Changes In Maximal Voluntary Contraction Research Articles

Activation of skeletal muscle mechanoreceptors and nociceptors reduces the exercise performance of the contralateral homologous muscles.

Increasing evidence suggests that activation of muscle nerve afferents may inhibit central motor drive, affecting contractile performance of remote exercising muscles. While these effects are well documented for metaboreceptors, very little is known about the activation of mechano- and mechano-nociceptive afferents on performance fatigability. Therefore, the purpose of the present study was to examine the influence of mechanoreceptors and nociceptors on performance fatigability. Eight healthy young males undertook four randomized experimental sessions on separate occasions in which the experimental knee extensors were: a) resting (CTRL), b) passively stretched (ST), c) resting with DOMS (DOMS), or d) passively stretched with DOMS (DOMS+ST), while the contralateral leg performed an isometric time to task failure (TTF). Changes in maximal voluntary contraction (ΔMVC), potentiated twitch force (ΔQtw,pot) and voluntary muscle activation (ΔVA) were also assessed. TTF was reduced in DOMS+ST (-43%) and ST (‑29%) compared with CTRL. DOMS+ST also showed a greater reduction of VA (-25% vs ‑8%, respectively) and MVCcompared with CTRL (‑28% vs -45%, respectively). RPE was significantly increased at the initial stages (20-40-60%) of the TTF in DOMS+ST compared with all conditions. These findings indicate that activation of mechanosensitive and mechano-nociceptive afferents of a muscle with DOMS reduces TTF of the contralateral homologous exercising limb, in part by reducing VA so accelerating mechanisms of central fatigue.

Acute neuromuscular, cardiovascular, and muscle oxygenation responses to low-intensity aerobic interval exercises with blood flow restriction.

We investigated the influence of short- and long-interval cycling exercise with blood flow restriction (BFR) on neuromuscular fatigue, shear stress and muscle oxygenation, potent stimuli to BFR-training adaptations. During separate sessions, eight individuals performed short- (24×60s/30s; SI) or long-interval (12×120s/60s; LI) trials on a cycle ergometer, matched for total work. One leg exercised with (BFR-leg) and the other without (CTRL-leg) BFR. Quadriceps fatigue was quantified using pre- to post-interval changes in maximal voluntary contraction (MVC), potentiated twitch force (QT) and voluntary activation (VA). Shear rate was measured by Doppler ultrasound at cuff release post-intervals. Vastus lateralis tissue oxygenation was measured by near-infrared spectroscopy during exercise. Following the initial interval, significant (P<0.05) declines in MVC and QT were found in both SI and LI, which were more pronounced in the BFR-leg, and accounted for approximately two-thirds of the total reduction at exercise termination. In the BFR-leg, reductions in MVC (-28±15%), QT (-42±17%), and VA (-15±17%) were maximal at exercise termination and persisted up to 8min post-exercise. Exercise-induced muscle deoxygenation was greater (P<0.001) in the BFR-leg than CTRL-leg and perceived pain was more in LI than SI (P<0.014). Cuff release triggered a significant (P<0.001) shear rate increase which was consistent across trials. Exercise-induced neuromuscular fatigue in the BFR-leg exceeded that in the CTRL-leg and was predominantly of peripheral origin. BFR also resulted in diminished muscle oxygenation and elevated shear stress. Finally, short-interval trials resulted in comparable neuromuscular and haemodynamic responses with reduced perceived pain compared to long-intervals.

Motor-Respiratory Coupling Improves Endurance Performance during Rhythmic Isometric Handgrip Exercise.

This study aimed to evaluate whether motor-respiratory coupling exists in rhythmic isometric handgrip exercises and its effect on endurance performance. In addition, the mechanism underlying observed effects was to be investigated if higher motor-respiratory coupling rate could enhance endurance performance. Eleven subjects completed three rhythmic isometric handgrip trials to task failure in a randomized manner. After one pretraining session to determine personal grip frequency, one trial was performed without respiration requirement (CON), and two trials were performed with inspiration-motor coupling (IMC) or expiration-motor coupling. Changes in maximal voluntary contraction (MVC) and EMG were used to measure neuromuscular fatigue. Force data during test were used to assess exercise intensity. Another 10 subjects completed electrical stimulation-induced finger flexion and extension during normal inspiration, normal expiration, fast inspiration, fast expiration, and breath holding. Force changes of different breathing conditions were compared. Normalized exercise time to exhaustion was significantly longer in IMC (1.27 ± 0.23) compared with expiration-motor coupling (0.82 ± 0.18) and CON (0.91 ± 0.18, P < 0.001). ΔMVC, grip frequency, force, and EMG indices were not different among conditions (all P > 0.05). Electrical stimulation-induced finger extensor force was significant higher during fast inspiration (1.11 ± 0.09) than normal respiration (1.00 ± 0.05) and fast expiration (0.94 ± 0.08, P < 0.05). IMC is an effective way to improve endurance performance of rhythmic handgrip exercise. This is likely due to a reduction in the energy consumption of motion control, as evidenced by similar peripheral fatigue in different conditions and modulation of corticospinal excitability by respiration.

Effects of motor imagery training on skeletal muscle contractile properties in sports science students.

Studies on motor imagery (MI) practice based on different designs and training protocols have reported changes in maximal voluntary contraction (MVC) strength. However, to date, there is a lack of information on the effects of MI training on contractile properties of the trained muscle. Forty-five physically active sport science students (21 female) were investigated who trained three times per week over a 4-week period in one of three groups: An MI group conducted MI practice of maximal isometric contraction of the biceps brachii; a physical exercise (PE) group physically practiced maximal isometric contractions of the biceps brachii in a biceps curling machine; and a visual imagery (VI) group performed VI training of a landscape. A MVC test of the arm flexors was performed in a biceps curling machine before and after 4 weeks of training. The muscular properties of the biceps brachii were also tested with tensiomyography measurements (TMG). Results showed an interaction effect between time and group for MVC (p=0.027, η 2 = 0.17), with a higher MVC value in the PE group (Δ5.9%) compared to the VI group (Δ-1.3%) (p=0.013). MVC did not change significantly in the MI group (Δ2.1%). Analysis of muscle contractility via TMG did not show any interaction effects neither for maximal radial displacement (p=0.394, η 2 = 0.05), delay time (p=0.79, η 2 = 0.01) nor contraction velocity (p=0.71, η 2 = 0.02). In spite of MVC-related changes in the PE group due to the interventions, TMG measurements were not sensitive enough to detect concomitant neuronal changes related to contractile properties.

Similar strength gains at lower perceived efforts via cluster set vs. traditional home-based online training: A 6 weeks randomized controlled trial.

Cluster Training (CT) has been shown to induce strength at lower perceived efforts compared to traditional training (TRT) with sets performed to repetition failure. These findings have not yet been extended to remote online training in middle-aged to older people. Thus the present study aimed at investigating whether a cluster set online training with bodyweight exercises is similar in its effectiveness a more demanding traditional strength training employed with a traditional set structure. A total of n = 21 participants (14 female, 55 ± 12 years, 76.4 ± 16.1 kg, 1.71 ± 0.10 m, 74 ± 72 min of activity/w) were randomly assigned to either a CT or volume-, load-, and work-to-rest-ratio-matched TRT. After an initial 6-week run-in-phase, all participants were engaged into an online live-instructed full-body workout twice a week (40 min each) for a period of 6 weeks. Rates of perceived efforts (RPE) were assessed for each session (session RPE; sRPE). Changes in maximal voluntary contraction (MVC) at leg press (LP) and abdominal press (AP) as well as one-minute-sit-to-stand and Y-Balance-Test (YBT) were compared between BASELINE and PRE (ΔRUN-IN) and between PRE and POST (ΔINTERVENTION). In LP, TRT showed greater improvements with large effect sizes in ΔINTERVENTION compared to ΔRUN-IN. In CT, greater improvements with moderate effects were found in ΔINTERVENTION compared to ΔRUN-IN. In AP, both CT and TRT showed larger improvements with large effect sizes in ΔINTERVENTION compared to ΔRUN-IN. In YBT, a significant and large main effect for time was found indicating larger improvements for ΔINTERVENTION compared to ΔRUN-IN. CT showed lower sRPE than TRT. Both CT and TRT led to similar adaptations in MVC and balance performance. However, the perceived effort of CT was rated lower than for TRT. Therefore, conducting resistance training with a cluster set structure seems to be a suitable approach for training programs in middle-aged and older people.

Prior Involvement of Central Motor Drive Does Not Impact Performance and Neuromuscular Fatigue in a Subsequent Endurance Task.

This study evaluated whether central motor drive during fatiguing exercise plays a role in determining performance and the development of neuromuscular fatigue during a subsequent endurance task. On separate days, 10 males completed three constant-load (80% peak power output), single-leg knee-extension trials to task failure in a randomized fashion. One trial was performed without preexisting quadriceps fatigue (CON), and two trials were performed with preexisting quadriceps fatigue induced either by voluntary (VOL; involving central motor drive) or electrically evoked (EVO; without central motor drive) quadriceps contractions (~20% maximal voluntary contraction (MVC)). Neuromuscular fatigue was assessed via pre-post changes in MVC, voluntary activation (VA), and quadriceps potentiated twitch force ( Qtw,pot ). Cardiorespiratory responses and rating of perceived exertion were also collected throughout the sessions. The two prefatiguing protocols were matched for peripheral fatigue and stopped when Qtw,pot declined by ~35%. Time to exhaustion was shorter in EVO (4.3 ± 1.3 min) and VOL (4.7 ± 1.5 min) compared with CON (10.8 ± 3.6 min, P < 0.01) with no difference between EVO and VOL. ΔMVC (EVO: -47% ± 8%, VOL: -45% ± 8%, CON: -53% ± 8%), Δ Qtw,pot (EVO: -65% ± 7%, VOL: -59% ± 14%, CON: -64% ± 9%), and ΔVA (EVO: -9% ± 7%, VOL: -8% ± 5%, CON: -7% ± 5%) at the end of the dynamic task were not different between conditions (all P > 0.05). Compared with EVO (10.6 ± 1.7) and CON (6.8 ± 0.8), rating of perceived exertion was higher ( P = 0.05) at the beginning of VOL (12.2 ± 1.0). These results suggest that central motor drive involvement during prior exercise plays a negligible role on the subsequent endurance performance. Therefore, our findings indicate that peripheral fatigue-mediated impairments are the primary determinants of high-intensity single-leg endurance performance.

Relationship between neuromuscular fatigue, muscle activation and the work done above the critical power during severe-intensity exercise.

What is the central question of this study? Does the work done above critical power (W') or muscle activation determine the degree of peripheral fatigue induced by cycling time trials performed in the severe-intensity domain? What is the main finding and its importance? Peripheral fatigue increased when power output and muscle activation increased, whereas W' did not change between the time trials. Therefore, no relationship was found between W' and exercise-induced peripheral fatigue such as previously postulated in the literature. In contrast, we found a significant association between EMG amplitude during exercise and exercise-induced reduction in the potentiated quadriceps twitch, suggesting that muscle activation plays a key role in determining peripheral fatigue during severe-intensity exercise. In order to determine the relationship between peripheral fatigue, muscle activation and the total work done above critical power (W'), 10 men and four women performed, on separated days, self-paced cycling time trials of 3, 6, 10 and 15min. Exercise-induced quadriceps fatigue was quantified using pre- to postexercise (15s to 15min recovery) changes in maximal voluntary contraction (MVC) peak force, voluntary activation and potentiated twitch force (QT). Voluntary activation was measured using the interpolated twitch technique, and QT was evoked by electrical stimulations of the femoral nerve. Quadriceps muscle activation was determined using the root mean square of surface EMG of vastus lateralis (VLRMS ), vastus medialis (VMRMS ) and rectus femoris (RFRMS ). Critical power and W' were calculated from the power-duration relationship from the four time trials. Mean power output and mean VLRMS , VMRMS and RFRMS were greater during shorter compared with longer exercise periods (P<0.05), whereas no significant between-trial change in W' was found. The magnitude of exercise-induced reductions in QT increased with the increase in power output (P<0.001) and was associated with mean VLRMS, VMRMS and RFRMS (P<0.001, r2 >0.369) but not W' (P>0.150, r2 <0.044). Reduction in voluntary activation tended (P=0.067) to be more pronounced with the lengthening in time trial duration, whereas no significant between-trial changes in MVC peak force were found. Our data suggest that peripheral fatigue is not related to the amount of work done above the critical power but rather to the level of muscle activation during exercise in the severe-intensity domain.

Airflow restriction mask induces greater central fatigue after a non-exhaustive high-intensity interval exercise.

The airflow restriction mask (ARM) is a practical and inexpensive device for respiratory muscle training. Wearing an ARM has recently been combined with high-intensity interval exercise (HIIE), but its effect on neuromuscular fatigue is unknown. The present study investigated the effects of ARM wearing on neuromuscular fatigue after an HIIE session. Fourteen healthy men performed two HIIE sessions (4×4min at 90% HRmax , 3min recovery at 70% HRmax ) with or without an ARM. Neuromuscular fatigue was quantified via pre- to post-HIIE changes in maximal voluntary contraction (MVC), voluntary activation (VA, central fatigue), and potentialized evoked twitch force at 100, 10, and 1Hz (peripheral fatigue). Blood pH and lactate were measured before and after the HIIE session, while HR, SpO2 , dyspnea, physical sensation of effort (P-RPE), and Task Effort and Awareness (TEA) were recorded every bout. The exercise-induced decrease in MVC was higher (p<0.05) in the ARM (-28±12%) than in the Control condition (-20±11%). The VA decreased (p<0.05) in the ARM (-11±11%) but not in the control condition (-4±5%, p>0.05). Pre- to post-HIIE declines in evoked twitch at 100, 10, and 1Hz were similar (p>0.05) between ARM and control conditions (ARM: -18±10, -43±11 and -38±12%; Control: -18±14, -43±12 and -37±17%). When compared with the control, the HIIE bout wearing ARM was marked by higher heart rate, plasma lactate concentration, dyspnea, P-RPE and TEA, as well as lower SpO2 and blood pH. In conclusion, ARM increases perceptual and physiological stress during a HIIE, which may lead to a greater post-exercise central fatigue.

Neuromuscular responses to isometric, concentric and eccentric contractions of the knee extensors at the same torque-time integral.

The present study compared isometric, concentric and eccentric contractions at the same torque-time integral for changes in neuromuscular fatigue and muscle damage parameters. Healthy men (18-24years) were placed to either isometric (ISO), concentric (CONC), or eccentric (ECC) group (n = 11/group) that performed corresponding contractions of the knee extensors to exert the same amount of torque-time integral (24,427 ± 291 Nm·s). Changes in maximal voluntary contraction (MVC) torque, voluntary activation, evoked torque at 10Hz and 100Hz and its ratio, M-wave amplitude, and muscle soreness were assessed immediately before and after, 1h, 1day and 2days after each exercise, and were compared among the groups. MVC torque decreased immediately after ISO (-17.0 ± 8.3%), CONC (-21.7 ± 11.5%) and ECC (-26.2 ± 15.6%) similarly (p = 0.35), but the decrease sustained longer (p < 0.05) for ECC (2days post-exercise: -12.9 ± 14.8%) and ISO (-5.5 ± 7.9%) than CONC (+ 5.0 ± 11.0%). Muscle soreness developed after ECC (25.1 ± 19.8mm) and ISO (17.5 ± 21.0mm) similarly (p = 0.15). Voluntary activation decreased immediately (-3.7 ± 6.6%) and 1h post-exercise (-4.7 ± 7.6%) for all groups similarly. Electrically evoked forces decreased greater immediately (-30.1 ± 15.6%) and 1h post-exercise (-35.0 ± 12.8%) for ECC than others, and the decrease in 10/100Hz ratio was also greater immediately (-30.5 ± 12.6%) and 1h after ECC (-23.8 ± 10.3%) than others. ISO, CONC and ECC with the same torque-time integral produced similar neuromuscular fatigue at immediately post-exercise, but the force loss was longer-lasting after ISO and ECC than CONC, and the changes in peripheral fatigue parameters were the greatest after ECC, suggesting greater muscle damage.

The effect of acute low-load resistance exercise with the addition of blood flow occlusion on muscle function in boys and men.

In adults, low-load resistance training with blood flow occlusion (BFO) mimics strength increases that occur from high-load training, without the need to experience high mechanical stress. In view of child-adult differences in exercise responses, this study examined whether BFO during exercise elicits differential changes in maximal voluntary contraction (MVC) and electromyographical (EMG) activity in children and adults. Sixteen men (24.4 ± 2.5 years) and 14 boys (10.7 ± 2.0 years) performed low-load resistance exercise (25 repetitions at 35% MVC) of the wrist flexors with and without BFO. MVC wrist flexor force and EMG activity of the flexor carpi radialis (FCR) were obtained at the beginning and end of the exercise. Both groups demonstrated a larger decrease in MVC force following BFO (- 18.6 ± 12.5%) than the control (without BFO) condition (- 6.2 ± 15.0%; p < 0.001). Whereas the men's EMG amplitude increased 16.3 ± 20.5% (p = 0.005) during BFO, the boys' EMG amplitude did not change over time or between conditions. In both groups, the mean power frequency (MPF) of the EMG signal decreased more during BFO (- 20.1 ± 9.6%; p < 0.001) than the control condition (- 5.6 ± 9.7%; p = 0.002). Low-load exercise with BFO resulted in similar neuromuscular responses between boys and men, except for an observed increase in the EMG amplitude in men but not boys. While this result might suggest that men relied on a greater activation of higher-threshold motor units during BFO, it does not explain why there were similar decreases in MPF between groups. Therefore, it remains unclear whether the effectiveness of BFO training is similar for children and adults.

Effect of a 4-week fish oil supplementation on neuromuscular performance after exhaustive exercise in young healthy men

Neuromuscular function is one of the important factors affecting athletic performance. Previous studies have shown that fish oil supplementation can improve performance. This study investigated the effect of fish oil on neuromuscular performance after exhausting exercise. Eighteen healthy men (mean ± standard deviation; age 26.9±2.6 years; weight 78.33±10.42 kg; height 175.8±4.9 cm; body fat percentage 18.40±5.46%) voluntarily participated and were randomly assigned to fish and corn oil groups in a double blind manner. Participants received 6 g/day of oil for 4 weeks, while maintaining baseline diet and training status during the study. Changes in maximal voluntary contraction (MVC) of the tibialis anterior muscle, neuromuscular propagation of tibialis anterior muscle (M-wave), corticospinal excitability (MEP: motor evoked potential), and the rate of perceived exertion (RPE) were evaluated before and after supplementation in response to a modified Bruce exhausting protocol. Group differences in changes in each variable following supplementation were assessed by two-way analysis of variances (ANOVA). Compared to corn oil, fish oil demonstrated less perceived exertion at the end of exhaustive exercise (F=9.72, P=0.001) after supplementation, and normalised MEP to M-wave showed a trend (F=3.83, P=0.071). However, M-wave peak to peak amplitudes changes were not significant between the groups (P&gt;0.05). In addition, significant differences were observed between baseline MVC values of the group following supplementation. Thus, it seems that fish oil can improve corticospinal excitability, thereby improving neuromuscular function in exhausting activities. Therefore, fish oil supplementation may be recommended to increase performance in activities otherwise limited. However, the mechanism underlying this effect remains to be elucidated.

Do Decreases In Voluntary Activation Account For Fatigability Differently In Males And Females?

Muscular fatigue has been reported to have varying effects depending on sex. Both males and females incur deficits in strength resulting from strenuous activity but males suffer greater relative deficits. Similarly, in a fatigued state, males may be relatively less able to activate muscles. PURPOSE: We sought to determine whether the decrease in strength that males and females suffer is related to changes in their voluntary activation (%VA). METHODS: Twenty-two untrained, college-aged, males (11) and females (11) participated. Subject’s dominant lower leg was strapped to an attachment set at an angle of 110° (180° = full extension) for isometric knee extensions. At pretesting, subjects performed maximal voluntary contractions (MVC) and the interpolated twitch technique was applied to assess %VA. Following initial testing, a fatiguing protocol was performed which consisted of 20 six-second MVCs with 3 seconds in between. In the fatigued state, subjects again performed an MVC and %VA was assessed. Linear regression was performed to determine if the variance in fatigability, as measured by change in MVC, can be accounted for by changes in %VA for each sex. RESULTS: Regression showed that 15.3% and 1.1% of the variance in force loss could be explained by changes in %VA in males and females, respectively. However, neither of these models were significant (p = 0.233 and p = 0.760). The results are shown in the figure below for both males (circles) and females (triangles). A 2-way mixed-factorial ANOVA showed neither a group × time interaction (p = 0.296), nor a main effect for time (p = 0.288) for %VA. CONCLUSIONS: The findings suggest that voluntary activation was not responsible for the force loss with fatigue in either males or females. For the females, this could be partially due to the fact that many of them had minimal changes in MVC from the fatigue protocol, whereas all of the males showed at least a 10% deficit. However, there were no differences in %VA between males and females.

The magnitude of neuromuscular fatigue is not intensity dependent when cycling above critical power but relates to aerobic and anaerobic capacities.

What is the central question of this study? Is the magnitude of neuromuscular fatigue dependent upon exercise intensity above critical power (CP) when W' (the curvature constant of the power-duration relationship) is depleted? What is the main finding and its importance? The magnitude of neuromuscular fatigue is the same after two bouts of supra-CP cycling (3 versus 12min) when controlling for W' depletion but is larger for individuals of greater anaerobic capacity after the shorter bout and smaller for individuals of greater aerobic capacity after the longer exercise bout. These findings provide new insight into the mechanisms underpinning exercise above CP. The aim of the present study was to test whether the development of neuromuscular fatigue within the severe-intensity domain could be linked to the depletion of the curvature constant (W') of the power-duration relationship. Twelve recreationally active men completed tests to determine peak oxygen consumption, critical power (CP) and W', followed by two randomly assigned constant-load supra-CP trials set to deplete W' fully in 3 (P-3) and 12min (P-12). Pre- to postexercise changes in maximal voluntary contraction, potentiated quadriceps twitch force evoked by single (Qpot ) and paired high- (PS100) and low-frequency (PS10) stimulations and voluntary activation were determined. Cycling above CP reduced maximal voluntary contraction (P-3, -20± 10% versus P-12, -15± 7%), measures associated with peripheral fatigue (Qpot , -35± 13 versus -31± 14%; PS10, -38± 13 versus -37± 17%; PS100, -18± 9 versus -13± 8% for P-3 and P-12, respectively) and voluntary activation (P-3, -12± 3% versus P-12, -13± 3%; P< 0.05), with no significant difference between trials (P> 0.05). Changes in maximal voluntary contraction and evoked twitch forces were inversely correlated with CP and peak oxygen consumption after P-12, whereas W' was significantly correlated with changes in Qpot and PS10 after P-3 (P< 0.05). Therefore, the magnitude of neuromuscular fatigue does not depend on exercise intensity when W' is fully exhausted during severe-intensity exercise; nonetheless, exploration of inter-individual variations suggests that mechanisms underpinning exercise tolerance within this domain differ between short- and long-duration exercise.

Elastic band exercise induces greater neuromuscular fatigue than phasic isometric contractions

This study investigated the neuromuscular fatigue following an elastic band exercise (EB) of the plantar flexors, compared to an intermittent phasic isometric exercise (ISO). Eleven young healthy males (age: 24.2 ± 3.7) took part in the study, consisting of one experimental session involving two 5-min fatiguing protocols separated by 20 min rest and performed randomly. Both exercises were performed at maximal motor output of the plantar flexor muscles, EMG being used as a feedback signal. Neuromuscular fatigue was assessed through changes in maximal voluntary contraction (MVC) and in evoked responses of soleus and gastrocnemii muscles to posterior tibial nerve stimulation (H-reflex, M-wave, V-wave). Both conditions induced significant decrease in MVC force, but to a greater extent after EB (−20.0 ± 5.1%, P < 0.001) than after ISO (−12.3 ± 4.6%, P = 0.037). While no effect was observed in M-wave amplitude after both exercises, EB resulted in greater decrease of normalized H-reflexes compared to isometric condition. Normalized V-wave significantly decreased only after EB. As a conclusion, the greater fatigability found after EB as compared to ISO was underlain by muscular as well as nervous factors. This higher impact was attributed to the dynamic nature of elastic band exercise as compared to isometric contractions.

The effect of motivational climate and conscientiousness on athletes’ maximal voluntary contraction level of biceps brachii muscle

We investigated the effect of induced motivational climates (a mastery climate and a performance climate) on maximal voluntary contraction (MVC) level of the biceps brachii muscle. We also aimed to explore whether motivational orientations, together with conscientiousness, are associated with MVC level in mastery and performance climate conditions. The sample consisted of 53 college student athletes ranging in age from 20 to 26. Participants first completed the Task and Ego Orientation in Sport Questionnaire and items relating to conscientiousness from the Short Form of the Five Factor Personality Inventory. Then, during isometric elbow flexion, MVCs were measured in a neutral condition. Afterwards, participants were informed of their MVC levels measured in the neutral condition via biofeedback software, and randomly assigned to either the mastery or the performance condition. Participants in the mastery climate condition were instructed to exceed their own highest MVC level observed in the neutral condition. In contrast, participants in the performance climate condition were instructed to exceed an unrealistic MVC level described as the best ever recorded so far. Results indicated that percentage change in MVC differed significantly between the mastery and performance climate conditions. Specifically, while there was a 13.5% increase in MVC value in the performance climate condition, there was an 8.8% decrease in the mastery climate condition. Results also showed that regardless of motivational climate, the percentage change in MVC was unrelated to motivational orientations and conscientiousness.

Isometric parameters in the monitoring of maximal strength, power, and hypertrophic resistance-training.

This study monitored strength-training adaptations via isometric parameters throughout 2 × 10 weeks of hypertrophic (HYP I-II) or 10 weeks maximum strength (MS) followed by 10 weeks power (P) training with untrained controls. Trainees performed bilateral isometric leg press tests analyzed for peak force (maximal voluntary contraction (MVC)) and rate of force development (RFD) every 3.5 weeks. These parameters were compared with dynamic performance, voluntary and electrically induced isometric contractions, muscle activity, and cross-sectional area (CSA) in the laboratory before and after 10 and 20 weeks. RFD increased similarly during the first 7 weeks (HYP I, 44% ± 53%; MS, 48% ± 55%, P < 0.05), but RFD continued to increase up to 65% ± 61% from baseline (P < 0.01) only during P. These increases were concomitant with enhanced dynamic performances of 1-repetition maximum (1RM) (HYP I, 8% ± 6%; MS, 11% ± 6%, P < 0.001), and explosive repetitions during P (11% ± 15%, P < 0.05). Time to reach peak RFD differed (P < 0.001) between HYP (mean 42 ± 20 ms) and MS-P (mean 31 ± 12 ms) groups because of training. The changes in MVC correlated with the changes in CSA during weeks 1-20 (HYP I-II, r = 0.664; MS-P, r = 0.595, P ≤ 0.05), as well as changes in 1RM (r = 0.724, P < 0.05) during weeks 11-20 (HYP II). Muscle activity increased during MS and P only. Both MVC and RFD improvements reflected combinations of central and peripheral adaptations. RFD parameters may be effective tools to evaluate adaptations, particularly during maximal strength/power training, while MVC cannot distinguish between strength or muscle mass changes. Monitoring RFD provided important information regarding plateaus in RFD improvement, which were observed in dynamic explosive performances after HYP II compared with P.

Sex Differences in the Associations between L-Arginine Pathway Metabolites, Skeletal Muscle Mass and Function, and their Responses to Resistance Exercise, in Old Age.

The current study was designed to explore the associations between L-arginine metabolites and muscle mass and function in old age, which are largely unknown. The study used a randomised, double-blind, placebo-controlled design. The study was carried out in a laboratory setting. 50 healthy older adults [median age 70 years (IQR 67-73); 27 males]. Participants undertook an 18-week resistance exercise program, and a nutritional intervention (fish oil vs. placebo). Serum homoarginine, ornithine, citrulline, asymmetric dimethylarginine (ADMA), NG-monomethyl-L-arginine (L-NMMA), and symmetric dimethylarginine (SDMA), maximal voluntary contraction (MVC) and isokinetic torque of the knee extensors at 30° s-1 (MIT), muscle cross sectional area (MCSA) and quality (MQ) were measured at baseline and after the intervention. No significant exercise-induced changes were observed in metabolite concentrations. There were significant sex differences in the associations between metabolites and muscle parameters. After adjusting for age, glomerular filtration rate and fish oil intervention, citrulline (P=0.002) and ornithine (P=0.022) were negatively associated with MCSA at baseline in males but not females. However, baseline citrulline was negatively correlated with exercise-induced changes in MVC (P=0.043) and MQ (P=0.026) amongst females. Furthermore, amongst males, baseline homoarginine was positively associated with exercise-induced changes in MVC (P=0.026), ADMA was negatively associated with changes in MIT (P=0.026), L-NMMA (p=0.048) and ornithine (P<0.001) were both positively associated with changes in MCSA, and ornithine was negatively associated with changes in MQ (P=0.039). Therefore, barring citrulline, there are significant sex differences in the associations between L-arginine metabolites and muscle mass and function in healthy older adults. These metabolites might enhance sarcopenia risk stratification, and the success of exercise programs, in old age.

Inflammation Relates to Resistance Training-induced Hypertrophy in Elderly Patients.

Aging is associated with a gradual loss of muscle mass, which some have suggested to be accelerated by short periods of muscle disuse due to medical illness. We investigated the effect of hospitalization on skeletal muscle mass in acutely ill geriatric patients with focus on the relationship between systemic inflammatory marker C-reactive protein (CRP) and changes in muscle mass, as well as the influence of resistance training upon muscle mass. Unilateral leg press resistance exercise was conducted daily during the hospital period. Outcomes included changes in whole body and regional lean mass, maximal voluntary contraction of the knee extensors, leg extension power, and functional performance. Activity level was measured using ActivPAL accelerometers, and CRP levels were obtained from blood samples. Sixteen subjects completed the study (eight men and eight women, age = 84.8 ± 1.9 yr, mean ± SE). Lean mass at the midthigh region of the trained leg increased by 2.4% ± 1.1% (P < 0.05) after the intervention period. There was a negative association between changes in midthigh lean mass of the trained leg and CRP (rs = -0.53, P < 0.05). Leg extension power increased significantly in both legs (P < 0.05), with no difference observed between legs. There were no changes in maximal voluntary contraction or functional performance. Muscle mass is not significantly lost during short-term hospitalization of relatively high functioning and active geriatric patients although our findings are potentially affected by changes in hydration status. Resistance training during hospitalization increases skeletal muscle mass, and patients with high levels of systemic inflammation demonstrate less ability to increase or preserve muscle mass in response to resistance training during illness.

Effect of strength training on muscle architecture (review)

Muscle architecture is among the most important factors that determine the function of muscles. Muscle architecture is the “organizer” of muscle fibres in muscle strength generating relative line and includes several important aspects: 1) normalized fibre length, 2) pennation angle, and 3) physiological cross-sectional area. Architectural changes in muscles immediately respond to resistance training, but it is not entirely dependent on muscle contraction mode. To the date, we very poorly understand architectural parameters for each muscle; thus, further studies are needed to explore the architecture of individual muscles and further to expand our understanding of this important organizer of muscle fibres. The purpose of the article is to examine the relationship between strength training and muscle structures. Method chosen: analysis of scientific literature. Results and conclusions. In general, contemporary scientific research confirms in the 80-ies identified circumstantial evidence in favour of muscle architecture changes with the help of strength training. Hypertrophy of the muscle increases the angles of pennate muscles. The more muscle hypertrophy evolves, the less specific voltage occurs. Increased muscle volume in the eccentric training is closely related to increasing length of the beams, but pennation angle is not changed. The level of tension is responsible for the change in maximal voluntary contraction. Strength training is needed to formation of skeletal muscles, increase of strength and quality of muscles as well as for muscle morphology in the elderly. Architectural changes in the muscles immediately respond to weight training, but it is absolutely independent from muscle contraction mode. Age significantly affects the architecture of human muscles, and aging leads to negative structural changes of muscle function. Further long-term studies should be conducted to determine exactly, what structures are responsible for the increase in knee range of motion for static stretching.

Stretch training induces unequal adaptation in muscle fascicles and thickness in medial and lateral gastrocnemii.

This study compared adaptations in fascicle lengths, pennation angles, and muscle thickness of the lateral and medial gastrocnemii in response to 6weeks of stretch training. The nondominant plantar flexors of 11 males were stretched five times per week for 6weeks and compared with the contralateral leg and a nonstretched control group of 10 males. During stretch training, instantaneous electromyography was utilized to ensure passive muscle stretch. At baseline, week three, week six and 1week after the conclusion of stretch training, ultrasound was used to measure fascicle lengths, pennation angles, muscle thickness of the lateral gastrocnemius and medial gastrocnemius, and Achilles tendon thickness and length. Plantar flexion torque was measured, and voluntary activation was assessed. Muscle thickness increased 5.6% after 6weeks of stretch training (P=.009). The fascicles in the lateral gastrocnemius lengthened to a greater extent than the medial. Overall, fascicles lengthened 25% (P<.001) in the muscle tendon junction and 5.1% (P<.001) in the muscle belly. Pennation angles were unchanged in the medial gastrocnemius but decreased in the lateral gastrocnemius 7.1% (P=.02). There was no change in maximal voluntary contraction, voluntary activation, tendon length, or thickness. This study demonstrates that stretch training is a viable modality to alter muscle architecture of the human gastrocnemius through lengthening of muscle fascicles, decreasing pennation angles, and increasing muscle thickness, albeit adaptations are unequal between the lateral and medial heads.