Triceps Surae Muscle Group Research Articles

Does wearing shoes affect your biomechanical efficiency?

Studies involving minimalist shoes have dramatically increased this past 10 years. While a deeper knowledge of the related modifications has ensued regarding the kinematics, electromyographic, and dynamic patterns, little is known regarding the modifications at the muscle forces and muscle fiber levels. The aim of the present study was to assess at a muscular level the modifications brought up when running barefoot, using 0mm midsole height running shoe, or using classical midsole height running shoes. An EMG-Driven model that combines the kinematics, dynamics, and electromyographic data was used to estimate the Triceps Surae (TS) muscle forces and fiber behavior during running using different footwear conditions. Despite differences at the joint level between barefoot and shod running when looking at ankle joint range of motion, or foot-ground angle at touchdown, the results showed no effect of footwear neither on the maximal muscle forces nor on the relative amount of force produced by each muscle within the TS muscle group when wearing different footwear. On the contrary, different behaviors of muscle fibers were shown with lower amplitudes of fiber lengths for the Gastrocnemii biarticular muscles when running barefoot. This particular results reveal that wearing a shoe, even with a very thin sole, could deeply modify the intricate muscle–tendon mechanics of running.

Synchronous EMG Activity in the Piper Frequency Band Reveals the Corticospinal Demand of Walking Tasks

Evidence indicates that the frequency-domain characteristics of surface electromyogram (EMG) signals are modulated according to the contributing sources of neural drive. Modulation of inter-muscular EMG synchrony within the Piper frequency band (30-60Hz) during movement tasks has been linked to drive from the corticospinal tract. However, it is not known whether EMG synchrony is sufficiently sensitive to detect task-dependent differences in the corticospinal contribution to leg muscle activation during walking. We investigated this question in seventeen healthy older men and women. It was hypothesized that, relative to typical steady state walking, Piper band EMG synchrony of the triceps surae muscle group would be reduced for dual-task walking (because of competition for cortical resources), similar for fast walking (because walking speed is directed by an indirect locomotor pathway rather than by the corticospinal tract), and increased when taking a long step (because voluntary gait pattern modifications are directed by the corticospinal tract). Each of these hypotheses was confirmed. These findings support the use of frequency-domain analysis of EMG in future investigations into the corticospinal contribution to control of healthy and disordered human walking.

Trait emotional intelligence, the Big Five personality traits and isometric maximal voluntary contraction level under stress in athletes

ObjectivesThe purpose of the study was to investigate the effects of trait emotional intelligence (EI) and the Big Five personality traits on athletes’ ability to tolerate stress during isometric maximal voluntary contraction (MVC). MethodsFifty-two elite athletes with a mean age of 21.5 year (17 female) volunteered to participate. The Short Form Big Five Inventory and the Schutte Self-Report Emotional Intelligence Test measured personality and trait EI, respectively. Electromyography (EMG) determined the MVC level of the triceps surae muscle group in the absence and presence of a stressor. The mental stressor was to count downwards, repeatedly subtracting 13 from a starting value of 1000. ResultsAthletes’ MVC values were positively associated with conscientiousness and trait EI regardless of the presence or absence of a mental stressor. Two hierarchical regressions were conducted to determine whether personality traits and trait EI could predict MVC values measured during the absence and presence of mental stressor. Results show that personality traits explain variability in MVC values measured in both the absence and the presence of a mental stressor. Further, trait EI increased the model's ability to predict MVC. Personality traits combined with trait EI had stronger predictive ability for MVC values during exposure to a mental stressor. ConclusionAthletes with higher levels of conscientiousness and trait EI may be able to tolerate more stress without a decrease in performance.

Measuring anisotropic muscle stiffness properties using elastography

Physiological and pathological changes to the anisotropic mechanical properties of skeletal muscle are still largely unknown, with only a few studies quantifying changes in vivo. This study used the noninvasive MR elastography (MRE) technique, in combination with diffusion tensor imaging (DTI), to measure shear modulus anisotropy in the human skeletal muscle in the lower leg. Shear modulus measurements parallel and perpendicular to the fibre direction were made in 10 healthy subjects in the medial gastrocnemius, soleus and tibialis anterior muscles. The results showed significant differences in the medial gastrocnemius (μ‖ = 0.86 ± 0.15 kPa; μ⊥ = 0.66 ± 0.19 kPa, P < 0.001), soleus (μ‖ = 0.83 ± 0.22 kPa; μ⊥ = 0.65 ± 0.13 kPa, P < 0.001) and the tibialis anterior (μ‖ = 0.78 ± 0.24 kPa; μ⊥ = 0.66 ± 0.16 kPa, P = 0.03) muscles, where the shear modulus measured in the direction parallel is greater than that measured in the direction perpendicular to the muscle fibres. No significant differences were measured across muscle groups. This study provides the first direct estimates of the anisotropic shear modulus in the triceps surae muscle group, and shows that the technique may be useful for the probing of mechanical anisotropy changes caused by disease, aging and injury.

Muscle Heating With Megapulse II Shortwave Diathermy and ReBound Diathermy

A new continuous diathermy called ReBound recently has been introduced. Its effectiveness as a heating modality is unknown. To compare the effects of the ReBound diathermy with an established deep-heating diathermy, the Megapulse II pulsed shortwave diathermy, on tissue temperature in the human triceps surae muscle. Crossover study. University research laboratory. Participants included 12 healthy, college-aged volunteers (4 men, 8 women; age = 22.2 ± 2.25 years, calf subcutaneous fat thickness = 7.2 ± 1.9 mm). Each modality treatment was applied to the triceps surae muscle group of each participant for 30 minutes. After 30 minutes, we removed the modality and recorded temperature decay for 20 minutes. We horizontally inserted an implantable thermocouple into the medial triceps surae muscle to measure intramuscular tissue temperature at 3 cm deep. We measured temperature every 5 minutes during the 30-minute treatment and each minute during the 20-minute temperature decay. Tissue temperature at a depth of 3 cm increased more with Megapulse II than with ReBound diathermy over the course of the treatment (F₆,₆₆ = 10.78, P < .001). ReBound diathermy did not produce as much intramuscular heating, leading to a slower heat dissipation rate than the Megapulse II (F₂₀,₂₂₀ = 28.84, P < .001). During a 30-minute treatment, the Megapulse II was more effective than ReBound diathermy at increasing deep, intramuscular tissue temperature of the triceps surae muscle group.

The effect of short‐term exercise training and nitric oxide on the adaptation of femoral vascular conductance at the onset of contraction

We tested the hypothesis that short‐term mild‐ (M) and heavy‐intensity (H) exercise training (ET) would speed the adaptation of femoral vascular conductance (FVC) at the onset of contraction by a nitric oxide (NO) dependent mechanism. Sprague‐Dawley rats (n=18) were randomized to sedentary (S), M (20m/min5% grade) or H (40m/min5% grade) ET groups and trained 5d/wkfor 4 wks with equal ET volume. Rats were anesthetised and instrumented for measurement of arterial blood pressure and femoral artery blood flow. FVC was calculated. The triceps surae muscle group was stimulated to contract at 30% and 60% of maximal contractile force (MCF) before and after NO synthase blockade (L‐NAME, 5mg/kg IV). FVC data were fit with a mono‐exponential model. The time constant (τ) for FVC was not different (p&gt;;0.05) between groups at 30% (S = 18 ± 13s; M = 15 ± 5s; H = 13 ± 14s) or 60% MCF (S = 24 ± 17s; M = 16 ± 4s; H = 19 ± 4s). L‐NAME increased (p&lt;0.05) τ in all groups at 30% MCF (S = 25 ± 12s; M = 21 ± 6s; H = 27 ± 13s), but did not alter (p&gt;;0.05) τ at 60% MCF (S = 25 ± 9s; M = 22 ± 9s; H = 20 ± 3s). The primary findings from this study were that: 1) short‐term ET did not alter the adaptation of FVC at the onset of contraction; and 2) regardless of training status, NO contributed to the regulation of FVC kinetics at the onset of moderate‐intensity contraction (30% MCF), whereas NO was not required for vasodilation at the onset of heavy‐intensity contraction (60% MCF). NSERC, Canada.

Tetrahydrobiopterin attenuates sympathetic vasoconstrictor responsiveness in resting and contracting skeletal muscle

We tested the hypothesis that acute tetrahydrobiopterin (BH4) supplementation would attenuate sympathetic vasoconstrictor responsiveness in resting and contracting skeletal muscle. Sprague‐Dawley rats (n=15) were anesthetised and instrumented for lumbar sympathetic chain stimulation and measurement of arterial blood pressure and femoral artery blood flow. Femoral vascular conductance (FVC) was calculated. The sciatic nerve was stimulated to contract the triceps surae muscle group at 30 and 60% of maximal contractile force (MCF). The percent change in FVC in response to sympathetic stimulation at 2 and 5 Hz was determined at rest and during contraction before and after BH4 (20mg/kg + 10mg/kg/hr IA) supplementation. BH4 blunted (p&lt;0.05) the vascular response to sympathetic stimulation at rest (CONTROL: 2Hz: −28 ± 5%; 5Hz: −45 ± 5%; BH4: 2Hz: −17 ± 4%; 5Hz: −34 ± 7%) and during contraction at 30%MCF (CONTROL: 2Hz: −14 ± 6%; 5Hz: −28 ± 11%; BH4: 2Hz: −6 ± 6%; 5Hz: −16 ± 10%) and 60%MCF (CONTROL: 2Hz: −7 ± 3%; 5Hz: −16 ± 6%; BH4: 2Hz: −3 ± 3%; 5Hz: −11 ± 6%). In conclusion, acute supplementation of the nitric oxide synthase cofactor BH4 reduced the vascular response to sympathetic stimulation in resting and contracting skeletal muscle. These data demonstrate that BH4 supplementation augmented nitric oxide‐mediated inhibition of sympathetic vasoconstriction. NSERC, Canada.

Short‐term exercise training enhances functional sympatholysis through a nitric oxide‐dependent mechanism

We tested the hypothesis that short-term mild- (M) and heavy-intensity (H) exercise training would enhance sympatholysis through a nitric oxide (NO)-dependent mechanism. Sprague-Dawley rats (n = 36) were randomly assigned to sedentary (S) or to M (20 m min(-1) 5% gradient) or H exercise training groups (40 m min(-1) 5% gradient). Rats assigned to M and H groups trained on 5 days week(-1) for 4 weeks, with the volume of training being matched between groups. Rats were anaesthetized and instrumented for stimulation of the lumbar sympathetic chain and the measurement of arterial blood pressure and femoral artery blood flow. The triceps surae muscle group was stimulated to contract rhythmically at 30 and 60% of maximal contractile force (MCF). The percentage change of femoral vascular conductance (%FVC) in response to sympathetic stimulation delivered at 2 and 5 Hz was determined at rest and during contraction at 30 and 60% MCF. The vascular response to sympathetic stimulation was reduced as a function of MCF in all rats (P < 0.05). At 30% MCF, the magnitude of sympatholysis (%FVC rest - contraction; %FVC) was greater in H compared with M and S groups (%FVC at 2 Hz, S, 9 ± 5; M, 11 ± 8; and H, 18 ± 7; and %FVC at 5 Hz, S, 6 ± 6; M, 12 ± 9; and H, 18 ± 7; P < 0.05) and was greater in H and M compared with S at 60% MCF (%FVC at 2 Hz, S, 15 ± 5; M, 25 ± 3; and H, 36 ± 6; and %FVC at 5 Hz, S, 22 ± 6; M, 33 ± 9; and H, 39 ± 9; P < 0.05). Blockade of NO synthase did not alter the magnitude of sympatholysis in S during contraction at 30 or 60% MCF. In contrast, NO synthase inhibition diminished sympatholysis in H at 30% MCF and in M and H at 60% MCF (P < 0.05). The present findings indicate that short-term exercise training augments sympatholysis in a training-intensity-dependent manner and through an NO-dependent mechanism.

Neuromuscular determinants of maximum walking speed in well-functioning older adults

Maximum walking speed may offer an advantage over usual walking speed for clinical assessment of age-related declines in mobility function that are due to neuromuscular impairment. The objective of this study was to determine the extent to which maximum walking speed is affected by neuromuscular function of the lower extremities in older adults. We recruited two groups of healthy, well functioning older adults who differed primarily on maximum walking speed. We hypothesized that individuals with slower maximum walking speed would exhibit reduced lower extremity muscle size and impaired plantarflexion force production and neuromuscular activation during a rapid contraction of the triceps surae muscle group (soleus (SO) and gastrocnemius (MG)).All participants were required to have usual 10-meter walking speed of >1.0m/s. If the difference between usual and maximum 10m walking speed was <0.6m/s, the individual was assigned to the “Slower” group (n=8). If the difference between usual and maximum 10-meter walking speed was >0.6m/s, the individual was assigned to the “Faster” group (n=12). Peak rate of force development (RFD) and rate of neuromuscular activation (rate of EMG rise) of the triceps surae muscle group were assessed during a rapid plantarflexion movement. Muscle cross sectional area of the right triceps surae, quadriceps and hamstrings muscle groups was determined by magnetic resonance imaging.Across participants, the difference between usual and maximal walking speed was predominantly dictated by maximum walking speed (r=.85). We therefore report maximum walking speed (1.76 and 2.17m/s in Slower and Faster, p<.001) rather than the difference between usual and maximal. Plantarflexion RFD was 38% lower (p=.002) in Slower compared to Faster. MG rate of EMG rise was 34% lower (p=.01) in Slower than Faster, but SO rate of EMG rise did not differ between groups (p=.73). Contrary to our hypothesis, muscle CSA was not lower in Slower than Faster for the muscle groups tested, which included triceps surae (p=.44), quadriceps (p=.76) and hamstrings (p=.98). MG rate of EMG rise was positively associated with RFD and maximum 10m walking speed, but not the usual 10m walking speed.These findings support the conclusion that maximum walking speed is limited by impaired neuromuscular force and activation of the triceps surae muscle group. Future research should further evaluate the utility of maximum walking speed for use in clinical assessment to detect and monitor age-related functional decline.

The Functional Role of the Triceps Surae Muscle during Human Locomotion

AimDespite numerous studies addressing the issue, it remains unclear whether the triceps surae muscle group generates forward propulsive force during gait, commonly identified as ‘push-off’. In order to challenge the push-off postulate, one must probe the effect of varying the propulsive force while annulling the effect of the progression velocity. This can be obtained by adding a load to the subject while maintaining the same progression velocity.MethodsTen healthy subjects initiated gait in both unloaded and loaded conditions (about 30% of body weight attached at abdominal level), for two walking velocities, spontaneous and fast. Ground reaction force and EMG activity of soleus and gastrocnemius medialis and lateralis muscles of the stance leg were recorded. Centre of mass velocity and position, centre of pressure position, and disequilibrium torque were calculated.ResultsAt spontaneous velocity, adding the load increased disequilibrium torque and propulsive force. However, load had no effect on the vertical braking force or amplitude of triceps activity. At fast progression velocity, disequilibrium torque, vertical braking force and triceps EMG increased with respect to spontaneous velocity. Still, adding the load did not further increase braking force or EMG.ConclusionsTriceps surae is not responsible for the generation of propulsive force but is merely supporting the body during walking and restraining it from falling. By controlling the disequilibrium torque, however, triceps can affect the propulsive force through the exchange of potential into kinetic energy.

The effects of verbal encouragement and conscientiousness on maximal voluntary contraction of the triceps surae muscle in elite athletes

We investigated the effect of verbal encouragement on maximal voluntary contraction (MVC) level of the triceps surae muscle group. Our secondary focus was to examine whether the effect of verbal encouragement on MVC level varies as a result of conscientiousness. While the participants performed plantar flexion, MVCs of the triceps surae muscle group were measured using rectified and smoothed surface electromyography (rsEMG) during the absence and presence of verbal encouragement. Participants completed questions from the Five Factor Personality Inventory concerning conscientiousness and were divided into high- and low-conscientiousness groups according to a median split. The sample included 30 female and 53 male elite athletes. In the entire cohort, there was no significant difference in MVCs with and without verbal encouragement. When the sample was partitioned by conscientiousness scores, verbal encouragement led to a significant increase in MVC in the low-conscientiousness group, whereas verbal encouragement led to a non-significant decrease in MVC in the high-conscientiousness group. Percentage change in MVC across experimental conditions was significantly different between the groups, with a 9.72% increase during verbal encouragement of the low-conscientiousness group, and a 2.47% decrease during verbal encouragement of the high-conscientiousness group.

A Comparison of the Effects of 6 Weeks of Traditional Resistance Training, Plyometric Training, and Complex Training on Measures of Strength and Anthropometrics

Complex training (CT; alternating between heavy and lighter load resistance exercises with similar movement patterns within an exercise session) is a form of training that may potentially bring about a state of postactivation potentiation, resulting in increased dynamic power (Pmax) and rate of force development during the lighter load exercise. Such a method may be more effective than either modality, independently for developing strength. The purpose of this research was to compare the effects of resistance training (RT), plyometric training (PT), and CT on lower body strength and anthropometrics. Thirty recreationally trained college-aged men were trained using 1 of 3 methods: resistance, plyometric, or complex twice weekly for 6 weeks. The participants were tested pre, mid, and post to assess back squat strength, Romanian dead lift (RDL) strength, standing calf raise (SCR) strength, quadriceps girth, triceps surae girth, body mass, and body fat percentage. Diet was not controlled during this study. Statistical measures revealed a significant increase for squat strength (p = 0.000), RDL strength (p = 0.000), and SCR strength (p = 0.000) for all groups pre to post, with no differences between groups. There was also a main effect for time for girth measures of the quadriceps muscle group (p = 0.001), the triceps surae muscle group (p = 0.001), and body mass (p = 0.001; post hoc revealed no significant difference). There were main effects for time and group × time interactions for fat-free mass % (RT: p = 0.031; PT: p = 0.000). The results suggest that CT mirrors benefits seen with traditional RT or PT. Moreover, CT revealed no decrement in strength and anthropometric values and appears to be a viable training modality.

Function of the triceps surae muscle group in low and high arched feet: An exploratory study

The Achilles tendon has been shown to be comprised of segmental components of tendon arising from the triceps surae muscle group. Motion of the foot joints in low and high arched feet may induce a change in behaviour of the triceps surae muscle group due to altered strain on the tendon.Surface electromyogram of the medial and lateral gastrocnemius and the soleus muscle from 12 subjects (with 6 low arched and 6 high arched feet) (1:1) was recorded whilst walking at a self selected speed along a 10m walkway.The results showed a high variability in muscle activity between groups with patterns emerging within groups. Soleus was more active in 50% of the low arch feet at forefoot loading and there was a crescendo of activity towards heel lift in 58% of all subjects. This observed variability between groups and foot types emphasises the need for further work on individual anatomical variation and foot function to help in the understanding and management of Achilles tendon pathologies and triceps surae dysfunction.

New Models and Insights into Primate Evolutionary Morphology

New Models and Insights into Primate Evolutionary Morphology

Acute and 2 days delayed effects of exhaustive stretch-shortening cycle exercise on barefoot walking and running patterns

This study investigated the acute and 2days delayed influences of exhaustive stretch-shortening cycle exercise (SSC) on barefoot walking and running gait patterns. The SSC exercise was performed on a sledge apparatus, on which the subjects (N=10) repeated until exhaustion intermittent series of 25 bilateral submaximal rebounds. Maximal drop-jumps and submaximal barefoot treadmill walking and running were performed before (PRE) and after (POST) the exhaustive exercise and repeated 48h (D2) later. Electromyographic activity and 3D kinematics of the right lower limb and foot were recorded for 15s at gait initiation (BEG) and at the end (END: at 3min of walk and 5min of run). The exhaustive SSC exercise resulted in 6% reductions in maximal drop jump performance at POST and D2, and affected mostly both gait patterns at D2. The walking pattern presented compensatory neural adjustments within the triceps surae muscle group. This expected pain-induced protective strategy of the soleus muscle was sufficient to preserve the kinematics pattern. The running condition revealed a major knee strategy, which might support the concept of pain protective strategy of knee extensor muscles at the expense of impact cushioning. Regardless the testing session, most parameters showed fatigue-induced changes at gait initiation (BEG), which were opposite to subsequent BEG to END adjustments. This is likely to support anticipatory strategies rather than progressive adjustments during the exercise.

Similarities and Differences of the Soleus and Gastrocnemius H-reflexes during Varied Body Postures, Foot Positions, and Muscle Function: Multifactor Designs for Repeated Measures

BackgroundAlthough the soleus (Sol), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles differ in function, composition, and innervations, it is a common practice is to investigate them as single H-reflex recording. The purpose of this study was to compare H-reflex recordings between these three sections of the triceps surae muscle group of healthy participants while lying and standing during three different ankle positions.MethodsThe Sol, MG and LG muscles' H-reflexes were recorded from ten participants during prone lying and standing with the ankle in neutral, maximum dorsiflexion, and maximum plantarflexion positions. Four traces were averaged for each combination of conditions. Three-way ANOVAs (posture X ankle position X muscle) with planned comparisons were used for statistical comparisons.ResultsAlthough the H-reflex in the three muscle sections differed in latency and amplitude, its dependency on posture and ankle position was similar. The H-reflex amplitudes and maximum H-reflex to M-response (H/M) ratios were significantly 1) lower during standing compared to lying with the ankle in neutral, 2) greater during standing with the ankle in plantarflexion compared to neutral, and 3) less with the ankle in dorsiflexion compared to neutral during lying and standing for all muscles (p ≤ .05).ConclusionVarying demands are required for muscles activated during distinctly different postures and ankle movement tasks.

Microdialysis and Delivery of Iontophoresis-Driven Lidocaine Into the Human Gastrocnemius Muscle

Iontophoresis is used frequently in physical medicine and rehabilitation, but many research techniques do not adequately measure it for depth of medicine delivery. To determine if iontophoresis delivers lidocaine 5 mm under the surface of human skin. Descriptive laboratory study. Therapeutic modalities research laboratory. Eight men and 5 women volunteers (age range = 21± 2.3 years) who had less than 5 mm of adipose tissue in the area we measured participated in the study. We inserted a microdialysis probe 5 mm under the skin of both legs and into the triceps surae muscle groups of 10 participants. Microdialysis was performed for 60 minutes to allow a recovery period for local skin blood flow to return to baseline. We then delivered 2 mL of 1% lidocaine to the treatment leg via iontophoresis at 40 mA/min. Next, microdialysis was performed continuously in both legs during the treatment and for 30 minutes posttreatment to collect the lidocaine samples. After we had gathered the samples, several saline solutions with various amounts of lidocaine (0.005%, 0.025%, 0.05%, and 0.1 %) were prepared in vitro and analyzed. Although we did not intend to do so as a part of the original study, we also performed an identical follow-up study at 3 mm in 3 participants. Both in vitro and in vivo samples were analyzed via reverse-phase high-performance liquid chromatography (RP-HPLC). A protocol for detection and quantification of lidocaine using RP-HPLC was followed. We did not detect any measurable levels or concentrations of lidocaine in the 10 control samples. According to the RP-HPLC analysis, the 10 treatment samples also were negative for the presence of lidocaine. However, when we performed the study at 3 mm, microdialysis detected lidocaine in the 3 participants at this depth in the treatment leg only. Measurable levels of lidocaine were not detected at 5 mm but were found at 3 mm. More studies are needed to determine the efficacy of microdialysis in measuring iontophoresis-delivered compounds.

Distribution patterns of fibre types in the triceps surae muscle group of chimpanzees and orangutans

Different locomotor and postural demands are met partly due to the varying properties and proportions of the muscle fibre types within the skeletal muscles. Such data are therefore important in understanding the subtle relationships between morphology, function and behaviour. The triceps surae muscle group is of particular interest when studying our closest living relatives, the non-human great apes, as they lack a significant external Achilles tendon, crucial to running locomotion in humans and other cursorial species. The aim of this study, therefore, was to determine the proportions of type I (slow) and type II (fast) fibres throughout these muscles in chimpanzees and orangutans using immunohistochemistry. The orangutan had a higher proportion of type I fibres in all muscles compared with the chimpanzees, related to their slower, more controlled movements in their arboreal habitat. The higher proportion of type II fibres in the chimpanzees likely reflects a compromise between their need for controlled mobility when arboreal, and greater speed and power when terrestrial. Overall, the proportion of slow fibres was greater in the soleus muscle compared with the gastrocnemius muscles, and there was some evidence of proximal to distal and medial to lateral variations within some muscles. This study has shown that not only do orangutans and chimpanzees have very different muscle fibre populations that reflect their locomotor repertoires, but it also shows how the proportion of fibre types provides an additional mechanism by which the performance of a muscle can be modulated to suit the needs of a species.

The effect of varying musculotendinous length on the construction of triceps surae length-tension curves

Introduction: Exercise-induced muscle damage (EIMD) occurs after a bout of unaccustomed exercise, which has effects that peak approximately two days post exercise. Uncertainty exists about the mechanisms and the reliability of some measures of EIMD. A change in the active length-tension relationship of a muscle is often used as a determinant of EIMD, but can be difficult to measure in-vivo. The aim of this experiment was to determine if active length–tension curves could be accurately constructed from the triceps surae muscle group, in vivo, using a commercially available isokinetic dynamometer.

Botulinum Neurotoxin Type A Induces Skeletal Muscle Atrophy Without Altering Heat Shock Protein 70 Expression.

Botulinum neurotoxin type A (BoNT/A) is commonly used as a therapeutic treatment for a number of conditions associated with muscle spasticity in humans. BoNT/A creates a partial paralysis in skeletal muscle by inhibiting release of acetylcholine at the neuromuscular junction; effectively creating a chemical denervation. Like mechanical denervation, this results in significant skeletal muscle atrophy. Our prior studies have shown that heat shock protein 70 (Hsp70) is significantly reduced during various models of skeletal muscle atrophy and, if overexpressed, provides protection against atrophy. PURPOSE: To determine the effect of BoNT/A on Hsp70 expression and CSA in skeletal muscle. METHODS: Male, Sprague-Dawley rats were injected with either a control buffer or three units of Botulinum type A in the triceps surae muscle group. Hindlimbs were then stimulated to confirm force deficit in the triceps surae group and animals were allowed to ambulate normally for either 7 or 14 days. Soleus, plantaris, and gastrocnemius muscles were removed, weighed, and rapidly frozen for cross sectional analysis and Hsp70 protein expression. RESULTS: Force deficits of ∼80% confirmed chemical denervation of the triceps surae muscle group. Gastrocnemius, soleus, and plantaris muscle weights were all significantly decreased (∼36%; ∼31%; ∼54%, respectively) 14 days after injection. Similarly, soleus muscle fiber CSA was significantly decreased (∼25%) in injected limbs. Hsp70 protein expression remained unchanged in the plantaris and soleus muscles 7 and 14 days after BoNT/A injection. CONCLUSION: These data suggest that small doses of BoNT/A cause significant muscle atrophy in a short time period. Unlike other reduced-use models of atrophy, BoNT/A does not cause a reduction in Hsp70. Supported by Ipsen Pharmaceuticals, Ltd.