Effect of countermovement on power–force–velocity profile

Purpose

To study the effect of a countermovement on the lower limb force–velocity (F–v) mechanical profile and to experimentally test the influence of F–v mechanical profile on countermovement jump (CMJ) performance, independently from the effect of maximal power output (P _max).

Methods

Fifty-four high-level sprinters and jumpers performed vertical maximal CMJ and squat jump (SJ) against five to eight additional loads ranging from 17 to 87 kg. Vertical ground reaction force data were recorded (1,000 Hz) and used to compute center of mass vertical displacement. For each condition, mean force, velocity, and power output were determined over the entire push-off phase of the best trial, and used to determine individual linear F–v relationships and P _max. From a previously validated biomechanical model, the optimal F–v profile maximizing jumping performance was determined for each subject and used to compute the individual mechanical F–v imbalance (Fv _IMB) as the difference between actual and optimal F–v profiles.

Results

A multiple regression analysis clearly showed (r ² = 0.952, P < 0.001, SEE 0.011 m) that P _max, Fv _IMB and lower limb extension range (h _PO) explained a significant part of the interindividual differences in CMJ performance (P < 0.001) with positive regression coefficients for P _max and h _PO and a negative one for Fv _IMB.

Conclusion

Compared to SJ, F–v relationships were shifted to the right in CMJ, with higher P _max, maximal theoretical force and velocity (+35.8, 20.6 and 13.3 %, respectively). As in SJ, CMJ performance depends on Fv _IMB, independently from the effect of P _max, with the existence of an individual optimal F–v profile (Fv _IMB having an even larger influence in CMJ).     

Effects of isometric training on the knee extensor moment–angle relationship and vastus lateralis muscle architecture

Purpose

To analyse the muscle adaptations induced by two protocols of isometric training performed at different muscle lengths.

Methods

Twenty-eight subjects were divided into three groups: one (K90) performed isometric training of the knee extensors at long muscle lengths (90° of knee flexion) for 8 weeks, and the second group (K50) at short muscle lengths (50°). The subjects of the third group acted as controls. Isokinetic dynamometry was utilized to analyse the net moment–angle relationship and vastus lateralis muscle thickness at three different locations, and pennation angles and fascicle length at 50 % of thigh length were measured at rest with ultrasonography.

Results

Only subjects from K90 group showed significant increases in isokinetic strength (23.5 %, P < 0.001), while K50 group showed no increases in isokinetic strength: (10 %, P > 0.05). There was a shift in the angle of peak torque of the K90 group to longer muscle lengths (+14.6 %, P = 0.002) with greater increases in isokinetic strength, while the K50 angle shifted to shorter muscle lengths (?7.3 %, P = 0.039). Both training groups showed significant increases in muscle thickness, (K90 9–14 % vs. K50 5–9 %) but only K90 significantly increased their pennation angles (11.7 %, P = 0.038). Fascicle lengths remained unchanged.

Conclusions

Isometric training at specific knee angles led to significant shifts of peak torque in the direction of the training muscle lengths. The greater strength gains and the architectural changes with training at long muscle lengths probably come from a combination of different factors, such as the different mechanical stresses placed upon the muscle–tendon complex.     

Influence of initial metabolic rate on the power–duration relationship for all-out exercise

A single 3-min all-out cycling test can be used to estimate the power asymptote (critical power, CP) and the curvature constant (W') of the power-duration relationship for severe-intensity exercise. It was hypothesized that when exercise immediately preceding the 3-min all-out test was performed CP would systematically reduce the W' without affecting the CP. Seven physically active males completed 3-min all-out cycling tests in randomized order immediately preceded by: unloaded cycling (control); 6-min moderate; 6-min heavy; 2-min severe (S2); or 4-min severe (S4) intensity exercise. The CP was estimated from the mean power output over the final 30 s of the test and the W' was estimated as the power-time integral above end-test power. There were no significant differences in the CP between control (279 ± 62), moderate (275 ± 52), heavy (286 ± 66 W), S2 (274 ± 55), or S4 (273 ± 65 W). The W' was significantly lower (P < 0.05) in S2 (11.5 ± 2.5) and S4 (8.9 ± 2.2) than in control (16.3 ± 2.3), moderate (17.2 ± 2.4) and heavy (15.6 ± 2.3 kJ). These results support the notion that the W' is predictably depleted only at a power output >CP whereas the CP is independent of the mechanisms which reduce W'.     

Quadriceps maximal power and optimal shortening velocity in 335 men aged 23–88 years

The ability to develop adequate quadriceps muscle power may be highly predictive of subsequent disability among older persons. Rate as well as quantitative (sarcopenia) and qualitative (among other slowing of muscles) contributors to that age-related power decline are poorly known. The relationship of quadriceps maximal short-term power (P_max) and corresponding optimal shortening velocity (_opt) with age was assessed in 335 healthy men aged 23–88 years. The P_max and _opt were measured on a friction loaded non-isokinetic cycle ergometer. Anthropometric dimensions were used to estimate lean thigh volume (LTVest) and quadriceps mass. The decline in P_max across the adult life span (10.7% per decade) was greater than the usually reported decrease in maximal muscle strength. Power decreased already after the fourth decade. Both muscle mass (4.1% decline for LTVest or 3.4% for quadriceps mass per decade) and _opt (6.6% decline per decade) contributed to the decrease in power. Age contributed to the variability in P_max independently to the LTVest/quadriceps mass and _opt. The age-related decrease pattern of P_max reflects both stabilization (or even increase) of anthropometric measures (LTVest or quadriceps mass) from youth to middleage and systematic decline of _opt already from the thirties. This implicates more focus on velocity-orientated training as a means of enhancing leg power and improving functional status.     

Influence of road incline and body position on power–cadence relationship in endurance cycling

In race cycling, the external power-cadence relationship at the performance level, that is sustainable for the given race distance, plays a key role. The two variables of interest from this relationship are the maximal external power output (P (max)) and the corresponding optimal cadence (C (opt)). Experimental studies and field observations of cyclists have revealed that when cycling uphill is compared to cycling on level ground, the freely chosen cadence is lower and a more upright body position seems to be advantageous. To date, no study has addressed whether P (max) or C (opt) is influenced by road incline or body position. Thus, the main aim of this study was to examine the effect of road incline (0 vs. 7%) and racing position (upright posture vs. dropped posture) on P (max) and C (opt). Eighteen experienced cyclists participated in this study. Experiment I tested the hypothesis that road incline influenced P (max) and C (opt) at the second ventilatory threshold ([Formula: see text] and [Formula: see text]). Experiment II tested the hypothesis that the racing position influenced [Formula: see text], but not [Formula: see text]. The results of experiment I showed that [Formula: see text] and [Formula: see text] were significantly lower when cycling uphill compared to cycling on level ground (P < 0.01). Experiment II revealed that [Formula: see text] was significantly greater for the upright posture than for the dropped posture (P < 0.01) and that the racing position did not affect [Formula: see text]. The main conclusions of this study were that when cycling uphill, it is reasonable to choose (1) a lower cadence and (2) a more upright body position.     

Modeling of skeletal muscle: the influence of tendon and aponeuroses compliance on the force–length relationship

The aim of this study was to investigate the influence of changing elastic properties of tendon and aponeuroses on force production and muscle geometry. A three-dimensional, structural, continuum mechanics model of the cat medial gastrocnemius was used for this purpose. Increasing compliance in tendon and aponeuroses caused a decrease in the peak isometric force and a shift of the force–length relationship to the right of the length axis (i.e. toward greater muscle lengths). This result can be explained with the stability condition of the force–length relationship which produced a history dependence of force production that is conceptually in agreement with experimental observations.     

The force–velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions

In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force–velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. Seven subjects performed submaximal voluntary lengthening, shortening(at angular, velocities of +5, –5, +15, –15 and +30, and –30° s^–1) and isometric plantar flexor efforts against an ankle torque motor. Angle-specific (90°) measures of plantar flexor torque plus surface and intramuscular electromyography from soleus, medial gastrocnemius and tibialis anterior were made. The level of activation (30% of maximal voluntary isometric effort) was maintained by providing direct visual feedback of the soleus electromyogram to the subject. In an attempt to isolate the contribution of soleus to the resultant plantar flexion torque, activation of the synergist and antagonist muscles were minimised by: (1) flexing the knee of the test limb, thereby minimising the activation of gastrocnemius, and (2) applying an anaesthetic block to the common peroneal nerve to eliminate activation of the primary antagonist muscle, tibialis anterior and the synergist muscles, peroneus longus and peroneus brevis. Plantar flexion torque decreased significantly (P<0.05) after blocking the common peroneal nerve which was likely due to abolishing activation of the peroneal muscles which are synergists for plantar flexion. When normalised to the corresponding isometric value, the force–velocity relationship between pre- and post-block conditions was not different. In both conditions, plantar flexion torques during shortening actions were significantly less than the isometric torque and decreased at faster velocities. During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).     

Force–velocity and unloaded shortening velocity during graded potassium contractures in frog skeletal muscle fibres

Steady-state conditions of contraction, at maximal and submaximal forces, were produced in intact single muscle fibres, from Rana esculenta, using full tetani and graded K⁺-contractures. The uniformity in radial direction, of spreading of activation produced in K⁺-contractures, was checked in relation to the fibre diameters. The absolute isometric force was similar in tetani and maximal contractures, for fibres with diameters between 40 and 60 m, but not for fibres with diameters greater than about 70 m in which contracture force never reached tetanic force. The force–[K⁺]_o relation was similar for fibres with diameters between 40 and 60 m, but it was right shifted and it had a minor slope for fibres with diameters greater than 65–70 m. This suggests that only in the small diameter fibres (40–60 m) the activation does not fail to penetrate uniformly from the surface towards the fibre core. For fibres selected in the diameter range between 40 and 60 m, force–velocity relations and unloaded shortening velocities were determined in tetani and maximal and submaximal contractures. Data were obtained across a force range of 0.3 to 1 P ₀ (tetanic plateau force). Controlled velocity method was used to obtain force–velocity relations, and slack test to determine the unloaded shortening velocity (V _U). The values of the parameters characterising the force–velocity relation (V ₀ and a/P ₀) and V _U as determined by the slack test did not differ significantly in tetani and contractures, independent of the activation level or absolute force developed by the fibre. These results show that, at least within the range of forces tested, crossbridge kinetics is independent of the number of cycling crossbridges, in agreement with the prediction of the recruitment model of myofilament activation.     

Influence of weight etiology information and trainee characteristics on Physician-trainees’ clinical and interpersonal communication

Objective: This analysis explores the effects of relaying information about the genetic and behavioral causes of obesity (vs. control) on physician trainees’ verbal communication behavior with a virtual patient with obesity. Moderation by physician trainees’ gender and BMI was also assessed.Methods: 119 physician trainees’ verbal responses were recorded and coded using a close-ended content analytic approach.Results: Physician trainees in the behavioral and genetic information conditions were more likely to discuss weight (behavioral: AOR = 5.40; genetic: AOR = 6.58,) and provide lifestyle counseling (behavioral: AOR = 10.92; genetic: AOR = 3.50). Those in the behavioral condition were more likely to make assumptions about the patient’s lifestyle behavior (AOR = 5.53) and use stigmatizing language (AOR = 4.69). Heavier physician trainees in the genetic condition had shorter interactions (β = −0.53, p < 0.01).Conclusion: Emphasizing the genetic causes of overweight offers a potential avenue for encouraging clinical communication with patients with obesity, without also increasing prejudice and bias. Additional efforts may be needed to reap the benefits of genetic information for providers with higher weight.Practice Implications: For providers, considering genetic factors underlying patient body weight and obesity risk may serve to reduce stigmatizing communication with patients.     

Effects of 17 days bedrest on the maximal voluntary isometric torque and neuromuscular activation of the plantar and dorsal flexors of the ankle

Maximal voluntary isometric torque values of the ankle plantar (T _im,_PF) and dorsal flexors (T _im,_DF) were assessed in eight healthy adult males at 5° and 15° of dorsal flexion (DF) and at 5°, 15° and 25° of plantar flexion (PF) with the knee at right angles, before (two times), during (three times) and after (three times) 17 days of 6° head-down tilt bedrest (BR). Integrated electromyograms (iEMG) were also recorded from the gastrocnemius medialis and tibialis anterior. T _im,_PF and the iEMG of the gastrocnemius medialis were significantly larger (by 14% and by 27%, respectively) at the end of recovery than before BR. This was probably the consequence of training and/or habituation leading to: (1) increased activation of the plantar flexors; and (2) decreased co-activation of the antagonist muscles. Neither T _im,_DF nor the tibialis anterior iEMG changed significantly. The effects of BR on muscle performance were evaluated as follows. The net torque generated by a given muscle group was assumed to be the algebraic sum of the torque generated by the agonists and by the antagonists. Thus, for the plantar flexors T_im,PF=αiEMG_Gm − βiEMG_Ta, where: (1) iEMG_Gm and iEMG_Ta are the iEMGs of gastrocnemius medialis and of tibialis anterior during maximal PF; and (2) the constants α and β represent the electromechanical coupling of the plantar (α) and dorsal (β) flexors. Similarly for the dorsal flexors: T_im,DF=βiEMG_Ta − αiEMG_Gm, where iEMG_Ta and iEMG_Gm are the iEMGs of tibialis anterior and gastrocnemius medialis during maximal DF. Torque and iEMG values were assessed for all subjects under all experimental conditions. Thus, since the biomechanical leverage of the system was constant, α and β could be calculated. During BR, α decreased by 25% and it dropped by a further 30% during recovery. In contrast, β remained almost unchanged. This suggests that, in spite of training and/or habituation, BR significantly impaired the maximal isometric performance of the plantar flexors, an effect that continued during the initial 10 days of recovery. Accepted: 4 February 2000     

Influence of simulated microgravity on mechanical properties in the human triceps surae muscle in vivo. I: Effect of 120 days of bed-rest without physical training on human muscle musculo-tendinous stiffness and contractile properties in young women

Purpose

The aim of this study was to investigate the effect of a 120-day 5° head-down tilt (HDT) bed-rest on the mechanical properties of the human triceps surae muscle in healthy young women subjects.

Methods

Measurements included examination of the properties of maximal voluntary contractions (MVC), twitch contractions (P _t) and tetanic contractions (P _o). The difference between P _o and MVC expressed as a percentage of P _o and referred to as force deficiency (P _d), was calculated. Electromyographic (EMG) activity in the soleus muscle, electromechanical delay (EMD) and total reaction time (TRT) were also calculated. EMD was the time interval between the change in EMG and the onset of muscle tension. Premotor time (PMT) was taken to be the time interval from the delivery of the signal to change in EMG.

Results

After HDT P _t, MVC and P _o had decreased by 11.5, 36.1, 24.4 %, respectively, P _d had increased by 38.8 %. Time-to-peak tension had increased by 13.6 %, but half-relaxation time had decreased by 19.2 %. The rate of rise in isometric voluntary tension development had reduced, but no changes were observed in the electrically evoked contraction. EMD had increased by 27.4 %; PMT and TRT decreased by 21.4, and 13.7 %, respectively.

Conclusion

The experimental findings indicated that neural as well as muscle adaptation occurred in response to HDT. EMD is a simple and quick method for evaluation of muscle stiffness changes and can serve as an indicator of the functional condition of the neuromuscular system.     

Electrospun hyaluronate–collagen nanofibrous matrix and the effects of varying the concentration of hyaluronate on the characteristics of foreskin fibroblast cells

In this study we propose a novel electrospinning fabrication process for the production of a nanofibrous matrix composed of collagen and hyaluronate. This procedure utilized 1,1,1,3,3,3-hexafluoro-2-propanol and formic acid as a mixed solvent. Fluorescence microscopy photographs revealed that the resulting electrospun nanofibers contained both collagen and hyaluronate. The mean diameter of the composite nanofibrous matrix (as observed using scanning electron micrographs) was approximately 200 nm; this dimension is similar to that of native fibrous protein within the extracellular matrix. The expression of proteinases (e.g. matrix metalloproteinases, MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have been implicated in epidermal repair during wound healing. Moreover, the characteristics of scarless wounds are known to be related to a decreased ratio of TIMP to MMP expression. In the present study the ratio of expression of TIMP1 to MMP1 was lower in foreskin fibroblast cells that were cultured on a hyaluronate–collagen composite nanofibrous matrix than in those cultured on an exclusively collagen nanofibrous matrix. This indicates that the hyaluronate–collagen composite nanofibrous matrix could potentially be used as a wound dressing for the regeneration of scarless skin.     

Effects of S-glutathionylation on the passive force–length relationship in skeletal muscle fibres of rats and humans

Journal of Muscle Research and Cell Motility - This study investigated the effect of S-glutathionylation on passive force in skeletal muscle fibres, to determine whether activity-related redox...     

Effect of 5 weeks horizontal bed rest on human muscle thickness and architecture of weight bearing and non-weight bearing muscles

The aim of the present study was to investigate the changes in thickness, fascicle length (L (f)) and pennation angle (theta) of the antigravity gastrocnemius medialis (GM) and vastus lateralis (VL) muscles, and the non-antigravity tibialis anterior (TA) and biceps brachii (BB) muscles measured by ultrasonography in ten healthy males (aged 22.3 +/- 2.2 years) in response to 5 weeks of horizontal bed rest (BR). After BR, muscle thickness decreased by 12.2 +/- 8.8% (P < 0.05) and 8.0 +/- 9.1% (P < 0.005) in the GM and VL, respectively. No changes were observed in the TA and BB muscles. L (f) and theta decreased by 4.8 +/- 5.0% (P < 0.05) and 14.3 +/- 6.8% (P < 0.005) in the GM and by 5.9 +/- 5.3% (P < 0.05) and 13.5 +/- 16.2% (P < 0.005) in the VL, again without any changes in the TA and BB muscles. The finding that amongst the antigravity muscles of the lower limbs, the GM deteriorated to a greater extent than the VL is possibly related to the differences in relative load that this muscle normally experiences during daily loading. The dissimilar response in antigravity and non-antigravity muscles to unloading likely reflects differences in loading under normal conditions. The significant structural alterations of the GM and VL muscles highlight the rapid remodelling of muscle architecture occurring with disuse.     

Are the force characteristics of synchronous handcycling affected by speed and the method to impose power?

ObjectiveTo investigate the influence of exercise conditions (speed and method to impose power) on the applied force, force effectiveness and distribution of work during handcycling.MethodTen able-bodied men performed handcycling on a treadmill. To test the effect of speed, subjects propelled at different velocities (1.38 m/s, 1.66 m/s, 1.94 m/s) with a constant power output (35 W). To test the effect of method to impose power, subjects cycled at a constant speed (1.66 m/s) and different power outputs imposed by incline (1%, 2.5%, 4%) versus pulley system (simulated resistance of incline conditions). From the applied forces, fraction of effective force and work production over the propulsion cycle were calculated.ResultsWhile total force (24.2 to 18.2 N) and tangential force (20.0 to 13.5 N) decreased significantly with higher speed, no change in lateral force was observed (3.5 to 2.8 N). This resulted in a significant decrease of effectiveness (82.6 to 72.9%) and in a change of relative work distribution over the propulsion cycle (44 to 29.8 J). While cycling with the highest velocity, compared to the lower velocities, more work was achieved during pulling and pressing and less work was produced while lifting the crank. No significant differences between the two methods to impose power were found in any parameter (p < 0.05).ConclusionsWhen propelling at equal power output, speed influences the force characteristics of handcycling and should be considered when analyzing force application. Since there is no difference in the force characteristics between propelling at an incline versus ground-level, results of studies examining handbike propulsion with either of these methods are largely comparable.     

Acute effects of different set configurations during a strength-oriented resistance training session on barbell velocity and the force–velocity relationship in resistance-trained males and females

Purpose

This study explored the acute effects of strength-oriented resistance training sessions performed using three different set configurations on barbell velocity and the force–velocity (F–v) relationship of upper-body muscles in men and women.

Method

Thirteen men (age: 23.8 ± 2.5 years; 6-repetition maximum [6RM] load: 73.4 ± 15.6 kg) and 13 women (age: 21.5 ± 1.4 years; 6RM load: 32.8 ± 5.2 kg) performed 24 repetitions with a 6RM load during the bench press exercise using traditional (TR: 6 sets of 4 repetitions with 3 min of rest between sets), cluster (CL: 6 sets of 4 repetitions with 15 s of intra-set rest every two repetitions and 2 min and 45 s of rest between sets) and inter-repetition rest (IRR: 1 set of 24 repetitions with 39 s of rest between repetitions) set configurations. The F–v relationship parameters [maximum force (F₀), maximum velocity (v₀) and maximum power (P_max)] were determined before and after each training session.

Results

The average training velocity did not differ between the three set configurations (p = 0.234), but the IRR set configuration generally provided higher velocities during the last repetition of each set. Significant decreases in F₀ (p = 0.001) and P_max (p = 0.024) but not in v₀ (p = 0.669) were observed after the training sessions. Comparable velocity loss was observed for men and women (− 12.1% vs. − 11.3%; p = 0.699).

Conclusions

The administration of very short intra-set rest periods does not allow for the attainment of higher velocities than traditional set configurations during strength-oriented resistance training sessions conducted with the bench press exercise when the work-to-rest ratio is equated.

     

Influence of muscle fibre type and pedal rate on the V̇O2-work rate slope during ramp exercise

We hypothesised that the ratio between the increase in oxygen uptake and the increase in work rate (O₂/WR) during ramp cycle exercise would be significantly related to the percentage type II muscle fibres at work rates above the gas exchange threshold (GET) where type II fibres are presumed to be active. We further hypothesised that ramp exercise at higher pedal rates, which would be expected to increase the proportional contribution of type II fibres to the total power delivered, would increase the O₂/WR slope at work rates above the GET. Fourteen healthy subjects [four female; mean (SD): age 25 (3) years, body mass 74.3 (15.1) kg] performed a ramp exercise test to exhaustion (25 W min^–1) at a pedal rate of 75 rev min^–1, and consented to a muscle biopsy of the vastus lateralis. Eleven of the subjects also performed two further ramp tests at pedal rates of 35 and 115 rev min^–1. The O₂/WR slope for exercise <GET (S ₁) was significantly correlated with O₂ peak in ml kg^–1 min^–1 (r=0.60; P<0.05), whereas the O₂/WR slope for exercise >GET (S ₂) was significantly correlated to percentage type II fibres (r=0.54; P=0.05). The ratio between the O₂/WR slopes for exercise above and below the GET (S ₂/S ₁) was significantly greater at the pedal rate of 115 rev min^–1 [1.22 (0.09)] compared to pedal rates of 35 rev min^–1 [0.96 (0.02)] and 75 rev min^–1 [1.09 (0.05), (P<0.05)]. The greater increase in S ₂ relative to S ₁ in subjects (1) with a high percentage type II fibres, and (2) at a high pedal rate, suggests that a greater recruitment of type II fibres contributes in some manner to the xs O₂ observed during ramp exercise.     

Effects of concentric and repeated eccentric exercise on muscle damage and calpain–calpastatin gene expression in human skeletal muscle

The purpose of this study was to compare the responsiveness of changes in Ca²⁺-content and calpain–calpastatin gene expression to concentric and eccentric single-bout and repeated exercise. An exercise group (n = 14) performed two bouts of bench-stepping exercise with 8 weeks between exercise bouts, and was compared to a control-group (n = 6). Muscle strength and soreness and plasma creatine kinase and myoglobin were measured before and during 7 days following exercise bouts. Muscle biopsies were collected from m. vastus lateralis of both legs prior to and at 3, 24 h and 7 days after exercise and quantified for muscle Ca²⁺-content and mRNA levels for calpain isoforms and calpastatin. Exercise reduced muscle strength and increased muscle soreness predominantly in the eccentric leg (P < 0.05). These responses as well as plasma levels of creatine kinase and myoglobin were all attenuated after the repeated eccentric exercise bout (P < 0.05). Total muscle Ca²⁺-content did not differ between interventions. mRNA levels for calpain 2 and calpastatin were upregulated exclusively by eccentric exercise 24 h post-exercise (P < 0.05), with no alteration in expression between bouts. Calpain 1 and calpain 3 mRNA did not change at any specific time point post-exercise for either intervention. Our mRNA results suggest a regulation on the calpain–calpastatin expression response to muscle damaging eccentric exercise, but not concentric exercise. Although a repeated bout effect was demonstrated in terms of muscle function, no immediate support was provided to suggest that regulation of expression of specific system components is involved in the repeated bout adaptation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.