitment of the triceps surae muscles is influenced by nerve and fibre morphology, central modulation, and training (Basmajian & Deluca, 1985;Fleck & Kraemer, 1997;Noakes, 2003). ...
... As gastrocnemius is bi-articular and soleus mono-articular, variation of the knee angle on a fixed ankle will selectively alter the length and subsequent function of gastrocnemius (Table 1). A reduction in plantar-flexion force is observed in knee flexion and is mainly attributed to the shortening and decreased mechanical advantage of gastrocnemius (Price et al., 2003). ...
... The antagonists are also important in plantar-flexion function (Benjamin Toumi, Ralphs, Bydder, Best, & Milz, 2006;Maganaris, Narici, Almekinders, & Maffulli, 2004;Tucker et al., 2005;Windhorst, 2007) and become increasingly influential as plantar-flexors fatigue (Patikas et al., 2002). Although the extent to which the synergists and antagonists affect the overall performance of the triceps surae is debated (Magnusson, Aagaard, Rosager, Dyhre-Poulsen, & Kjaer, 2001;Price et al., 2003;Segal & Song, 2005;Wakahara, Kanehisa, Kawakami, & Fukunaga, 2008), the literature demonstrates that an increase in their activation is a sign of triceps surae muscle fatigue (Patikas et al., 2002), is frequently expressed through compensatory movements (Clarkson, 2000;Magee, 2008;Palmer, 1998) and advocates CRT termination. Since fatigue is also governed by many psychosocial factors (Dutton, 2008), it may be difficult to distinguish between ''neuro-physiological'' and ''psychological'' (lack of motivation or pain) fatigue. ...
Article
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Athletes commonly sustain injuries to the triceps surae muscle-tendon unit. The calf-raise test (CRT) is frequently employed in sports medicine for the detection and monitoring of such injuries. However, despite being widely-used, a recent systematic review found no universal consensus relating to the test's purpose, parameters, and standard protocols. The purpose of this paper is to provide a clinical perspective on the anatomo-physiological bases underpinning the CRT and to discuss the utilisation of the test in relation to the structure and function of the triceps surae muscle-tendon unit. Structured narrative review. Nine electronic databases were searched using keywords and MESH headings related to the CRT and the triceps surae muscle-tendon unit anatomy and physiology. A hand-search of reference lists and relevant journals and textbooks complemented the electronic search. There is evidence supporting the clinical use of the CRT to assess soleus and gastrocnemius, their shared aponeurosis, the Achilles tendon, and the combined triceps surae muscle-tendon unit. However, employing the same clinical test to assess all these structures and their associated functions remains challenging. Further refinement of the CRT for the triceps surae muscle-tendon unit is needed. This is vital to support best practice utilisation, standardisation, and interpretation of the CRT in sports medicine.
... 16,17 Such localization cannot distinguish between muscle groups that are recruited differently in the performed exercise (e.g. soleus (SOL) and gastrocnemius during plantar flexion [18][19][20][21][22][23] ). ...
... The knee of the volunteers was fully extended during the dynamic examination (2 min rest, 6 min exercise and 6 min recovery) to ensure a major involvement of the gastrocnemius muscles and only a minor contribution of the SOL muscle to the exercise performed. [20][21][22] The volunteers performed plantar flexions at a workload set to about 25-35% of the maximal voluntary contraction force, once every T R (2 s). The exercise was synchronized with the data acquisition based on an audio signal, so that the MRSI data were acquired when the calf muscle was relaxed. ...
... In this leg position the SOL muscle is expected to be involved more than the two gastrocnemii. 20 This second examination was performed at least 20 min after the first one, to ensure sufficient metabolic recovery. 36 Two additional spiral-MRSI measurements were performed at rest in two of these subjects in order to acquire representative flip angle maps 37 ...
Article
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Phosphorus MRSI (³¹P–MRSI) using a spiral‐trajectory readout at 7 T was developed for high temporal resolution mapping of the mitochondrial capacity of exercising human skeletal muscle. The sensitivity and localization accuracy of the method was investigated in phantoms. In vivo performance was assessed in 12 volunteers, who performed a plantar flexion exercise inside a whole‐body 7 T MR scanner using an MR‐compatible ergometer and a surface coil. In five volunteers the knee was flexed (~60°) to shift the major workload from the gastrocnemii to the soleus muscle. Spiral‐encoded MRSI provided 16–25 times faster mapping with a better point spread function than elliptical phase‐encoded MRSI with the same matrix size. The inevitable trade‐off for the increased temporal resolution was a reduced signal‐to‐noise ratio, but this was acceptable. The phosphocreatine (PCr) depletion caused by exercise at 0° knee angulation was significantly higher in both gastrocnemii than in the soleus (i.e. 64.8 ± 19.6% and 65.9 ± 23.6% in gastrocnemius lateralis and medialis versus 15.3 ± 8.4% in the soleus). Spiral‐encoded ³¹P–MRSI is a powerful tool for dynamic mapping of exercising muscle oxidative metabolism, including localized assessment of PCr concentrations, pH and maximal oxidative flux with high temporal and spatial resolution.
... Soleus is connected to the tibia and gastrocnemius lateralis and medialis originate at the femur; therefore changes of the knee angle affect these muscles to a different extent. 15,16 Additionally, the fibre-type composition differs between these calf muscles: soleus is predominantly composed of slow twitch fibres (80 %), while a more even distribution of slow and fast twitch fibres has been reported in gastrocnemius. 17,18 Because of these biomechanical and anatomical differences, the knee angle is a crucial parameter determining the distribution of workload between calf muscles during plantar flexion exercise. ...
... 19 Previous studies have shown that soleus is more activated with a flexed knee, while gastrocnemius contributes more with an extended knee. Price et al 16 used MRI and surface electromyography to study the pre-versus post-exercise changes of T 2 and electromyography activity in two groups of 12 subjects exercising at three different knee angles. Valkovic et al 20 acquired dynamic spiral spectroscopic 31 P magnetic resonance (MR) images in five volunteers performing plantar flexion with two different knee angles. ...
... To maintain a coherent exercise protocol, the same force was chosen for all knee angles (similar to Price et al 16 ). This resulted in an exercise response for gastrocnemius that can be explained consistently as decreasing recruitment with a bent knee. ...
Article
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Exercise studies investigating the metabolic response of calf muscles using ³¹P MRS are usually performed with a single knee angle. However, during natural movement, the distribution of workload between the main contributors to force, gastrocnemius and soleus is influenced by the knee angle. Hence, it is of interest to measure the respective metabolic response of these muscles to exercise as a function of knee angle using localized spectroscopy. Time‐resolved multivoxel ³¹P MRS at 7 T was performed simultaneously in gastrocnemius medialis and soleus during rest, plantar flexion exercise and recovery in 12 healthy volunteers. This experiment was conducted with four different knee angles. PCr depletions correlated negatively with knee angle in gastrocnemius medialis, decreasing from 79±14 % (extended leg) to 35±23 %(∼40°), and positively in soleus, increasing from 20±21 % to 36±25 %; differences were significant. Linear correlations were found between knee angle and end‐exercise PCr depletions in gastrocnemius medialis (R²=0.8) and soleus (R²=0.53). PCr recovery times and end‐exercise pH changes that correlated with PCr depletion were consistent with the literature in gastrocnemius medialis and differences between knee angles were significant. These effects were less pronounced in soleus and not significant for comparable PCr depletions. Maximum oxidative capacity calculated for all knee angles was in excellent agreement with the literature and showed no significant changes between different knee angles. In conclusion, these findings confirm that plantar flexion exercise with a straight leg is a suitable paradigm, when data are acquired from gastrocnemius only (using either localized MRS or small surface coils), and that activation of soleus requires the knee to be flexed. The present study comprises a systematic investigation of the effects of the knee angle on metabolic parameters, measured with dynamic multivoxel ³¹P MRS during muscle exercise and recovery, and the findings should be used in future study design.
... Significant group differences with p < 0.05 are given in bold Figure 5 shows the dynamics of the mean (normalized) PCr levels and mean pH values for both muscles and athlete groups during the L 180 phase. Endurance-trained subjects revealed distinctly higher PCr depletion in the SOL (35 (15,45 Figure 5A, right chart). ...
... 33 Overall, the changes in the global parameters seem to be predominantly driven by the distinctly more pronounced metabolic adaptations of the GM muscle, which acts as the main contributor of force generation in our plantar flexion setup. 45 In contrast, the SOL plays a supporting role and affects the global adjustments to a lesser extent than the GM, as also reflected in its distinctly lower metabolic changes. ...
... 46 This, in turn, could affect the preference of either aerobic or anaerobic energy supply in the SOL and GM, respectively. 45,46 Furthermore, the mainly oxidative metabolic contribution is reflected in the present experiment by exercise-induced pH levels around 7.0 in the SOL of athletes with exercise durations greater than 350 s. 34 Other authors confirmed the assumption of different metabolic domains in which the two muscles are working. 32,50 Thus, based on the conclusions drawn from recent findings, the pH and PCr kinetics measured in the present study indicate that the GM is characterized by higher activation and higher acidification as well as a presumably higher impact of glycolytic energy supply compared with the SOL. ...
Article
Measurements of exercise-induced metabolic changes, such as oxygen consumption, carbon dioxide exhalation or lactate concentration, are important indicators for assessing the current performance level of athletes in training science. With exercise-limiting metabolic processes occurring in loaded muscles, ³¹P-MRS represents a particularly powerful modality to identify and analyze corresponding training-induced alterations. Against this background, the current study aimed to analyze metabolic adaptations after an exhaustive exercise in two calf muscles (m. soleus – SOL – and m. gastrocnemius medialis – GM) of sprinters and endurance athletes by using localized dynamic ³¹P-MRS. In addition, the respiratory parameters VO2 and VCO2, as well as blood lactate concentrations, were monitored simultaneously to assess the effects of local metabolic adjustments in the loaded muscles on global physiological parameters. Besides noting obvious differences between the SOL and the GM muscles, we were also able to identify distinct physiological strategies in dealing with the exhaustive exercise by recruiting two athlete groups with opposing metabolic profiles. Endurance athletes tended to use the aerobic pathway in the metabolism of glucose, whereas sprinters produced a significantly higher peak concentration of lactate. These global findings go along with locally measured differences, especially in the main performer GM, with sprinters revealing a higher degree of acidification at the end of exercise (pH 6.29 ± 0.20 vs. 6.57 ± 0.21). Endurance athletes were able to partially recover their PCr stores during the exhaustive exercise and seemed to distribute their metabolic activity more consistently over both investigated muscles. In contrast, sprinters mainly stressed Type II muscle fibers, which corresponds more to their training orientation preferring the glycolytic energy supply pathway. In conclusion, we were able to analyze the relation between specific local metabolic processes in loaded muscles and typical global adaptation parameters, conventionally used to monitor the training status of athletes, in two cohorts with different sports orientations.
... Modified leg-press exercises (combined hip and knee extension), on the other hand, target the vastii, with less activation of the rectus femoris 32,33,42 , but also require contribution from the hamstrings and adductor magnus 32,33,42 , thus comprising a more time effective exercise. Calf raises, when appropriately performed, can also be effective in stimulating the peroneal and tibialis posterior muscles groups 43 , though care needs to be taken in exercise selection for calf raises as knee position can markedly modify the contribution of the gastrocnemius and soleus muscles 44 . Controlling the posture of the arch of the foot appears to be an important factor for optimal activation of the tibialis posterior muscle 44,45 , and this should also be incorporated into exercise. ...
... Calf raises, when appropriately performed, can also be effective in stimulating the peroneal and tibialis posterior muscles groups 43 , though care needs to be taken in exercise selection for calf raises as knee position can markedly modify the contribution of the gastrocnemius and soleus muscles 44 . Controlling the posture of the arch of the foot appears to be an important factor for optimal activation of the tibialis posterior muscle 44,45 , and this should also be incorporated into exercise. Exercises to target the muscles of the hip and lumbar spine should also be considered 34,35,37,46,47 . ...
Article
Objectives: The current study aimed to examine the effectiveness of a resistive vibration exercise countermeasure during prolonged bed-rest in preventing lower-limb muscle atrophy. Methods: 20 male subjects underwent 56-days of bed-rest and were assigned to either an inactive control, or a countermeasure group which performed high-load resistive exercises (including squats, heel raises and toe raises) with whole-body vibration. Magnetic resonance imaging of the lower-limbs was performed at twoweekly intervals. Volume of individual muscles was calculated. Results: Countermeasure exercise reduced atrophy in the triceps surae and the vastii muscles (F>3.0, p<.025). Atrophy of the peroneals, tibialis posterior and toe flexors was less in the countermeasure- subjects, though statistical evidence for this was weak (F≤2.3, p≥.071). Atrophy in the hamstring muscles was similar in both groups (F<1.1, p>.38). The adductor longus, sartiorius and rectus femoris muscles showed little loss of muscle volume during bed-rest (F<1.7, p>.15). Conclusions: The countermeasure exercise programme was effective in reducing atrophy in the extensors of the knee and ankle but not the hamstrings.
... The medial (MG) and lateral gastrocnemius (LG) and soleus are known collectively as the triceps surae and work together to aide human locomotion (12). The triceps surae muscles are responsible for plantar flexion of the foot (1) and acting against the forces of gravity in day to day life (18). ...
... The soleus attaches proximally attachment to the posterior surface of the fibula head and distally to calcaneal tuberosity by way of the Achilles tendon (11). Due to the biarticular nature of the MG and LG, the gastrocnemius can produce greater leverage than the soleus which is monoarticlar in nature (12). Due to the biarticular nature of the gastrocnemius, the contribution of ankle plantar flexion is dependent upon both the knee and ankle joints, whereas the soleus may be targeted independent of knee position. ...
Article
Prior research revealed activation differences between the medial (MG) and lateral (LG) gastrocnemius when performing heel raise exercise with neutral (N), internally-rotated (IR) and externally-rotated (ER) foot positions. Studying underlying biomechanics may help explain activation differences. The purpose was to compare ankle (AN), knee (KN), and hip (HI) contributions (initial joint angles) to attaining each initial foot position, ankle flexion-extension range of motion, ankle mechanical energy expenditure, repetition time, and percent cycle concentric-eccentric transition between N, IR, and ER foot positions. Twenty healthy subjects (11 male, 9 female) with resistance training experience performed twelve repetitions of free-weight (135% body mass) heel raise exercise using N, IR and ER foot positions in a counterbalanced order. Forefeet were elevated .05m onto separate forceplates. Electromagnetic sensors secured along dominant lower limb recorded kinematic data. Dependent variables were averaged across five selected repetitions. No significant differences existed for repetition time (P=.209), percent cycle concentric-eccentric transition (P=.668), ankle mechanical energy expenditure (P=.590), and ankle flexion-extension range of motion (P=.129) between foot positions. Post hoc comparison of a significant joint by foot position interaction (P<.001) demonstrated IR>N>ER for the initial HI and KN angles, whereas for AN, ER>IR and N. Between joints: AN<KN and HI for N and AN<KN<HI for IR. Although it was expected the IR/ER/N positions would induce large start AN angle changes, our results reveal the greatest changes at the HI followed by the KN. Small AN differences may be explained by beginning dorsiflexed (close-packed position). Further research is needed to explain the MG and LG activation differences previously reported.
... Magnetic resonance imaging (MRI) is another noninvasive technique allowing functional investigations of muscles during exercise. This functional application of MRI is based on proton transverse relaxation time (T 2 ) changes measured immediately after exercise which appear to be graded with exercise intensity (Fisher et al. 1990) and correlated to integrated EMG (Adams et al. 1992;Price et al. 2003). This has been used in order to investigate the recruitment pattern in exercising muscles (Akima et al. 2000) and to determine how fatigue (Akima et al. 2002) or aerobic capacity (Reid et al. 2001) could influence these exercise-induced T 2 changes. ...
... MRI actually directly investigates peripheral changes whereas EMG measurements provide information related to the level of central activation and previous studies (Adams et al. 1992;Price et al. 2003) showed that these two techniques are very complementary tools for evaluating muscle activity. However, to the best of our knowledge, no study has used both techniques in order to characterize the pattern of muscle recruitment during a specific sport movement. ...
Article
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Although a number of studies have been devoted to the analysis of the activity pattern of the muscles involved in pedaling in sedentary subjects and/or amateur cyclists, data on professional cyclists are scarce and the issue of inter-individual differences has never been addressed in detail. In the present series of experiments, we performed a non-invasive investigation using functional magnetic resonance imaging and surface electromyography to determine the pattern of activity of lower limb muscles during two different exhausting pedaling exercises in eight French professional cyclists. Each subject performed an incremental exercise during which electromyographic activity of eight lower limb muscles and respiratory variables were recorded. After a 3-h recovery period, transverse relaxation times (T2) were measured before and just after a standardized constant-load maximal exercise in order to quantify exercise-related T2 changes. The global EMG activity illustrated by the root mean square clearly showed a large inter-individual difference during the incremental exercise regardless of the investigated muscle (variation coefficient up to 81%). In addition, for most of the muscles investigated, the constant-load exercise induced T2 increases, which varied noticeably among the subjects. This high level of variation in the recruitment of lower limb muscles in professional cyclists during both incremental and constant-load exercises is surprising given the homogeneity related to maximal oxygen consumption and training volume. The high degree of expertise of these professional cyclists was not linked to the production of a common pattern of pedaling and our results provide an additional evidence that the nervous system has multiple ways of accomplishing a given motor task, as has been suggested previously by neural control theorists and experimentalists.
... Differences in muscle fibre distribution may serve as a possible explanation for this slight decrease in pH, as observed in our study. Several studies have shown that the gastrocnemius muscle, containing a high percentage of type II fibres, is mainly activated during plantar flexion at a knee angle of 0°, whereas the soleus muscle, mainly consisting of type I fibres, is relatively inactive under these conditions (McCreary et al. 1996;Price et al. 2003;Vandenborne et al. 2000). Volleyball players, who are supposed to work mainly under aerobic conditions, show less acidosis in the quadriceps muscle during exhaustive exercise compared to bodybuilders, an observation which was explained by a larger percentage of type I fibres in the muscle tissue of the volleyball players (Schunk et al. 1999). ...
... Volleyball players, who are supposed to work mainly under aerobic conditions, show less acidosis in the quadriceps muscle during exhaustive exercise compared to bodybuilders, an observation which was explained by a larger percentage of type I fibres in the muscle tissue of the volleyball players (Schunk et al. 1999). Type I fibres exhibit predominantly an aerobic metabolism, whereas type II fibres provide high rates of force development and a pronounced glycolytic activity (Price et al. 2003;Schunk et al. 1999). Therefore, we speculate that these heterogeneities reported by different studies during moderate muscle exercise might be caused by different fibre distributions in the muscles studied. ...
Article
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According to the literature the steady-state level of phosphocreatine (PCr) has a linear relationship to the workload during muscle exercise intensities below the lactate threshold, whereas this linearity is impaired during exercise intensities above the lactate threshold. The purpose of this study was to investigate the linearity between PCr kinetics and workload during two bouts of isotonic incremental calf exercise with transitions from moderate- to high-intensity as well as from high- to moderate-intensity work rates. Using a whole-body 1.5 T MR scanner and a self-built exercise bench, we performed serial phosphorus-31 magnetic resonance spectroscopy (31P-MRS) with a time resolution of 30 s in nine healthy male volunteers. Changes in PCr, inorganic phosphate (Pi) and pH were statistically evaluated in comparison to the baseline. The exercise protocol started with a 4.5 W interval of 6 min followed by two bouts of 1.5 W increments. The workload was increased in 2-min intervals up to 9 W during the first bout and up to 7.5 W during the second bout. The second bout was preceded by a 4.5 W interval of 2 min and followed by a 4.5 W interval of 4 min. PCr hydrolysis achieved a steady state during each increment and was highly linear to the work rate (r 2, −0.796; P <0.001). Pi accumulated during each bout, whereas the pH decreased continuously during the first bout and did not exhibit any substantial decrease during the second bout. The metabolite levels and pH were expressed as the median value and the range. Our study confirms that steady-state PCr levels also have a linear relationship to work intensities above the lactate threshold, while pH changes do not have any impact on PCr degradation. The lack of substantial changes in pH during the second exercise bout indicates that prior high-intensity exercise leads to an activation of oxidative phosphorylation.
... Despite the development of mfMRI techniques, few studies have investigated the correlation between mfMRI and EMG variables in involved muscle. Indeed, despite the fact that the combining mfMRI and EMG could provide novel insight into the functioning of the neuromuscular system, only two previous studies have used this approach (1,17). Of those, Adams et al. (1) showed that changes in the mfMRI signal correlate well with integrated EMG (iEMG) activity for both concentric and eccentric contractions in biceps brachii, which is composed of similar fiber types. ...
... As mentioned above, the SOL is a monoarticular muscle that originates along the upper two thirds of the posterior surface of the tibia and fibula, and generally has a higher percentage of Type I fibers than the gastrocnemius muscles (6,11). Price et al. (16,17) reported that T2 values for the SOL did not significantly increase from baseline during nonweight-bearing plantarflexion exercise. This suggests that the SOL could be activated by weight bearing, per se, which is consistent with the changes in T2 and EMG activity found in the present study, where a "weight-bearing-exercise" was employed. ...
Article
The aim of the present study was to clarify the neuromuscular activation patterns among individual triceps surae (TS) muscles during a repetitive plantarflexion using muscle functional magnetic resonance imaging (MRI) (mfMRI) and electromyography (EMG). Six healthy men participated in this study, performing 5 sets of 10 repetitions of a calf-raise exercise bilaterally, unilaterally, and unilaterally with an additional 15% of body-weight load. The transverse relaxation times (T2) in the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles were measured from mfMR images obtained with the subject at rest and immediately after exercise; integrated EMG (iEMG) activity was recorded from the same muscles during exercise using surface electrodes. There was remarkable correspondence between the changes in T2 values and iEMG activity under the three different workloads for individual TS muscles. In addition, changes in T2 value that occurred as a function of increasing exercise loads were linearly correlated with iEMG activity in the MG (r=0.58, P<0.05) and SOL (r=0.63, P<0.01), but not in the LG. These results suggest that 1) mfMRI signals and iEMG activity correlate with workload in individual TS muscles, 2) mfMRI signals are associated with neuromuscular activity reflected in iEMG in the MG and SOL but not in the LG, and 3) these relationships are associated with neuromuscular and metabolic factors during exercise.
... The medial (MG) and lateral gastrocnemius (LG) and soleus are known collectively as the triceps surae and work together to aide human locomotion (12). The triceps surae muscles are responsible for plantar flexion of the foot (1) and acting against the forces of gravity in day to day life (18). ...
... The soleus attaches proximally attachment to the posterior surface of the fibula head and distally to calcaneal tuberosity by way of the Achilles tendon (11). Due to the biarticular nature of the MG and LG, the gastrocnemius can produce greater leverage than the soleus which is monoarticlar in nature (12). Due to the biarticular nature of the gastrocnemius, the contribution of ankle plantar flexion is dependent upon both the knee and ankle joints, whereas the soleus may be targeted independent of knee position. ...
Article
Full-text available
ABSTRACT Prior research revealed activation differences between the medial (MG) and lateral (LG) gastrocnemius when performing heel raise exercise with neutral (N), internally-rotated (IR) and externally-rotated (ER) foot positions. Studying underlying biomechanics may help explain activation differences. The purpose was to compare ankle (AN), knee (KN), and hip (HI) contributions (initial joint angles) to attaining each initial foot position, ankle flexion-extension range of motion, ankle mechanical energy expenditure, repetition time, and percent cycle concentric-eccentric transition between N, IR, and ER foot positions. Twenty healthy subjects (11 male, 9 female) with resistance training experience performed twelve repetitions of free-weight (135% body mass) heel raise exercise using N, IR and ER foot positions in a counterbalanced order. Forefeet were elevated .05m onto separate forceplates. Electromagnetic sensors secured along dominant lower limb recorded kinematic data. Dependent variables were averaged across five selected repetitions. No significant differences existed for repetition time (P=.209), percent cycle concentric-eccentric transition (P=.668), ankle mechanical energy expenditure (P=.590), and ankle flexion-extension range of motion (P=.129) between foot positions. Post hoc comparison of a significant joint by foot position interaction (P<.001) demonstrated IR>N>ER for the initial HI and KN angles, whereas for AN, ER>IR and N. Between joints: ANAN
... Previous studies on exercise induced effects on the muscle have shown that muscular activation leads to an increase of the T2 � and T2 relaxation times [4,10,11], with the possibility of determining patterns of spatial distribution as well as quantifying the intensity of muscle activation [12][13][14]. In consideration of the underlying physiology, it is currently assumed that the increase in T2 relaxation time is caused by an increase of the muscular water content due to osmotically induced increase in extra-and intracellular volume and intracellular acidification by products of metabolism, such as lactate, phosphate and sodium [12,[14][15][16]. ...
... The actual times of the individual running sessions largely corresponded to the targeted times with 02:31,53 ± 00:01,86 for the 2.5 minute running segments, 05:01,09 ± 00:03,61 for the 5 minute running segments and 30:01,82 ± 00:03,61 for the 30 minute running segments, respectively. The total time of interruption of the running sessions was 03:43,02 ± 00:36,03, consisting of the scan time (02:13,94 ± 00: 11,17) and the transitions times between scanner and treadmill (01:03,28 ± 00:23,04) and vice versa (00:42,24 ± 00:07,96). ...
Article
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Objectives Previous studies on T2* and T2 relaxation time of the muscles have shown that exercise leads to an initial increase, presumably representing different intramuscular physiological processes such as increase in intracellular volume or blood oxygenation level dependent effects with a subsequent decrease after cessation of exercise. Their behaviour during prolonged exercise is still unknown but could provide important information for example about the pathophysiology of overuse injuries. The aim of this study was to evaluate the temporal course of T2* and T2 relaxation time in extrinsic foot muscles during prolonged exercise and determine the optimal mapping technique. Methods Ten participants had to run a total of 75 minutes at their individual highest possible running speed, with interleaved MR scans at baseline and after 2.5, 5, 10, 15, 45 and 75 minutes. The examined extrinsic foot muscles were manually segmented, and relaxation time were analysed regarding its respective time course. Results T2* and T2 relaxation time showed an initial increase, followed by a plateau phase between 2.5 and 15 minutes and a subsequent decrease. For the T2* relaxation time, this pattern was also apparent, but less pronounced, with more muscles not reaching significance (p<0.05) when comparing different time points. Conclusions T2* and T2 relaxation time showed a similar course with an initial rapid increase, a plateau phase and a subsequent decrease under prolonged exercise. Moderate but long-term muscular activity appears to have a weaker effect on T2* relaxation time than on T2 relaxation time.
... Furthermore, Akima et al. 38) showed a significant correlation between change in T2 and change in EMG activity during knee extension exercise in legs without (r = 0.731, P < 0.001) and with surgery (r = 0.656, P < 0.01; Fig. 5). In contrast, Price et al. 39) reported that T2 response was related to EMG activity in the medial and lateral gastrocnemius muscles, but not the soleus muscle, during repetitive dynamic plantar flexions with knee joint angles of 90˚, 135˚ and 180˚ (where 180˚ corresponded to full extension). Therefore, in some cases exercise-induced change in T2 is not always related to EMG activity. ...
Article
Muscle functional magnetic resonance imaging (mfMRI) is a powerful tool for the visualization of anatomical and functional properties (e.g. levels and patterns of activation) of human skeletal muscles. Fleckenstein et al.¹⁾ first reported that working muscles exert acute effects on MRI signals in 1988, and since this time a lot of attempts have been made to assess function and metabolism of activated muscles in healthy and diseased individuals. This review focuses on five aspects of mfMRI; 1) The relation between mfMRI and other functional parameters of working muscles; 2) Muscle activation patterns during single- and multi-joint exercises; 3) The effect of resistance training on mfMRI; 4) The effect of disuse on mfMRI; and 5) The assessment of inhomogenous activation within a single muscle by mfMRI. Finally future application and potential contribution of mfMRI are discussed.
... Muscle functional magnetic resonance imaging (MRI) has been used to quantify changes in T2 signal intensity on the basis of hemodynamic, metabolic, and mechanical changes that are directly related to neuromuscular activation of muscle tissue. [20][21][22] The use of T2 MRI allows for a noninvasive assessment of individual muscle activation. To our knowledge, this technique has not been used previously to assess activation patterns of the intrinsic foot muscles. ...
Article
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Context: The intrinsic foot muscles maintain the medial longitudinal arch and aid in force distribution and postural control during gait. Impaired intrinsic foot-muscle function has been linked to various foot conditions. Several rehabilitative exercises have been proposed to improve it; however, literature that identifies which individual muscles are activated during specific intrinsic foot-muscle exercises is lacking. Objective: To describe changes in activation of the intrinsic plantar foot muscles after 4 exercises as measured with T2 magnetic resonance imaging (MRI). Design: Descriptive laboratory study. Setting: Research laboratory. Patients or other participants: Eight healthy National Collegiate Athletic Association Division I collegiate cross-country and track athletes (5 men and 3 women: age = 20 ± 0.93 years, height = 180.98 ± 10.84 cm, mass = 70.91 ± 7.82 kg). Intervention(s): Participants underwent T2 MRI before and after each exercise. They completed 1 set of 40 repetitions of each exercise (short-foot exercise, toes spread out, first-toe extension, second- to fifth-toes extension). Main outcome measure(s): Percentage increases in muscle activation of the abductor hallucis, flexor digitorum brevis, abductor digiti minimi, quadratus plantae, flexor digiti minimi, adductor hallucis oblique, flexor hallucis brevis, and interossei and lumbricals (analyzed together) after each exercise were assessed using T2 MRI. Results: All muscles showed increased activation after all exercises. The mean percentage increase in activation ranged from 16.7% to 34.9% for the short-foot exercise, 17.3% to 35.2% for toes spread out, 13.1% to 18.1% for first-toe extension, and 8.9% to 22.5% for second- to fifth-toes extension. All increases in activation had associated 95% confidence intervals that did not cross zero. Conclusions: Each of the 4 exercises was associated with increased activation in all of the plantar intrinsic foot muscles evaluated. These results may have clinical implications for the prescription of specific exercises to target individual intrinsic foot muscles.
... The volumes of interest (VOI) for the three interleaved MRS protocols were positioned in the gastrocnemius muscle ( Fig. 1), as plantar flexion exercise with a straight knee activates primarily this muscle (15,16). ...
Article
A novel method based on interleaved localized 31P- and 1H MRS is presented, by which lactate accumulation and the accompanying changes in high energy phosphates in human skeletal muscle can be monitored simultaneously during exercise and recovery. Lactate is quantified using a localized double quantum filter suppressing the abundant lipid signals while taking into account orientation dependent signal modulations. Lactate concentration after ischemic exercise directly quantified by DQF 1H spectroscopy was 24 +/- 3 mmol/L cell water, while 22 +/- 3 mmol/L was expected on the basis of 31P MRS acquired simultaneously. Lactate concentration in a sample of porcine meat was estimated to be 40 +/- 7 mmol/L by means of DQF quantitation, versus 39 +/- 5 mmol/L by biochemical methods. Excellent agreement is shown between lactate concentrations measured noninvasively by 1H MRS, measured biochemically ex vivo, and inferred indirectly in vivo from changes in pH, P(i), and PCr as obtained from 31P MRS data.
... As part of this, one aspect that can contribute to bone loss is physical inactivity. Bone loss occurs with stroke [1,2], spinal cord injury [3,4], and prolonged bed-rest [5], all of which involve some form of inactivity or reduced function. In manned space research bone loss has been detected to be a serious problem. ...
Article
To better understand the effects of prolonged bed-rest in women, 24 healthy women aged 25 to 40 years participated in 60-days of strict 6° head-down tilt bed-rest (WISE-2005). Subjects were assigned to either a control group (CON, n=8) which performed no countermeasure, an exercise group (EXE, n=8) undertaking a combination of resistive and endurance training or a nutrition group (NUT, n=8), which received a high protein diet. Using peripheral quantitative computed tomography (pQCT) and dual X-ray absorptiometry (DXA), bone mineral density (BMD) changes at various sites, body-composition and lower-leg and forearm muscle cross-sectional area were measured up to 1-year after bed-rest. Bone loss was greatest at the distal tibia and proximal femur, though losses in trabecular density at the distal radius were also seen. Some of these bone losses remained statistically significant one-year after bed-rest. There was no statistically significant impediment of bone loss by either countermeasure in comparison to the control-group. The exercise countermeasure did, however, reduce muscle cross-sectional area and lean mass loss in the lower-limb and also resulted in a greater loss of fat mass whereas the nutrition countermeasure had no impact on these parameters. The findings suggest that regional differences in bone loss occur in women during prolonged bed-rest with incomplete recovery of this loss one-year after bed-rest. The countermeasures as implemented were not optimal in preventing bone loss during bed-rest and further development is required.
... Studies were classified as providing evidence of criterion-related validity when quantitative ultrasound measurements were compared to magnetic resonance imaging (MRI) or computerised tomography for measuring muscle size (Bemben 2002), or to electromyography (EMG) for measuring muscle activation (Price et al 2003). ...
Article
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Is rehabilitative ultrasound imaging a valid measure of trunk muscle size and activation? Are rehabilitative ultrasound imaging measures sensitive to change? Systematic review of studies of criterion-related validity, construct validity, and sensitivity to change. Participants: People with low back pain and asymptomatic controls. Trunk muscle size and activation measured by rehabilitative ultrasound imaging, MRI and/or EMG. 37 studies were included. 10 studies investigated criterion-related validity and provided evidence that while ultrasound may be a valid measure of trunk muscle size, the validity of ultrasound to quantify muscle activation is context-dependent, depending on the muscle involved, the contraction strategy utilised, and the intensity of muscle contraction. 23 studies provided evidence of construct validity by demonstrating the ability of ultrasound measurement to differentiate individuals in terms of back pain, anthropometry, and postures. Six studies contained a limited amount of information about sensitivity to change. CONCLUSIONS. It is valid to use rehabilitative ultrasound imaging to measure trunk muscle size and activation during most isometric sub-maximal contractions. Ultrasound measures appear sensitive to both positive and negative change.
... To date, research also suggests that heel raises performed in different knee positions influences TS muscle specificity. For instance, Price et al. (32) used electromyography (EMG) in conjunction with magnetic resonance imaging techniques to investigate the TS muscles during dynamic plantar-flexion contractions at 3 KF angles: 0°KF, 45°KF, and 90°KF. These authors reported decreasing GM and GL activities with increasing SOL activity as KF was increased. ...
Article
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Triceps surae and Achilles tendon injuries are frequent in sports medicine, particularly in middle-aged adults. Muscle imbalances and weakness are suggested to be involved in the etiology of these conditions, with heel-raise testing often used to assess and treat triceps surae (TS) injuries. Although heel raises are recommended with the knee straight for gastrocnemius and bent for soleus (SOL), the extent of muscle selectivity in these positions is not clear. This study aimed to determine the influence of knee angle and age on TS muscle activity during heel raises. Forty-eight healthy men and women were recruited from a younger-aged (18-25 years) and middle-aged (35-45 years) population. All the subjects performed unilateral heel raises in 0° and 45° knee flexion (KF). Soleus, gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) surface electromyography signals were processed to compute root-mean-square amplitudes, and data were analyzed using mixed-effects models and stepwise regression. The mean TS activity during heel raises was 23% of maximum voluntary isometric contraction when performed in 0° KF and 21% when in 45°. Amplitudes were significantly different between TS muscles (p < 0.001) and KF angles (p < 0.001), with a significant interaction (p < 0.001). However, the age of the population did not influence the results (p = 0.193). The findings demonstrate that SOL activity was 4% greater when tested in 45° compared with 0° KF and 5% lower in the GM and GL. The results are consistent with the recommended use of heel raises in select knee positions for assessing, training, and rehabilitating the SOL and gastrocnemius muscles; however, the 4-5% documented change in activity might not be enough to significantly influence clinical outcome measures or muscle-specific benefits. Contrary to expectations, TS activity did not distinguish between middle-aged and younger-aged adults, despite the higher injury prevalence in middle age.
... Firstly, the plantar flexion torque measured at the knee flexed position may include the effect of gastrocnemius muscles. The rationale for this procedure was as follows; (1) the exerted force was quite low due to the "force-length" relationship (Maganaris 2001), (2) the efficiency of force transmission was lower due to the greater pennation angle (Kawakami et al. 1998), (3) the activation level was low (Price et al. 2003), for the gastrocnemius muscle at the knee flexed position. At present, this procedure has been adopted in some studies (Kawakami et al. 2000;Maganaris 2001). ...
Article
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Purpose The purpose of the present study was to determine the effect of the short latency stretch reflex on passive and active muscle stiffness in the soleus muscle. Methods Fourteen males participated in this study. Passive muscle stiffness was calculated from passive muscle force and fascicle length during passive lengthening at four different angular velocities (5, 50, 100, and 200 deg s⁻¹). Active muscle stiffness was also calculated according to changes in muscle force and fascicle length during fast lengthening at five different angular velocities (100, 200, 300, 500, and 600 deg s⁻¹) after submaximal isometric contraction (30% of maximal voluntary contraction). During the measurements of passive and active muscle stiffness, the amplitude of the short latency stretch reflex in the soleus muscle was measured. Results Change in passive torque and passive muscle stiffness significantly increased, whereas change in the fascicle length decreased, as angular velocity increased. At 100 and 200 deg s⁻¹ (stretch reflex responses were not observed at 5 and 50 deg s⁻¹), the amplitude of the short latency stretch reflex was highly correlated with passive muscle stiffness. Change in torque and active muscle stiffness were highest at 100 deg s⁻¹ and decreased as angular velocity increased. At all angular velocities under active conditions, the amplitude of the short latency stretch reflex was not correlated with active muscle stiffness. Conclusion These results suggest that the short latency stretch reflex affects passive muscle stiffness in the soleus muscle, but not active muscle stiffness.
... Such ''closed-chain'' resistance exercises, will preferentially load muscles, such as the vastii (over the rectus femoris) and adductor magnus (over adductor longus; Enocson et al. 2005;Richardson et al. 1998;Tesch 1999;Yamashita 1988). Finally, specific exercises for the plantar flexors should be considered as part of any post-disuse rehabilitation programme as these muscles are the most affected amongst the lower-limb muscles by inactivity (see also Price et al. 2003). ...
Article
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Patients with medical, orthopaedic and surgical conditions are often assigned to bed-rest and/or immobilised in orthopaedic devices. Although such conditions lead to muscle atrophy, no studies have yet considered differential atrophy of the lower-limb musculature during inactivity to enable the development of rehabilitative exercise programmes. Bed-rest is a model used to simulate the effects of spaceflight and physical inactivity. Ten male subjects underwent 56-days of bed-rest. Magnetic resonance imaging of the lower-limbs was performed at 2-weekly intervals during bed-rest. Volume of individual muscles of the lower-limb and subsequently, rates of atrophy were calculated. Rates of atrophy differed (F = 7.4, p < 0.0001) between the muscles with the greatest rates of atrophy seen in the medial gastrocnemius, soleus and vastii (p < 0.00000002). The hamstring muscles were also affected (p < 0.00015). Atrophy was less in the ankle dorsiflexors and anteromedial hip muscles (p > 0.081). Differential rates of atrophy were seen in synergistic muscles (e.g. adductor magnus > adductor longus, p = 0.009; medial gastrocnemius > lateral gastrocnemius, p = 0.002; vastii > rectus femoris, p = 0.0002). These results demonstrate that muscle imbalances can occur after extended periods of reduced postural muscle activity, potentially hampering recovery on return to full upright body position. Such deconditioned patients should be prescribed "closed-chain" simulated resistance exercises, which target the lower-limb antigravity extensor muscles which were most affected in bed-rest.
... In line with previous studies 19,27,28 , we recognized significantly increased relaxation times after 2.5 min for all measured muscles ranging from 4.49% for the SOL and 15.48% for the MG or 14.28% for LG. While these three muscles work synergistically, the SOL mainly consists of slow-twitching type I muscle fibers 29 with lower relaxation times 30 and is always activated to counteract gravity 31 , which explains the longest relaxation time at baseline and smallest increase during exercise in our study. ...
Article
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The extrinsic foot muscles are essentially for controlling the movement path but our knowledge of their behavior during prolonged running is still very limited. Therefore, this study analyzed the time-course of muscle activation using T2 mapping during 75 min of running. In this prospective study, 19 recreational active runners completed 75 min of treadmill running at a constant speed. Interleaved T2 mapping sequences were acquired and segmented at timepoints 0, 2.5, 5, 10, 15, 45, and 75 min. ANOVA for repeated measurements followed by a Tukey post hoc test and Pearson correlation between running speed and initial signal increase at 2.5 min were calculated. All muscles showed a significant signal increase between baseline and 2.5 min (e.g. medial gastrocnemius: + 15.48%; p < 0.01). This was followed by a plateau phase till 15 min for all but the extensor digitorum longus muscle and a significant decrease at 45 or 75 min for all muscles (all p < 0.05). Correlation between running speed and signal increase was negative for all muscles and significant for both gastrocnemii (e.g. medial: r = − 0.57, p = 0.0104) and soleus (r = − 0.47, p = 0.0412). The decrease of relaxation times times in the later running phases was less pronounced for faster runners (≥ 10 km/h). T2 relaxation times do not only decrease after cessation of exercise but already during prolonged running. The lesser initial increase and later decrease in faster runners may indicate training induced changes.
... In this study, we demonstrate that measuring perfusion in exercising skeletal muscle using ASL at 7 Tesla is feasible. The postexercise tissue perfusion, as can be seen from Figure 3a, is significantly increased mainly in GAS because plantar flexion is mostly performed by these muscles (30). This is consistent with T 2 *-weighted data and previous 31 P-MRS findings (18,31,32). ...
Article
PurposeThe aim of this study was to develop a measurement protocol for noninvasive simultaneous perfusion quantification and T2*-weighted MRI acquisition in the exercising calf muscle at 7 Tesla.Methods Using a nonmagnetic ergometer and a dedicated in-house built calf coil array, dynamic pulsed arterial spin labeling (PASL) measurements with a temporal resolution of 12 s were performed before, during, and after plantar flexion exercise in 16 healthy volunteers.ResultsPostexercise peak perfusion in gastrocnemius muscle (GAS) was 27 ± 16 ml/100g/min, whereas in soleus (SOL) and tibialis anterior (TA) muscles it remained at baseline levels. T2*-weighted and ASL time courses in GAS showed comparable times to peak of 161 ± 72 s and 167 ± 115 s, respectively. The T2*-weighted signal in the GAS showed a minimum during exercise (88 ± 6 % of the baseline signal) and a peak during the recovery (122 ± 9%), whereas in all other muscles only a signal decrease was observed (minimum 91 ± 6% in SOL; 87 ± 8% in TA).Conclusion We demonstrate the feasibility of dynamic perfusion quantification in skeletal muscle at 7 Tesla using PASL. This may help to better investigate the physiological processes in the skeletal muscle and also in diseases such as diabetes mellitus and peripheral arterial disease. Magn Reson Med, 2014. © 2014 Wiley Periodicals, Inc.
... It also indicates that the oxidative capacity of the recruited muscle fibers was relatively homogenous and/or dispersed in a Gaussian distribution with no distinct differences in oxidative capacity among populations of fibers. The human plantar flexion exercise was performed with the knee slightly flexed (ϳ10°), and therefore the medial and lateral gastrocnemius muscles were primarily recruited with the soleus muscles likely active but to a lesser extent (27). Oxidative capacities have been reported to be ϳ50% different at the extreme ranges of the fiber-type phenotypes within the gastrocnemius and soleus muscles of recreationally active human subjects (8). ...
Article
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Previous studies have suggested the recovery of phosphocreatine (PCr) after exercise is at least second-order in some conditions. Possible explanations for higher-order PCr recovery kinetics include heterogeneity of oxidative capacity among skeletal muscle fibers and ATP production via glycolysis contributing to PCr resynthesis. Ten human subjects (28 +/- 3 yr; mean +/- SE) performed gated plantar flexion exercise bouts consisting of one contraction every 3 s for 90 s (low-intensity) and three contractions every 3 s for 30 s (high-intensity). In a parallel gated study, the sciatic nerve of 15 adult male Sprague-Dawley rats was electrically stimulated at 0.75 Hz for 5.7 min (low intensity) or 5 Hz for 2.1 min (high intensity) to produce isometric contractions of the posterior hindlimb muscles. [(31)P]-MRS was used to measure relative [PCr] changes, and nonnegative least-squares analysis was utilized to resolve the number and magnitude of exponential components of PCr recovery. Following low-intensity exercise, PCr recovered in a monoexponential pattern in humans, but a higher-order pattern was typically observed in rats. Following high-intensity exercise, higher-order PCr recovery kinetics were observed in both humans and rats with an initial fast component (tau < 15 s) resolved in the majority of humans (6/10) and rats (5/8). These findings suggest that heterogeneity of oxidative capacity among skeletal muscle fibers contributes to a higher-order pattern of PCr recovery in rat hindlimb muscles but not in human triceps surae muscles. In addition, the observation of a fast component following high-intensity exercise is consistent with the notion that glycolytic ATP production contributes to PCr resynthesis during the initial stage of recovery.
... The deeper lying SOL is connected to tibia and fibula [7], and slightly differs in function. Hence its activation during plantar flexion is also different from the gastrocnemius muscles, the proportion of recruitment depending, amongst others, on the angle of the knee [8]. Based on the differences of these muscles regarding function and anatomy, PCr and Pi kinetics are also expected to differ [9][10][11][12][13][14]. Acquiring nonlocalized data from a mixture of muscle tissues implies averaging across their respective metabolite concentrations, exchange rates and pH. ...
Article
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This study demonstrates the applicability of semi-LASER localized dynamic (31)P MRS to deeper lying areas of the exercising human soleus muscle (SOL). The effect of accurate localization and high temporal resolution on data specificity is investigated. To achieve high signal-to-noise ratio (SNR) at a temporal resolution of 6 s, a custom-built human calf coil array was used at 7T. The kinetics of phosphocreatine (PCr) and intracellular pH were quantified separately in SOL and gastrocnemius medialis (GM) muscle of nine volunteers, during rest, plantar flexion exercise, and recovery. The average SNR of PCr at rest was [Formula: see text] in SOL ([Formula: see text] in GM). End exercise PCr depletion in SOL ([Formula: see text] %) was far lower than in GM ([Formula: see text] %). The pH in SOL increased rapidly and, in contrast to GM, remained elevated until the end of exercise. (31)P MRS in single-shots every 6 s localized in the deeper-lying SOL enabled quantification of PCr recovery times at low depletions and of fast pH changes, like the initial rise. Both high temporal resolution and accurate spatial localization improve specificity of Pi and, thus, pH quantification by avoiding multiple, and potentially indistinguishable sources for changing the Pi peak shape.
... In this light, it may be significant that the leg is extending during the 0 -180°arc, and that the BF L is, therefore, actively lengthening. Because of the higher efficiency of eccentric contractions (31), it is possible that there was electrical activity of the flexors, but that the metabolic response was not large enough to elicit a significant T 2 change [a similar finding of EMG activity during active lengthening of the tibialis anterior muscle without a corresponding T 2 change was observed by Price et al. (23)]. Another possible reason for the difference between the EMG and MRI data is that the EMG data may have been affected by cross talk. ...
Article
Surface electromyography (EMG) can assess muscle recruitment patterns during cycling, but has limited applicability to studies of deep muscle recruitment and electrically stimulated contractions. We determined whether muscle recruitment timing could be inferred from MRI-measured transverse relaxation time constant (T(2)) changes and a cycle ergometer modified to vary power as a function of pedal angle. Six subjects performed 6 min of single-leg cycling under two conditions (E0°-230° and E90°-230°), which increased the power from 0°-230° and 90-230° of the pedal cycle, respectively. The difference condition produced a virtual power output from 0-180° (V0°-180°). Recruitment was assessed by integrating EMG over the pedal cycle (IEMG) and as the (post-pre) exercise T(2) change (ΔT(2)). For E0°-230°, the mean IEMG for vastus medialis and lateralis (VM/VL; 49.3 ± 3.9 mV·s; mean ± SE) was greater (P < 0.05) than that for E90°-230° (17.9 ± 1.9 mV·s); the corresponding ΔT(2) values were 8.7 ± 1.0 and 1.4 ± 0.5 ms (P < 0.05). For E0°-230° and E90°-230°, the IEMG values for biceps femoris/long head (BF(L)) were 37.7 ± 5.4 and 27.1 ± 5.6 mV·s (P > 0.05); the corresponding ΔT(2) values were 0.9 ± 0.9 and 1.5 ± 0.9 ms (P > 0.05). MRI data indicated activation of the semitendinosus and BF/short head for E0°-230° and E90°-230°. For V0°-180°, ΔT(2) was 7.2 ± 0.9 ms for VM/VL and -0.6 ± 0.6 ms for BF(L); IEMG was 31.5 ± 3.7 mV·s for VM/VL and 10.6 ± 7.0 mV·s for BF(L). MRI and EMG data indicate VM/VL activity from 0 to 180° and selected hamstring activity from 90 to 230°. Combining ΔT(2) measurements with variable loading allows the spatial and temporal patterns of recruitment during cycling to be inferred from MRI data.
... For muscle studies in particular, a prolongation in T2 relaxation time between rest and intensive muscle activity has been reported to be useful for a quantitative evaluation of muscle activity [2]. This technique is referred as muscle functional MRI (mfMRI) and has been used in studies on lower back [4][5][6][7], lower limbs [8,9], upper limbs [10,11], shoulder [12], hip abductors [13] and plantar flexion movements [14]. It allowed the estimation of the activity of all muscles in the considered field of view with a single scan, showing particular advantage for the study of deeper muscles that have usually prohibitive access with other methods. ...
Article
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Muscle functional MRI (mfMRI) is an imaging technique that assess muscles’ activity, exploiting a shift in the T2-relaxation time between resting and active state on muscles. It is accompanied by the use of electromyography (EMG) to have a better understanding of the muscle electrophysiology; however, a technique merging MRI and EMG information has not been defined yet. In this paper, we present an anatomical and quantitative evaluation of the method our group introduced in to quantify its validity in terms of muscle pattern estimation for four subjects during four isometric tasks. Muscle activation pattern are estimated using a resistive network to model the morphology in the MRI. An inverse problem is solved from sEMG data to assess muscle activation. The results have been validated with a comparison with physiological information and with the fitting on the electrodes space. On average, over 90% of the input sEMG information was able to be explained with the estimated muscle patterns. There is a match with anatomical information, even if a strong subjectivity is observed among subjects. With this paper we want to proof the method’s validity showing its potential in diagnostic and rehabilitation fields.
... The results of EMG test are different though. Both in a static [29] and dynamic measurement [30] the gastrocnemius exhibited lower functional potential in the flexed-knee position because of the maximum shortening of its muscle fibres [31]. Moreover, Wahakara et al. measured the potential separately for the medial and lateral head of the gastrocnemius. ...
Article
In many small animals there are distinct differences in fiber-type composition among limb muscles, and these differences typically correspond to marked disparities in the oxidative capacities. However, whether there are similar differences in the oxidative capacity among leg muscles in humans is less clear. The purpose of this study was to compare the rate of phosphocreatine (PCr) recovery, a functional in vivo marker of oxidative capacity, in the lateral and medial gastrocnemius, soleus, and the anterior compartment of the leg (primarily the tibialis anterior) of humans. Subjects performed plantar flexion and dorsiflexion gated exercise protocols consisting of 70 sets of three rapid dynamic contractions (<2.86 s) at 20 s intervals (total: 23.3 min). Starting after the sixth set of contractions, (31)P 2-D CSI (8 x 8 matrix, 14-16 cm FOV, 3 cm slice, TR 2.86 s) were acquired via a linear transmit/receive surface coil using a GE 3T Excite System. The CSI data were zero-filled (32 x 32) and a single FID was produced for each time point in the lateral and medial gastrocnemius, soleus, and anterior compartment. The time constant for PCr recovery was calculated from tau = -Deltat/ln[D/(D + Q)], where Q is the percentage change in PCr due to contraction during the steady-state portion of the protocol, D the additional drop in PCr from rest, and Deltat is the interval between contractions. The tau of PCr recovery was longer (p < 0.05) in the anterior compartment (32 +/- 3 s) than in the lateral (23 +/- 2 s) and medial gastrocnemius muscles (24 +/- 3 s) and the soleus (22 +/- 3 s) muscles. These findings suggest that the oxidative capacity is lower in the anterior compartment than in the triceps surae muscles and is consistent with the notion that fiber-type phenotypes vary among the leg muscles of humans.
Article
To determine the distribution of leg muscle activity during heel raises using magnetic resonance imaging (MRI) with special emphasis on quantifying activity across multiple axial sections and to determine if there are differences among portions of active muscles. Pre- and postexercise (heel raise) T2-weighted time measurements were assessed by using repeated-measures analysis of variance (ANOVA) and t tests. Laboratory and MRI suites. Eight healthy volunteers. Unilateral heel raises every 2 seconds for at least 60 seconds. Percentage changes from T2-weighted magnetic resonance images of the lateral gastrocnemius, medial gastrocnemius, peroneus longus, soleus, and tibialis anterior muscles, across 10 axial sections, exercise bouts, and a pre-exercise condition. The lateral gastrocnemius, medial gastrocnemius, peroneus longus, and soleus had significantly larger changes in T2 time from pre-exercise times than did the tibialis anterior for whole muscles as determined by using repeated-measures ANOVA and post hoc analyses. The medial gastrocnemius had a significantly greater change in T2 time than the lateral gastrocnemius. Proximal axial sections of the lateral gastrocnemius, medial gastrocnemius, and soleus had significantly larger changes in T2 time from pre-exercise than did distal sections. This work reconfirms that multiple muscles contribute to plantarflexor forces and additionally shows an apparent proximal versus subvolume organization of activity within the gastrocnemius, medial gastrocnemius, and soleus but not the peroneus longus. This proximal versus distal organization of muscle activity needs further investigation. There may be clinical implications for therapeutic interventions that require accurate placement of electrodes such as biofeedback.
Article
This chapter describes the biophysical basis of magnetic resonance (MR) imaging of small animals. MR images of small animals can be acquired routinely in reasonable times to portray anatomic features and functional characteristics with spatial resolution nearing true microscopic imaging. The primary properties of tissues that modify the nuclear magnetic resonance (NMR) signal are the density of nuclei, the relaxation times of the nuclear magnetization, the magnetic homogeneity of the environment, and the rate of transport of molecules within the medium. It is suggested that relaxation in tissues is affected by interactions that occur between water protons and protons at or near the surface of macromolecules. Longitudinal proton magnetization can be exchanged between water and neighboring nuclei by direct through-space dipolar couplings, as well as by the so-called chemical exchange of protons. It is found that in the presence of applied magnetic field gradients, Brownian motion causes the net signal from water to attenuate to a degree that depends on the rate of diffusion. The physiological influences on NMR relaxation in the intracellular space are also elaborated.
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The purpose of this study was to investigate the differentiation in muscle tissue characteristics and recruitment between the deep and superficial multifidus muscle by magnetic resonance imaging. The multifidus is a very complex muscle in which a superficial and deep component can be differentiated from an anatomical, biomechanical, histological and neuromotorial point of view. To date, the histological evidence is limited to low back pain patients undergoing surgery and cadavers. The multifidus muscles of 15 healthy subjects were investigated with muscle functional MRI. Images were taken under three different conditions: (1) rest, (2) activity without pain and (3) activity after experimentally induced low back muscle pain. The T2 relaxation time in rest and the shift in T2 relaxation time after activity were compared for the deep and superficial samples of the multifidus. At rest, the T2 relaxation time of the deep portion was significantly higher compared to the superficial portion. Following exercise, there was no significant difference in shift in T2 relaxation time between the deep and superficial portions, and in the pain or in the non-pain condition. In conclusion, this study demonstrates a higher T2 relaxation time in the deep portion, which supports the current assumption that the deep multifidus has a higher percentage of slow twitch fibers compared to the superficial multifidus. No differential recruitment has been found following trunk extension with and without pain induction. For further research, it would be interesting to investigate a clinical LBP population, using this non-invasive muscle functional MRI approach.
Article
INTRODUCTION/ PURPOSE: The widespread occurrence of muscular atrophy during immobilization and its reversal presents an important challenge to rehabilitation medicine. We used 3D-magnetic resonance imaging (MRI) in patients with surgically-stabilized ankle mortise fractures to quantify changes in plantarflexor and dorsiflexor muscle size during immobilization and rehabilitation, as well as to evaluate changes in force generating capacity (specific torque). Twenty-individuals participated in a 10 wk rehabilitation program after 7 wk of immobilization. MRIs were acquired at baseline, 2, and 7 wk of immobilization, and at 5 and 10 wk of rehabilitation. Isometric plantarflexor muscle strength testing was performed at 0, 5, and 10 wk of rehabilitation. Dorsiflexors and plantarflexors atrophied 18.9% and 24.4% respectively, the majority of which occurred during the first 2 wk of immobilization (dorsiflexors: 9.6%; plantarflexors: 14.1%). Likewise, more than 50% of hypertrophy during rehabilitation occurred within the first 5 wk of rehabilitation for both the dorsiflexors (12.9%) and plantarflexors (13.2%), when compared to the total amount of hypertrophy over 10 wk of rehabilitation (dorsiflexors: 17.6%, plantarflexors: 22.5%). There were no significant differences in hypertrophy or atrophy of the dorsiflexor or plantarflexor muscles, despite a rehabilitation emphasis on the plantarflexors. Patients had significantly lower plantarflexor specific torque (torque/CSA) than healthy, control subjects immediately after cast immobilization, which did not return to normal after 10 wk of rehabilitation (P < 0.05). Our investigation of the consequences of limb immobilization on rehabilitation outcomes in patients can be applied directly to optimizing rehabilitation programs. Although muscle hypertrophy occurred early during rehabilitation, plantarflexor muscle function (specific torque) should remain the focus of rehabilitation programs because although CSA recovered quickly, specific torque still lagged behind that of control subjects.
Article
Background: The purpose of this study was to investigate phosphocreatine (PCr) and inorganic phosphate levels as well as pH changes in exercising muscle at a workload of 4.5 W under progressive cuff stenoses, whereby the flow reduction due to cuff compression was quantified by flow-sensitive magnetic resonance imaging. Methods: By using a whole-body 1.5-T magnetic resonance scanner and an exercise bench, serial phosphorus 31 (31P) magnetic resonance spectroscopy with a time resolution of 30 seconds was performed in 10 healthy men. Percentage changes in PCr, inorganic phosphate (Pi), and pH were statistically evaluated in comparison with baseline. The exercise protocol was characterized by a constant workload level of 4.5 W. Ischemic conditions were achieved by a cuff that was placed at the upper leg. Consecutively, increments of 0, 60, 90, 120, and 150 mm Hg were applied. Each increment lasted for 3 minutes. The following rest period was 10 minutes. Results: Blood flow increased significantly immediately after the onset of muscle exercise. No significant changes in blood flow were detected as long as the air pressure of the pneumatic cuff was 60 to 90 mm Hg. Significant reductions in blood flow were observed immediately after inflation of the cuff to 120 and 150 mm Hg. PCr passed into a steady state during the first increment with 0 mm Hg and showed no substantial changes during the increment with 60, 90, and 120 mm Hg. PCr hydrolysis seemed progressive during the 150-mm Hg increment. Pi passed into a plateau level at the onset of exercise and increased significantly at the increment of 150 mm Hg. The pH turned into a steady state with no significant changes during the increments up to 120 mm Hg. At 150 mm Hg, pH decreased progressively. PCr levels at the end of the 150-mm Hg increment correlated significantly and moderately with the reduction in blood flow. Conclusions: Our study shows that the ischemic condition during constant muscle exercise is clearly characterized by PCr and Pi kinetics, as well as by pH changes. The correlation between the degree of blood flow reduction and PCr levels in the exercising muscle groups, which are supplied by the stenosed arteries, is the first essential of using 31P magnetic resonance spectroscopy in the assessment of the effect of arterial stenoses on muscle function in claudicants.
Article
The purpose of this study was to determine if muscle activity of the biceps followed by isometric flexion changes T2 measured in the biceps. It is hypothesized that an increase in T2 will be observed in the biceps but not the triceps after flexion exercise. Ten healthy volunteers were imaged with a one‐channel neck coil while seated in a 0.5T upright open MRI using a 3D‐ Double Echo Steady State (DESS) sequence. Volunteers were imaged while relaxing their arm for 10, 20, and 30 minutes, during an isometric biceps flexion immediately following performance of biceps curls to exhaustion, and again after relaxing for 10 and 20 minutes. Voxel‐wise T2 was calculated by fitting to a DESS signal equation to regions segmented at muscle centers to determine mean T2. During isometric biceps flexion immediately following biceps curls, mean T2 increased (average 33%, P<0.05) in the biceps but not the triceps. By 20 minutes after curls, mean T2 decreased (P<0.05), and was near pre‐activity values. In contrast, there was no change in triceps T2 across any activity or post‐activity time‐points. Intra‐rater repeatability was excellent (ICC 0.90‐0.97). This study demonstrated that measuring T2 in an active muscle is feasible using a DESS sequence in an upright open MRI scanner. This could enable study of muscle function while the muscle is working and weight‐bearing, rather than of the “fatigue” of the muscles after activity. In comparison to electromyography (EMG), MRI also enables study of deep muscles and allows simultaneous assessment of activity and function. This article is protected by copyright. All rights reserved.
Article
Mixed model analysis of muscle functional magnetic resonance imaging (MRI) and electromyography (EMG) changes in lumbar muscles during trunk extension exercise at varying intensities. To gain insight within the relationship between muscle functional MRI and activity of the lumbar back muscles, which is related to exercise intensity. It is known that muscle activity during exercise induces a force-sensitive T2 increase; however, it is not known how sensitive this T2 change is. In addition, the association between MRI and EMG measurement was investigated. Multifidus and erector spinae muscle activity was investigated during a trunk extension exercise at 5 increasing loads (from 40% to 80% of 1 repetition maximum), with both MRI and EMG. Data were analyzed using mixed model analysis. Our results indicate a linear relationship between MRI and exercise intensity; for both muscles an increase of 10% exercise intensity corresponds with an increase of the T2 value with 1.18 (0.89, 1.47) ms. Also for EMG there is a linear relationship with exercise intensity; an increase of 10% exercise intensity corresponds with an increase of 6.98 (5.33, 8.62) microV. Furthermore, a linear association between MRI and EMG is acceptable. For the multifidus, an increase of 1 muV (EMG) corresponds with an increase of 0.168 (0.117, 0.219) ms (MRI). For the erector spinae, an increase of 1 microV corresponds with an increase of 0.078 (0.042, 0.114) ms. Both muscle functional MRI and EMG have specific (dis-) advantages and therefore have to be seen as complementary techniques. Nevertheless, our results support the validity of each method and indicate that MRI and EMG can be used independently to quantify lumbar muscle activity.
Article
To compare the pattern of neck extensor muscle use in participants with chronic mechanical neck pain to that of healthy controls during 2 different extension exercises by use of muscle functional magnetic resonance imaging (mfMRI). Cross-sectional. University laboratory. Data recorded from subjects with chronic mechanical neck pain (n=12; 10 women, 2 men) were compared with previously recorded data from healthy subjects (n=11; 7 men, 4 women). Not applicable. mfMRI measures of shifts in T2 relaxation were made for the multifidus, semispinalis cervicis, semispinalis capitis, and splenius capitis muscles, at C2-3, C5-6, and C7-T1 levels, prior and immediately after 2 different exercises: cervical extension in craniocervical neutral (CCN) and cervical extension in craniocervical extension. T2 shift values (difference between pre- and postexercise T2 relaxation values) for each muscle and exercise condition were used for analysis. While there were observed differences in differential activation of the extensor muscles in participants with mechanical neck pain compared with controls, these differences were only evident for the CCN exercise condition and were only observed for 3 out of the 7 muscle regions of interest during this exercise. Results of this study suggest some alteration in the differential activation of the cervical extensors in patients with mechanical neck pain and indicate that further investigation of this muscle group in mechanical neck pain disorders is warranted.
Article
Measuring exercise-induced muscle activity is essential in sports medicine. Previous studies proposed measuring transverse relaxation time (T(2)) using muscle functional magnetic resonance imaging (mfMRI) to map muscle activity. However, mfMRI uses a spin-echo (SE) sequence that requires several minutes for acquisition. We evaluated the feasibility of T(2) mapping of muscle activity using ultrafast imaging, called fast-acquired mfMRI (fast-mfMRI), to reduce image acquisition time. The current method uses 2 pulse sequences, spin-echo echo-planar imaging (SE-EPI) and true fast imaging with steady precession (TrueFISP). SE-EPI images are used to calculate T(2), and TrueFISP images are used to obtain morphological information. The functional image is produced by subtracting the image of muscle activity obtained using T(2) at rest from that produced after exercise. Final fast-mfMRI images are produced by fusing the functional images with the morphologic images. Ten subjects repeated ankle plantar flexion 200 times. In the fused images, the areas of activated muscle in the fast-mfMRI and SE-EPI images were identical. The geometric location of the fast-mfMRI did not differ between the morphologic and functional images. Morphological and functional information from fast-mfMRI can be applied to the human trunk, which requires limited scan duration. The difference obtained by subtracting T(2) at rest from T(2) after exercise can be used as a functional image of muscle activity.
Article
Muscle functional magnetic resonance imaging (mfMRI) is an innovative technique that offers a noninvasive method to quantify changes in muscle physiology following the performance of exercise. The mfMRI technique is based on signal intensity changes due to increases in the relaxation time of tissue water. In contemporary practice, mfMRI has proven to be an excellent tool for assessing the extent of muscle activation following the performance of a task and for the evaluation of neuromuscular adaptations as a result of therapeutic interventions. This article focuses on the underlying mechanisms and methods of mfMRI, discusses the validity and advantages of the method, and provides an overview of studies in which mfMRI is used to evaluate the effect of exercise and exercise training on muscle activity in both experimental and clinical studies.
Article
Muscle functional magnetic resonance imaging (mfMRI) quantifies exercise-induced alterations in soft-aqueous skeletal muscle as a surrogate measure of muscle activity. Because of its excellent spatiotemporal resolution, mfMRI can be used as a noninvasive evaluation of the function of muscles that are challenging to evaluate, such as the serratus anterior (SA) muscle. The purpose of this preliminary study was to investigate the feasibility of evaluating SA muscle function in individuals with neck pain compared with healthy controls using mfMRI. Muscle functional magnetic resonance imaging scans of the SA muscle were obtained before and immediately after an isometric upper limb exercise in 10 subjects with chronic ipsilateral mechanical neck pain and scapular dysfunction (scan on symptomatic side) and in 10 age- and sex-matched healthy subjects. Scans were recorded at 4 intervertebral levels (T6-7, T7-8, T8-9, and T9-10). Differences in water relaxation values (T2 relaxation) quantified from scans before and after exercise were calculated (T2 shift) as a measure of SA muscle activity at each level and compared between groups. There were significant effects for level (P = .03) and significant group × level interactions (P = .04) but no significant main effect for group (P = .59). Post hoc tests revealed that significant differences in T2 shift values between levels were only evident in the healthy control group. This study demonstrated that despite some inherent challenges associated with imaging the SA muscle, mfMRI appears to have adequate spatiotemporal resolution to effectively evaluate SA muscle activity and function in healthy and clinical populations.
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Quantitative MRI of Vastus Medialis, Vastus Lateralis and Gluteus Medius Muscle Workload after Squat Exercise: Comparison Between Squatting with Hip Adduction and Hip Abduction The aim of the present study was to evaluate the use MRI to quantify the workload of gluteus medius (GM), vastus medialis (VM) and vastus lateralis (VL) muscles in different types of squat exercises. Fourteen female volunteers were evaluated, average age of 22 ± 2 years, sedentary, without clinical symptoms, and without history of previous lower limb injuries. Quantitative MRI was used to analyze VM, VL and GM muscles before and after squat exercise, squat associated with isometric hip adduction and squat associated with isometric hip abduction. Multi echo images were acquired to calculate the transversal relaxation times (T2) before and after exercise. Mixed Effects Model statistical analysis was used to compare images before and after the exercise (ΔT2) to normalize the variability between subjects. Imaging post processing was performed in Matlab software. GM muscle was the least active during the squat associated with isometric hip adduction and VM the least active during the squat associated with isometric hip abduction, while VL was the most active during squat associated with isometric hip adduction. Our data suggests that isometric hip adduction during the squat does not increase the workload of VM, but decreases the GM muscle workload. Squat associated with isometric hip abduction does not increase VL workload.
Article
PURPOSE: The purpose of this study was to investigate the change of triceps surae activation during heel raise test in standing among knee flexion angles(, , , ). METHODS: Twenty healthy individuals performed unilateral plantarflexion in standing with , , , knee flexion. Activity of medial gastrocnemius(MG), lateral gastrocnemius(LG), soleus(Sol) was recorded with surface electromyography(EMG). RESULT: The muscle activations induced the four different positions were compared and results showed that was significant difference MG and LG while the angle increase from to , , but Sol did not show significant differences in every angle. CONCLUSION: This study suggest that knee flexion is required to induce a significant mechanical disadvantage of gastrocnemius.
Article
Imaging is a powerful strategy for the visualization of anatomical and functional information (levels and patterns of activation, perfusion, circulation, and metabolism etc.) in human skeletal muscle. Recent innovations in scientific technology, several new techniques and methods have been developing that visualize the function of muscle regarding recruitment, perfusion, and/or metabolism in exercise. This review is focused on three novel imaging techniques; magnetic resonance imaging, positron emission tomography, and near infrared spectroscopic imaging. These noninvasive imaging techniques provide us crucial information about human muscle function in exercise. The information includes following the assignments; 1) training effects on muscle function, 2) differences in muscle function and metabolism between trained and untrained individuals, and 3) heterogeneity of activation perfusion and metabolism within a single muscle or muscle group. Recent research studies applying these imaging techniques to human muscles are discussed in detail in this review.
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P magnetic resonance spectroscopy (MRS) is widely used for non-invasive investigation of muscle metabolism dynamics. This study aims to extend knowledge on parameters derived from these measurements in detail and comprehensiveness: proton (H⁺) efflux, buffer capacity and the contributions of glycolytic (L) and oxidative (Q) rates to ATP synthesis were calculated from the evolutions of phosphocreatine (PCr) and pH. Data are reported for two muscles in the human calf, for each subject and over a wide range of exercise intensities. 22 subjects performed plantar flexions in a 7T MR-scanner, leading to PCr changes ranging from barely noticeable to almost complete depletion, depending on exercise protocol and muscle studied by localized MRS. Cytosolic buffer capacity was quantified for the first time non-invasively and individually, as was proton efflux evolution in early recovery. Acidification started once PCr depletion reached 60–75%. Initial and end-exercise L correlated with end-exercise levels of PCr and approximately linear with pH. Q calculated directly from PCr and pH derivatives was plausible, requiring fewer assumptions than the commonly used ADP-model. In conclusion, the evolution of parameters describing cellular energy metabolism was measured over a wide range of exercise intensities, revealing a relatively complete picture of muscle metabolism.
Article
Object: To assess post-exercise recovery of human calf muscles using dynamic diffusion tensor imaging (dDTI). Materials and methods: DTI data (6 directions, b = 0 and 400 s/mm(2)) were acquired every 35 s from seven healthy men using a 3T MRI, prior to (4 volumes) and immediately following exercise (13 volumes, ~7.5 min). Exercise consisted of 5-min in-bore repetitive dorsiflexion-eversion foot motion with 0.78 kg resistance. Diffusion tensors calculated at each time point produced maps of mean diffusivity (MD), fractional anisotropy (FA), radial diffusivity (RD), and signal at b = 0 s/mm(2) (S0). Region-of-interest (ROI) analysis was performed on five calf muscles: tibialis anterior (ATIB), extensor digitorum longus (EDL) peroneus longus (PER), soleus (SOL), and lateral gastrocnemius (LG). Results: Active muscles (ATIB, EDL, PER) showed significantly elevated initial MD post-exercise, while predicted inactive muscles (SOL, LG) did not (p < 0.0001). The EDL showed a greater initial increase in MD (1.90 × 10(-4)mm(2)/s) than ATIB (1.03 × 10(-4)mm(2)/s) or PER (8.79 × 10(-5) mm(2)/s) (p = 7.40 × 10(-4)), and remained significantly elevated across more time points than ATIB or PER. Significant increases were observed in post-exercise EDL S0 relative to other muscles across the majority of time points (p < 0.01 to p < 0.001). Conclusions: dDTI can be used to differentiate exercise-induced changes between muscles. These differences are suggested to be related to differences in fiber composition.
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In addition to direct assessment of high energy phosphorus containing metabolite content within tissues, phosphorus magnetic resonance spectroscopy (³¹P-MRS) provides options to measure phospholipid metabolites and cellular pH, as well as the kinetics of chemical reactions of energy metabolism in vivo. Even though the great potential of ³¹P-MR was recognized over 30 years ago, modern MR systems, as well as new, dedicated hardware and measurement techniques provide further opportunities for research of human biochemistry. This paper presents a methodological overview of the ³¹P-MR techniques that can be used for basic, physiological, or clinical research of human skeletal muscle and liver in vivo. Practical issues of ³¹P-MRS experiments and examples of potential applications are also provided. As signal localization is essential for liver ³¹P-MRS and is important for dynamic muscle examinations as well, typical localization strategies for ³¹P-MR are also described.
Chapter
Muscles give us both stability and power for all body movements. However, muscle contractions do more than enable our activities of daily living; they also allow us to exercise, which is associated with beneficial effects on longevity, general health, self-esteem, and mood.1,2 With exercise, however, there is also the possibility of injury. Traumatic insults to muscle in athletes are commonplace. In one study of 2873 adolescents, for example, the rate of injuries requiring medical attention was 40 injuries/100 adolescents/ year, with an even higher rate of injuries resulting in time lost from sports (50 injuries/100 adolescents/year).3 With regular recreational activities in adults, the annual injury rate is approximately 6&, and approximately 62& of all sports injuries reportedly result in time taken off work.4 Elite athletes also may be injured. Indeed, the overall level of injury to professional soccer players is approximately 1000 times higher than in industrial occupations that are typically regarded as high risk (e.g., construction, mining).5 Athletic injuries to muscle have a wide variety of causes, treatments, and prognoses. Given that the cause and severity of injuries may be difficult to determine clinically in some cases, magnetic resonance imaging (MRI) is utilized increasingly in identifying the anatomic location and severity of various pain generators in athletes. In so doing, MRI is increasingly playing a key role in influencing treatment, predicting prognosis, assessing therapeutic response, and detecting potential treatment complications. After reviewing the principal indications for imaging of muscle and commonly used MRI techniques, this chapter reviews normal compartmental anatomy, normal anatomic variations, sportsrelated muscle injuries, and major differential diagnoses.
Article
Purpose: To develop a high temporal resolution imaging method that measures muscle-specific phosphocreatine (PCr) resynthesis time constant (τPCr ) and pH changes in muscles of the lower leg following exercise on a clinical 3T MRI scanner. Methods: We developed a frequency-selective 3D non-Cartesian FLORET sequence to measure PCr with 17-mm nominal isotropic resolution (28 mm actual resolution) and 6-s temporal resolution to capture dynamic metabolic muscle activity. The sequence was designed to additionally collect inorganic phosphate spectra for pH quantification, which were localized using sensitivity profiles of individual coil elements. Nineteen healthy volunteers were scanned while performing a plantar flexion exercise on an in-house developed ergometer. Data were acquired with a dual-tuned multichannel coil array that enabled phosphorus imaging and proton localization for muscle segmentation. Results: After a 90-s plantar flexion exercise at 0.66 Hz with resistance set to 40% of the maximum voluntary contraction, τPCr was estimated at 22.9 ± 8.8 s (mean ± standard deviation) with statistical coefficient of determination r(2) = 0.89 ± 0.05. The corresponding pH values after exercise were in the range of 6.9-7.1 in the gastrocnemius muscle. Conclusion: The developed technique allows measurement of muscle-specific PCr resynthesis kinetics and pH changes following exercise, with a temporal resolution and accuracy comparable to that of single voxel (31) P-MRS sequences. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.
Article
MRI of muscle is becoming an increasingly useful diagnostic tool. Multiple studies have now indicated that increased signal intensity noted on MR images of specific denervated muscles corresponds closely with abnormalities on EMG. Further, there are many newer forms of MRI and applied MR technology, including functional MRI, contrast enhanced spin-echo MRI, and more modern MRS. These techniques are allowing MR to play a growing role in the functional and dynamic evaluation of skeletal muscle pathology and injury, body composition, and cardiac disease. Despite these advances in the use of MRI, there are definite limitations. Clinically available MRI still requires the subject to be relatively motionless. This limits its usefulness as a functional assessment tool. Further, available data confirm that MRI is less sensitive in detecting muscle denervation than needle EMG. The degree of abnormality in complete versus incomplete axonal lesions, and the imaging changes occurring with reinnervation, have not been systematically studied. Presently, electrodiagnostic studies are still necessary to differentiate a complete from an incomplete axonal lesion. Better, less subjective, methods of quantifying MR signal intensity need to be developed. With respect to denervation, longitudinal, serial studies in the same patient over an extended time are needed to better define the usefulness of MRI in terms of sensitivity and specificity in relation to time after nerve injury.
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Effects of gastrocnemius glycogen (Gly) concentration on changes in transverse relaxation time (T2; ms) were studied after 5-min plantar flexion at 25% of maximum voluntary contraction (MVC). Gastrocnemius Gly, phosphorus metabolites, and T2 were measured in seven subjects by using interleaved 13C/31P magnetic resonance spectroscopy (MRS) at 4.7 T and magnetic resonance imaging (MRI; 1.5 T). After baseline MRS/MRI, subjects exercised for 5 min at 25% of MVC and were reexamined (MRS/MRI). Subjects then performed approximately 15 min of single-leg toe raises (50 +/- 2% of MVC), depleting gastrocnemius Gly by 43%. After a 1-h rest (for T2 return to baseline), subjects repeated the 5-min protocol, followed by a final MRI/MRS. After the initial 5-min protocol, T2 values increased by 5.9 +/- 0.8 ms (29.9 +/- 0.4 to 35.8 +/- 0.6 ms), whereas Gly did not change significantly (70.5 +/- 6.8 to 67.6 +/- 7.4 mM). After 15 min of toe raises, gastrocnemius Gly was reduced to 40.4 +/- 5.3 mM (P </= 0. 01), recovering to 45.8 +/- 5.3 mM (P </= 0.05) during a 1-h rest. After the second 5-min bout of plantar flexion (reduced Gly at 25% of MVC), T2 values increased by 5.0 +/- 0.8 ms (30.4 to 35.4 ms), whereas muscle Gly rose to 57.6 +/- 5.3 mM. We conclude that muscle Gly concentration per se does not affect exercise-induced T2 increases in the human gastrocnemius.
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In this study, we examined the changes in H-reflex amplitude so as to determine the spinal level neural modulation that may take place to meet the movement demands. To determine the H-reflex amplitude at various phases of hopping, 'phase-dependent' averaging technique was employed by a computerized data processing system (30 times average at every 10 to 30 ms time bins) during the entire hopping cycle. The subject performed three different types of hopping with the resultant mean height and mechanical power being 26.7, 6.2 and 1.7 cm and 2011, 654 and 285 W for SMALL, LIGHT and MAX hopping, respectively. The H-reflex amplitude changes recorded from the medial gastrocnemius (MG) showed progressive and significant increases over the resting standing control value, i.e. peak H-reflex amplitude increased approximately 3.8, 4.2 and 5.0 times during SMALL, LIGHT, and MAX hopping conditions, respectively. The corresponding changes for the soleus (SOL) were 4.2, 3.1, and 1.6 times, respectively. Cross correlation analyses revealed that the H-reflex amplitude changes preceded the force curves approximate 45, 60, and 70 ms during SMALL, LIGHT and MAX hopping movements. These data suggest that spinal reflexes are not stereotyped motor patterns, but can be specifically modulated for different functional requirements of the muscles.
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Exercise is known to produce changes in the amount and distribution of water in skeletal muscle. Because MR imaging is highly sensitive to changes in water distribution, these changes should be detectable under appropriate imaging conditions. Imaging of the forearms and/or legs was performed in 16 volunteers at 0.35 T, before and after exercise. Exercises included finger flexion and extension, wrist flexion, ankle plantar flexion, and great toe extension. In the case of handgrip exercise, the level of exertion was quantitated. Individual muscles were frequently indistinguishable on preexercise scans. After exercise, active and inactive muscles could be clearly distinguished. For example, in the flexor digitorum profundus, finger flexion resulted in an increase in the image-derived estimate of T1 (T1 postexercise was 1037 +/- 162 msec vs T1 preexercise of 590 +/- 49 msec, p less than .001). T2 also increased (T2 postexercise was 35 +/- 2 msec vs T2 preexercise of 28 +/- 1 msec, p less than .001). Relative spin density also increased (p less than .001). T1, T2, and spin density subsequently decreased with time but were still increased above baseline at 10 min postexercise (p less than .005). Signal changes correlated moderately with the level of exertion (r = .63) and fatigue (r = .45). Vascular occlusion did not prevent intensity changes. Thus, changes in skeletal muscle MR signal intensity occur with exercise and appear to parallel known alterations in water distribution.
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The contractile properties of the triceps surae (medial and lateral gastrocnemii and soleus) have been studied in humans. In comparison with most other human muscles, the triceps complex had a slow twitch (mean contraction and half-relaxation times 112.4 +/- 11.1 and 99.6 +/- 14.4 ms, respectively) and a low tetanus fusion frequency (60 Hz). Stretching the muscle caused both the contraction and half-relaxation times to become longer. With the knee bent, the optimum length for torque development corresponded to almost full dorsiflexion of the ankle. Similar results were obtained with the knee extended. The optimum position of the ankle differed considerably from the position of the joint when the leg was at rest. Although the position of the ankle joint affected electromyographic (EMG) activity recorded during maximal voluntary contraction, there was little change in the EMG-to-M wave ratio.
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Five women and 5 men performed maximal isometric and concentric dorsiflexion actions on an isokinetic dynamometer. The concentric actions were done at 10 present velocities ranging from 0.26 to 5.23 rad.s-1. Electromyographic (EMG) recordings were made from one agonist (tibialis anterior (TAI) and two antagonists (soleus [S], lateral gastrocnemius [LG]). The men produced greater absolute torque than the women, but there was no gender difference in the torque/body mass ratio. The shape of the torque-velocity relation was similar in men and women and approximated, but did not match, that obtained in animal preparations or in human studies using electrical stimulation. Agonist TA activation (integrated EMG/movement time) decreased with increasing velocity over the same range of velocities as torque. Antagonist S, but not LG, activation also decreased. The S/TA activation ratio was greater in men than women. In men the S/TA ratio tended to be greater than the LG/TA ratio, whereas the converse was true for women. These data indicate that velocity influences the relative activation of two antagonists in maximal dorsiflexion muscle actions, and that there is an apparent gender difference in the relative activation of two antagonists.
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To provide more comprehensive information on the extent and pattern of muscle activation during running, we determined lower extremity muscle activation by using exercise-induced contrast shifts in magnetic resonance (MR) images during horizontal and uphill high-intensity (115% of peak oxygen uptake) running to exhaustion (2.0-3.9 min) in 12 young women. The mean percentage of muscle volume activated in the right lower extremity was significantly (P <0.05) greater during uphill (73 +/- 7%) than during horizontal (67 +/- 8%) running. The percentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphill running. During horizontal running, the muscles or groups most activated were the adductors (90 +/- 5%), semitendinosus (86 +/- 13%), gracilis (76 +/- 20%), biceps femoris (76 +/- 12%), and semimembranosus (75 +/- 12%). During uphill running, the muscles most activated were the adductors (83 +/- 8%), biceps femoris (79 +/- 7%), gluteal group (79 +/- 11%), gastrocnemius (76 +/- 15%), and vastus group (75 +/- 13%). Compared with horizontal running, uphill running required considerably greater activation of the vastus group (23%) and soleus (14%) and less activation of the rectus femoris (29%), gracilis (18%), and semitendinosus (17%). We conclude that during high-intensity horizontal and uphill running to exhaustion, lasting 2-3 min, muscles of the lower extremity are not maximally activated, suggesting there is a limit to the extent to which additional muscle mass recruitment can be utilized to meet the demand for force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.
Article
Samples of skeletal muscle were taken from 50 sites in each of 6 previously normal male autopsy subjects aged between 17 and 30 years. The respective percentages of Type I and Type II fibres were calculated and showed that there was a wide variation in fibre type proportions between the 6 samples in almost all the muscles studied. Examination of the mean fibre type proportions of each muscle revealed that predominantly tonic muscles had a high percentage of Type I fibres and predominantly phasic muscles had a high percentage of Type II fibres. Most of the muscles studied were known to fulfil both tonic and phasic functions, however, and showed no striking preponderance of either fibre type.The spatial distribution of the fibre types was examined in order to determine whether this was random or not. The number of “enclosed” fibres observed in the actual samples was compared statistically with the number expected to occur in a hexagonal lattice model, assuming a random distribution. In the great majority of muscles, the distribution of the fibre types was in fact random, though isolated instances of grouping of fibres of uniform type were noted in some distal muscles and more regularly in extensor digitorum brevis.The methods used in the quantitative assessment of the proportions and spatial distribution of the respective fibre types in normal muscle have obvious applications in the study of neuromuscular disease.
Article
An ischemic clamp model of exercise was used to evaluate the potential role of blood flow in mediating changes in the magnetic resonance imaging appearance of skeletal muscle. Proton relaxation times of muscle were serially estimated in 10 healthy subjects (a) before exercise, (b) after exercise in the presence of vascular occlusion (VO1), (c) during vascular reocclusion after 1 minute of reperfusion (VO2), and (d) after reinstitution of continuous flow. T1 and T2 of active muscles were increased during VO1. During VO2, there were additional increases in relaxation times of active muscles. Reinstitution of continuous flow was associated with a continuous decrease in the T2 of exercised muscle. Hence, blood flow was not required for increases in T1 and T2 with exercise. Additional relaxation time increases occurred after a brief period of reperfusion; however, continuous flow was associated with a decrease in T2.
The purpose of this study was to compare the behaviour of electromyographic (EMG) power spectrum statistics, mean power frequency (MPF) and median frequency (MF), across increasing force levels of the soleus (SO), gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) muscles. Surface EMG signals of these three muscles were recorded in 12 men and 10 women during both (1) ramp (single ongoing contractions with the force increasing linearly from 0 to 100% of the maximum voluntary contraction (MVC); and (2) step (steady force levels: 10, 20, 30, 40, 60 and 80% MVC) static (isometric) plantar flexions. Power spectral analysis of these signals was performed on single 256-ms windows at all of the above-mentioned force levels, for both types of contraction. The MF and MPF were calculated from each of the obtained spectra. A less pronounced increase in the MF or MPF was expected for the SO because of its higher type I fibre content. The main results are as follows: (1) similar behaviours were found in the value of MPF and MF across increasing force for the SO and GL muscles, while the GM gave rise to a different behaviour; (2) no difference was found between ramp and step contractions in the behaviour of either MF or MPF across force levels; and (3) different behaviours were observed between the MF and MPF across increasing force levels, for both ramp and step contractions. Our initial expectations were thus not confirmed. It is concluded that the present results support the hypothesis that the EMG power spectrum may be more sensitive to the diameter of the fibres than to the fibre type proportion of the triceps surae muscles. Furthermore, the sensitivity of the power spectrum statistics of a given muscle to the low-pass filter effect of its skin layer was also emphasized.
To investigate the influence of the various knee angles and ankle angular velocities on synergistic muscle activities, the surface electromyograms (EMG) were recorded from the triceps surae muscles, i.e. lateral gastrocnemius (LG), medial gastrocnemius (MG) and soleus (SOL) muscles. Six healthy young men performed ankle plantarflexions at three ankle angular velocities of 6, 30 and 60° · s−1 and three knee angles of 0, 30 and 60° (0° equalling full extension) under constant load (5% and 10% maximal voluntary contraction). At the fully-extended knee angle (0°), peak values of integrated EMG (peak iEMG) during ankle plantarflexions were significantly increased (P < 0.05) in MG and in LG, but significantly decreased (P < 0.05) in SOL with increasing angular velocity. On the other hand, although the patterns of variation of the peak iEMG in each muscle at flexed knee angles (30 and 60°) were very similar to the patterns seen at the fully-extended knee angle, there were no significant differences among angular velocities. During ankle plantarflexions at any of the angular velocities (6, 30 and 60° · s−1) the peak iEMG were significantly increased (P < 0.05) in SOL, but were significantly decreased (P < 0.05) in MG following increases in the knee angles. These results would suggest the possibility of selective recruitment of motor units in humans depending on the angular velocity; however, this behaviour would appear to be weakened by fixing at flexed knee angles which cause an inhibitory influence on gastrocnemius muscles and a facilitative influence on SOL.
Article
Length changes of gastrocnemius muscle belly and tendon at different passive tensions and ranges of motion (ROM) were measured in 31 healthy persons and 15 hemiplegic patients with clinically demonstrated ankle joint plantar flexion (PF) contractures. Preliminary studies were done to obtain accurate determination of gastrocnemius muscle insertion and origin points on x-ray films, to calculate the magnification factor due to x-ray beam divergence and to measure the length changes in muscle belly by the use of a wire hook placed at the muscle-tendon junction. Our results revealed: (1) change in length at different passive tensions is in the muscle belly, not in the tendon, (2) in hemiplegic patients no statistical difference in elongational characteristics of affected gastrocnemius muscle bellies with clinically demonstrated ankle PF contractures and of the contralateral nonaffected muscle bellies, (3) spastic and flaccid gastrocnemius muscle bellies are not statistically different in respect to passive elongations, (4) gastrocnemius muscle bellies of both affected and nonaffected legs of hemiplegic patients were statistically different from the muscle bellies of healthy persons in regard to maximal ROM and maxinum muscle belly length changes, (5) there was approximately .5 mm change in the belly length for each degree of ankle ROM, (6) age is not a factor influencing passive elongation of muscle belly, (7) average muscle belly lengths were consistently shorter in hemiplegic muscles while their tendon lengths did not change. The enumerated findings suggest that the limitation of ankle ROM in spastic hemiplegic legs obtained by the standard clinical measurements technique represents a change in muscle belly rest length without a structural contracture of the muscle fibers.
Article
1. Motor units in the first dorsal interosseus muscle of normal human subjects were recorded by needle electrodes, together with the surface electromyogram (e.m.g.). The wave form contributed by each motor unit to the surface e.m.g. was determined by signal averaging. 2. The peak-to-peak amplitude of the wave form contributed to the surface e.m.g. by a motor unit increased approximately as the square root of the threshold force at which the unit was recruited. The peak-to-peak duration of the wave form was independent of the threshold force. 3. Large and small motor units are uniformly distributed throughout this muscle, and the muscle fibres making up a motor unit may be widely dispersed. 4. The rectified surface e.m.g. was computed as a function of force, based on the sample of motor units recorded. The largest contribution of motor unit recruitment occurs at low force levels, while the contribution of increased firing rate becomes more important at higher force levels. 5. Possible bases for the common experimental observation that the mean rectified surface e.m.g. varies linearly with the force generated by a muscle are discussed. E.m.g. potentials and contractile responses may both sum non-linearly at moderate to high force levels, but in such a way that the rectified surface e.m.g. is still approximately linearly related to the force produced by the muscle.
Article
Torque generated about the ankle joints during maximum isometric contraction of the plantar flexor muscles was measured on a subject 4 months after unilateral excision of the entire triceps surae. Resulting torque output on the operated limb was 327 kg-cm, or 38 per cent of the 871 kg-cm total for the sound limb.
Article
To assess the role of glycogenolysis in mediating exercise-induced increases in muscle water as monitored by changes in muscle proton relaxation times on magnetic resonance imaging (MRI) and cross-sectional area (CSA), five patients with myophosphorylase deficiency (MPD) were compared with seven controls. Absolute and relative work loads were matched during ischemic handgrip and graded cycling, respectively. Relaxation times of active muscle did not increase after handgrip in MPD (T1: 1 +/- 14%, P greater than 0.1; T2: 4 +/- 4%, P greater than 0.1) but did in controls (T1: 59 +/- 30%, P less than 0.005; T2: 26 +/- 9%, P less than 0.005). The volume of exercised muscles, estimated by CSA, increased in both groups after handgrip (controls: 13.8 +/- 3.5%, n = 7, P less than 0.0001; MPD: 7.5 +/- 1.5%, n = 4, P less than 0.005), but the change was greater in controls (P less than 0.02). Ischemic handgrip in controls resulted in a large increase in finger flexor signal intensity (SI) on short tau-inversion recovery images (25 +/- 7%, n = 3; P less than 0.005 compared with preexercise) and a further increase with subsequent reflow (43 +/- 11%, n = 3; P less than 0.001 compared with rest); in MPD, SI did not increase. The ratio of active to inactive muscle SI did not increase from rest to maximal cycle exercise in MPD (0 +/- 20%, n = 2, P greater than 0.1) but did in normals (73 +/- 36%, n = 3; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
Article
The aim of this study was to investigate whether the mean power frequency of the electromyogram of the knee extensors was force and/or muscle fibre-type dependent. Ten female subjects performed a gradually increasing static knee extension (5 seconds duration) using an isokinetic dynamometer. Electromyogram-signals were obtained from the vastus lateralis, vastus medialis and the rectus femoris muscles. The torque signal and the three electromyogram signals were recorded on a tape recorder. From the electromyogram recordings the mean power frequency and the signal amplitude were determined. Muscle biopsies were later obtained from the right vastus lateralis and stained for alkaline and acid mATPase for the determination of fibre-type proportion and areas. Both the mean power frequencies and the signal amplitudes of the three knee extensors were positively torque dependent. Furthermore it was found that the fibre type proportion and the regression coefficient of the torque (%)-mean power frequency relationship were positively correlated. Also a negative correlation existed between the type-1 (%) proportion and the intercept of the individual torque (%)-mean power frequency relationships. In contrast to proposed models of the electromyogram signal no correlation was found between the mean power frequency and the fibre area.
Article
We have made in vivo 1H NMR measurements of the time course of pH and lactate in human skeletal muscle after exercise. Spectra were obtained in a 4.7-T 30-cm bore Bruker Biospec spectrometer with a 2.5-cm diameter single surface coil. pH was determined from the shift of the endogenous carnosine H-C2 peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 mM/kg wet wt. Fitting the data shows that the exponential decay of lactate (-0.094 +/- 0.014 min-1. t1/2 = 10.6 min) is slower than that of pH (-0.147 +/- 0.015 min-1, t1/2 = 4.7 min), n = 7 with two different volunteers. These values are significantly different with P less than 0.0005. Relaxation times of lactate and creatine were also measured for lactate quantitation; creatine T1, 1.23 +/- 12 s, T2, 136.2 +/- 26.4 ms (both in resting human muscle); lactate T1 (in postmortem rabbit muscle), 1.0 +/- 11 s and T2, 80 ms (in postexercise human muscle). At the end of intense exercise, the lactate level reached was 25.3 +/- 4.0 mM and the average pH drop was 1.0 pH unit. We discuss the implications of these measurements in conjunction with existing data on other sources of H+ flux, phosphocreatine resynthesis, H+ transport, and contribution of inorganic phosphate to buffering.
Article
Glycogen metabolism in exercising gastrocnemius muscles was examined by natural abundance 13C nuclear magnetic resonance (NMR) spectroscopy. Five-minute 13C-NMR measurement of muscle glycogen had a reproducibility of +/- 6.5% (+/- 4.8 mM). Experiments were performed on healthy fed male and female subjects. Two protocols were followed. 1) Subjects performed plantar flexion from rest at 15, 20, or 25% of maximum voluntary contraction for up to 9 h. 2) Subjects predepleted gastrocnemius glycogen with heavy exercise and then either performed low-intensity exercise as before or rested. Gastrocnemius glycogen was measured by NMR at rest and after each hour of exercise. In some sessions, both the exercised leg and the nonexercised leg were monitored with 13C-NMR. In protocol 1, blood velocity in the femoral artery was similarly assessed with ultrasonography. During low-intensity exercise from rest (protocol 1) muscle glycogen fell to a new steady-state value after several hours and then remained constant despite continued exercise. Mean blood velocity increased ninefold within 2 min of onset of exercise and remained constant thereafter. After predepletion (protocol 2), muscle glycogen was repleted both during low-intensity exercise and at rest. After 1 h the amount of glycogen repletion was greater when coupled with light exercise [48.5 +/- 2.8 mM after 1 h of exercise, 39.7 +/- 1.1 mM after 1 h of rest (P less than 0.05)]. During subsequent light exercise, glycogen reached a steady-state value similar to that obtained in protocol 1, while in resting, recovery glycogen levels continued to increase (+2.7 mM/h) over a 7-h period.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
Exercise selectively increases the signal intensities (SI) of active muscles in T2-weighted magnetic resonance (MR) images. If these SI increases are graded with exercise intensity, the identification of muscle recruitment patterns may be possible using MR imaging. The purpose of this study was to determine the effect of force generation during exercise on muscle T2 values. Also, we examined the effects of extracellular fluid volume (ECV) expansion on muscle T2 values. Transaxial midcalf images were collected before and after exercise on eight volunteers in a 1.5T GE magnet using a standard spin echo sequence. Exercise consisted of three consecutive bouts of ankle dorsiflexion against graded loads. Three subjects also underwent brief bouts of lower leg venous occlusion (ECV expansion) during and in addition to the exercise protocol. T2 values for the dorsiflexors significantly increased after exercise. Greater mean force produced during exercise caused greater increases in T2 after exercise (T2 = 29.6 +/- 0.9 X Force). Exercise and venous occlusion caused equivalent increases in muscle cross-sectional area. These equivalent increases in ECV were not accompanied by equivalent increases in muscle T2; venous occlusion alone caused less than a 5% increase in T2 while exercise caused a 14% to 25% increase. Consequently, a direct relationship between increases in T2 and in ECV after exercise was not established. Venous occlusion during exercise, however, did significantly augment the increase in T2 and ECV of the anterior compartment muscles. Contrast enhancement among muscles after exercise in T2-weighted MR images is dependent on generated force during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
Article
1. We have investigated the possibility that voluntary muscle lengthening contractions can be performed by selective recruitment of fast-twitch motor units, accompanied by derecruitment of slow-twitch motor units. 2. The behaviour of motor units in soleus, gastrocnemius lateralis and gastrocnemius medialis muscles was studied during (a) controlled isotonic plantar flexion against a constant load (shortening contraction, S), maintained plantar flexion, or dorsal flexion resisting the load and gradually yielding to it (lengthening contraction, L), (b) isometric increasing or decreasing plantar torque accomplished by graded contraction or relaxation of the triceps surae muscles, (c) isometric or isotonic ballistic contractions, and (d) periodic, quasi-sinusoidal isotonic contractions at different velocities. The above tasks were performed under visual control of foot position, without activation of antagonist muscles. The motor units discharging during foot rotation were grouped on the basis of the phase(s) during which they were active as S, S + L and L. The units were also characterized according to both the level of isometric ramp plantar torque at which they were first recruited and the amplitude of their action potential. 3. S units were never active during dorsal flexion; some of them were active during the sustained contraction between plantar and dorsal flexion. Most S + L units were active also during the maintenance phase and were slowly derecruited during lengthening; their behaviour during foot rotations was similar to that during isometric contractions or relaxations. L units were never active during either plantar or maintained flexion, but discharged during lengthening contraction in a given range of rotation velocities; the velocity of lengthening consistently influenced the firing frequency of these units. Such dependence on velocity was not observed in S + L units. 4. A correlation was found between the amplitude of the action potential and the threshold torque of recruitment among all the units. In addition, the amplitudes of both the action potential and the threshold torque were higher in the case of L units than in the case of S and S + L units. Most L units could be voluntarily recruited only in the case of ballistic isometric or isotonic contraction. 5. Occasionally, L units were directly activated by electrical stimulation of motor fibres and their conduction velocity was in the higher range for alpha-axons. In contrast, nerve stimulation could induce a reflex activation of S and S + L units.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
Sports-related muscle pain is frequent in both trained and untrained persons; however, its severity and significance may be difficult to assess clinically. The authors used magnetic resonance (MR) imaging to evaluate acute strains and delayed-onset muscle soreness in sedentary subjects and postmarathon myalgia in trained runners. MR imaging documented the distribution of affected muscles and the absence of focal hematoma, fascial herniation, subsequent fibrosis, and fatty infiltration. Pain associated with strain and that occurring several days after exercise were both associated with prolongation of muscle T1 and T2. In a prospective evaluation of delayed-onset muscle soreness, abnormalities depicted at MR imaging persisted longer than symptoms by up to 3 weeks, indicating that MR imaging is sensitive to tissue alteration that is not apparent clinically. Highly trained marathon runners tended to have relatively mild abnormalities involving the myotendinous junctions.
Article
The relationships between the T1 and T2 relaxation times, tissue water content and extracellular fluid space of two types of skeletal muscle groups were studied in rabbits and rats by means of NMR proton spectroscopy (10 MHz). Although there was no significant difference in the total water content between muscles rich in type I (74.5 +/- .8%; soleus) or type II (75.0 +/- .7%; gastrocnemius) fibers, the respective T1 (521 +/- 25 vs. 486 +/- 16 millisecond; p less than .01) and T2 (39.5 +/- 1.8 vs. 36.5 +/- 1.0 millisecond; p less than .01) relaxation times were consistently prolonged. The longer relaxation times of the soleus as compared with the gastrocnemius muscle were related to a larger extracellular fluid space as measured by (35S) sulfate +34.5%; p less than .01). For this reason, it seems likely selective changes in these spaces will be detectable by NMR proton imaging.
Article
1. Raw or rectified and integrated electromyograms (integrated EMGs) of the leg muscles were recorded during (a) isotonic ramp shortening or lengthening contractions consisting of foot plantar flexions against a constant load, or dorsal flexions accomplished by braking the load and yielding to it, respectively, and (b) isometric increasing or decreasing plantar torques accomplished by graded contractions or relaxations of the triceps muscles. 2. During plantar flexions or increasing torques, the EMG of soleus, gastrocnemius lateralis, medialis, and peroneus increased in parallel. During decreasing torques, motor unit derecruitment took place gradually and simultaneously. The tibialis anterior was silent. During dorsal flexions, one of two characteristic patterns was observed in different subjects: (a) soleus was abruptly derecruited at the beginning of the task, while gastrocnemius lateralis (or medialis) exhibited a large recruitment lasting throughout the lengthening contraction; (b) soleus remained active during the task, showing large motor unit potentials, while the gastrocnemius lateralis recruitment was of a lesser extent than in (a). Peroneus derecruitment was gradual and tibialis anterior activity was absent in both cases. 3. The EMG patterns observed during plantar flexions or in increasing and decreasing torques, and the two patterns observed during shortening or lengthening contractions, were closely reproduced during sinusoidal oscillations of the foot or in isometric contractions and relaxations. 4. When recruitment of the gastrocnemius lateralis was present during dorsal flexion, the slope of its integrated EMG envelope was steeper, the higher the velocity of lengthening contraction. The most rapid and the slowest tasks, however, did not require its activation. Gastrocnemius lateralis integrated EMGs of an amplitude similar to those occurring during lengthening contractions were observed only during ballistic plantar flexions. 5. The two patterns of triceps activation occurring during lengthening contraction could be traced to different mechanical characteristics of the soleus muscles, the gastrocnemius lateralis being activated preferentially in subjects with long soleus half-relaxation times, and the soleus in subjects with short soleus half-relaxation times. 6. The soleus and gastrocnemius lateralis H reflexes were tested during shortening and lengthening contractions.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
1. The Hoffman reflex, or H reflex, was strongly modulated in the human soleus muscle during both walking (4 km/h) and running (8 km/h). It was relatively low at the time of heel contact, increased progressively during the stance phase, and reached its maximum amplitude late in the stance phase. During ankle dorsiflexion the H reflex was absent. 2. During running the peak e.m.g. level of the soleus was on average 2.4 times higher than during walking but the maximum amplitude of the H reflex was never larger than during walking. In fact, the H reflex was on average significantly (P less than 0.05 for one-tailed t test) smaller during running than during walking. Furthermore, the slope of the least-squares line fitted to the relation between the H reflex amplitude and the background e.m.g. was always steeper for the walking data than for the running data. 3. The difference in the H reflex in the two tasks is evidence that the size of the H reflex is not simply a passive consequence of the alpha-motoneurone excitation level, as indicated by the e.m.g., but is also influenced by other central neural mechanisms. We suggest that presynaptic inhibition is the most likely mechanism accounting for the change in the slope. 4. The modulation of the reflexes during walking and running can be interpreted in terms of the idea of automatic gain compensation. The decreased gain during running may be appropriate to reduce saturation of motor output and potential instability of the stretch reflex feed-back loop.
Twelve male subjects were tested to determine the relationship between motor unit (MU) activities and surface electromyogram (EMG) power spectral parameters with contractions increasing linearly from zero to 80% of maximal voluntary contraction (MVC). Intramuscular spike and surface EMG signals recorded simultaneously from biceps brachii were analyzed by means of a computer-aided intramuscular MU spike amplitude-frequency (ISAF) histogram and an EMG frequency power spectral analysis. All measurements were made in triplicate and averaged. Results indicate that there were highly significant increases in surface EMG amplitude (71 +/- 31.3 to 505 +/- 188 microV, p less than 0.01) and mean power frequency (89 +/- 13.3 to 123 +/- 23.5 Hz, p less than 0.01) with increasing force. These changes were accompanied by progressive increases in the firing frequency of MU's initially recruited, and of newly recruited MU's with relatively larger spike amplitudes. The group data in the ISAF histograms revealed significant increases in mean spike amplitude (412 +/- 79 to 972 +/- 117 microV, p less than 0.01) and mean firing frequency (17.8 +/- 5.4 to 24.7 +/- 4.1 Hz, p less than 0.01). These data suggest that surface EMG spectral analysis can provide a sensitive measure of the relative changes in MU activity during increasing force output.
Article
During 6 min exercise on a bicycle ergometer the volume of the leg in normal males increased so as to indicate, after correction for increased regional blood volume, an average trans-capillary fluid loss into the leg muscles of 19, 31, and 45 ml/kg tissue at light (300 kpm/min), moderate (900 kpm/min), and heavy (1200–1500 kpm/min) work load. The total fluid loss into the active muscle mass was calculated to comprise about 1100 ml during heavy work. Since the concomitant decrease of plasma volume was 600 ml, it follows that some 500 ml of fluid must have entered the circulatory system during the work. The study indicated that this compensatory fluid gain was accomplished by absorption of extravascular fluid from inactive tissues and partly caused by osmosis resulting from work induced arterial hyperosmolality (average increase 22 mOsm/kg H2O). Fluid absorption from inactive tissues was studied in experimental animals during exercise and in resting humans during arterial hyperosmolality produced by intravenous hypertonic infusions. The investigations suggested that at least half of the fluid gain to the circulatory system in heavy exercise could be ascribed to the increased arterial osmolality and the remainder to a reflex decrease of capillary pressure.
Article
The present study was designed to determine the relative contribution of the gastrocnemius muscle to isometric plantar flexor torque production at varying knee angles, while investigating the activation of the gastrocnemius muscle at standardised non-optimal lengths. Voluntary plantar flexor torque, supramaximally stimulated twitch torque and myoelectric activity (EMG) from the triceps surae were measured at different knee angles. Surface and intra-muscular EMG were recorded from the soleus muscle and the medial and lateral heads of the gastrocnemius muscle in 10 male subjects. With the ankle angle held constant, knee angle was changed in steps of 30 degrees ranging from 180 degrees (extended) to 60 degrees (extreme flexion), while voluntary torque from a 5-s contraction was determined at 10 different levels of voluntary effort, ranging from 10% of maximal effort to maximal effort. To assess effort, supramaximal twitches were superimposed on all voluntary contractions, and additionally during rest. Maximal plantar flexor torque and resting twitch torque decreased significantly in a sigmoidal fashion with increasing knee flexion to 60% of the maximum torque at 180 degrees knee angle. For similar levels of voluntary effort, the EMG root mean square (RMS) of gastrocnemius was less with increased knee flexion, whereas soleus RMS remained unchanged. From these data, it is concluded that the contribution of gastrocnemius to plantar flexor torque is at least 40% of the total torque in the straight leg position. The decrease of gastrocnemius EMG RMS with decreasing muscle length may be brought about by a decrease in the number of fibres within the EMG electrode recording volume and/or impaired neuromuscular transmission.
Article
In this study the function of leg muscles during stretch-shortening cycles in fast running (6 m.s-1) was investigated. For a single stance phase, kinematics, ground reaction forces, and EMG were recorded. First, rough estimates of muscle force, obtained by shifting the EMG curves +90 ms, were correlated with origin-to-insertion velocity (VOI). Second, active state and internal muscle behavior were estimated by using a muscle model that was applied for soleus and gastrocnemius. High correlations were found between estimates of muscle force and VOI time curves for mono-articular hip, knee, and ankle extensor muscles. The correlation coefficients for biarticular muscles were low. The model results showed that active state of gastrocnemius was high during increase of origin-to-insertion length (LOI), whereas active state of soleus was low during the start of increase of LOI and rose to a plateau at the time lengthening ended and shortening started. It seems that the difference in stimulation between gastrocnemius and soleus is a compromise between minimizing energy dissipation and using the stretch-shortening cycle optimally. Furthermore, it was found that the net plantar flexion moment during running reached a value of 302 Nm, which was 158% and 127% higher than the peak values reached in maximal jump and sprint push-offs, respectively. It was argued that the higher mechanical output in running than in jumping could be ascribed to the utilization of the stretch-shortening cycle in running. The higher values in running compared with sprinting, however, may lie in a difference in muscle stimulation.
Article
Magnetic resonance (MR) imaging studies of exercising leg muscles were performed to compare the changes in MR transverse relaxation times (T2) that result from exercise of the anterior tibialis (AT) and extensor digitorum/hallicus longus (E) in the anterior compartment of the lower leg with those T2 changes in the medial and lateral gastrocnemius (G) in the posterior compartment. Spin-echo MR images were obtained at 1.5 Tesla before and during the first 14 min of recovery from dynamic exercise. In order to normalize the exercise, workloads for each subject were set at 25% of the measured maximum voluntary contraction (MVC) of the anterior and posterior compartments. In separate exercise sessions, a nonmagnetic, pneumatic exercise apparatus was employed for either dorsiflexion or plantarflexion against a fixed constant resistance for two different exercise durations (1 min 45 s or 5 min). Transaxial MR images (TR = 1000 ms, TE = 30, 60, 90, 120 ms, 128 x 256 matrix, 1.5 cm slice) were used to calculate T2 values. Although subjects performed approximately 7-fold more work (P < or = 0.001, dorsiflexion vs plantarflexion) during plantarflexion than during