Central and peripheral contributions to fatigue after electrostimulation training

PURPOSE: We examined the effect of 4 (WK4) and 8 wk (WK8) of neuromuscular electrical stimulation (NMES) training on both endurance time and mechanisms contributing to task failure. METHODS: Ten males performed a fatiguing isometric contraction with the knee extensor muscles at 20% of maximal voluntary contraction (MVC) until exhaustion before (B), at WK4, and at WK8 of NMES training. The electromyographic (EMG) activity and muscle activation obtained under MVC were recorded before and after the fatiguing task to assess central fatigue. Torque and EMG responses obtained under electrically evoked contractions were examined before and after the fatiguing task to analyze peripheral fatigue. RESULTS: Knee extensor MVC torque increased significantly between B and WK4 (+16%), between WK4 and WK8 (+10%), and between B and WK8 (+26%), which meant that the average target torque sustained during the fatiguing contraction increased between the testing sessions. Endurance time decreased significantly over the three sessions (493+/-101 s at B, 408+/-159 s at WK4, and 338+/-126 s at WK8) despite a similar reduction in knee extensor MVC (approximately 25%). Negative correlations were found between endurance time absolute changes and target torque absolute gains. Average EMG activity of the knee extensor muscles was lower after training, but the mean rate of increase was similar over the three sessions. Single-twitch contractile properties were not affected by the task. CONCLUSION: We conclude that the endurance time was shorter after 4 and 8 wk of NMES training, and this was associated with higher absolute contraction intensity. Despite endurance time reduction, NMES training did not affect the amount of fatigue at exhaustion nor the central and peripheral contributions to fatigue.     

Effect of high-intensity intermittent cycling sprints on neuromuscular activity

High-intensity intermittent sprints induce changes in metabolic and mechanical parameters. However, very few data are available about electrical manifestations of muscle fatigue following such sprints. In this study, quadriceps electromyographic (EMG) responses to repeated all-out exercise bouts of short duration were assessed from maximal voluntary isometric contractions (MVC) performed before and after sprints. Twelve men performed ten 6-s maximal cycling sprints, separated by 30-s rest. The MVC were performed pre-sprints ( pre), post-sprints ( post), and 5 min post-sprints ( post5). Values of root-mean-square (RMS) and median frequency (MF) of vastus lateralis (VL) and vastus medialis (VM) were recorded during each MVC. During sprints, PPO decreased significantly in sprints 8, 9, and 10, compared to sprint 1 (- 8 %, - 10 %, and - 11 %, respectively, p < 0.05). Significant decrements were found in MVC post (- 13 %, p < 0.05) and MVC post5 (- 10.5 %, p < 0.05) compared to MVC pre. The RMS value of VL muscle increased significantly after sprints (RMS pre vs. RMS post: + 15 %, p < 0.05). Values of MF decreased significantly in both VL and VM after sprints. In conclusion, our results indicate that the increase in quadriceps EMG amplitude following high-intensity intermittent short sprints was not sufficient to maintain the required force output. The concomitant decrease in frequency components would suggest a modification in the pattern of muscle fiber recruitment, and a decrease in conduction velocity of active fibers.     

The effects of rest interval and resistance training on quadriceps femoris muscle. Part II: EMG and perceived exertion

AIM: The purpose of this study was to examine the effects of rest interval on quadriceps femoris muscle activation and perceived exertion, during short-term resistance training. METHODS: Vastus medialis (VM) and vastus lateralis (VL) muscle electromyograms (EMG) were assessed in 15 males during a sustained 80% maximal voluntary contraction (MVC). During the pre-training evaluation, the absolute value of the 80% MVC (N.m) and contraction duration (s) was performed at 2, 4, and 6 weeks during the training period. Perceived exertion was measured via the Borg category-ratio scale every 5 s during the 80% MVC. Subjects were randomly assigned to 3 groups: group 1 received a 40 s rest interval in between exercise sets, group 2 received a rest period of 160 s, and the control group did not participate in training. Groups 1 and 2 performed isokinetic knee extensions at 180 deg.s(-1) 2 days per week for 6 weeks. RESULTS: The results demonstrated a significant decrease in VM EMG within the initial portion of the 80% MVC across the training period in the short rest interval group. The long rest interval and control groups showed no significant changes in VM EMG during 1st part of the contraction across the training period, whereas the control group exhibited a significant reduction in VL EMG across weeks 4 to 6. VL EMG increased during the 80% MVC in the control group across the training period. VM EMG increased during the sustained contractions in the long rest interval and control groups across the training period. The perceived exertion response was lower in the 1st part of the 80% MVC in the short and long rest interval groups, but not in the control group, across the training period. The results also showed a significant decrease in perceived exertion at the end of the sustained contraction in the short rest interval group, but not in the long rest interval group or the control group. CONCLUSIONS: The findings from this study suggest that the application of relatively short rest intervals in between sets of resistance exercise induced a greater neuromuscular response of the VM muscle during short-term training.     

Vitamin and mineral supplementation and neuromuscular recovery after a running race

PURPOSE: This double-blind study investigated the effects of vitamin and mineral complex supplementation on the neuromuscular function of the knee-extensor muscles after a prolonged trail running race. METHODS: Twenty-two well-trained endurance runners took either placebo (Pl group) or vitamins and minerals (Vm group) for 21 d before the race and for 2 d after the race. Maximal voluntary contractions (MVC) and surface EMG activity of the vastus lateralis (VL) muscle were recorded before (pre) and 1 h (post), 24 h (post 24) and 48 h (post 48) after the race. Central activation ratio (CAR), neural (M-wave), and contractile (muscular twitch) properties of the quadriceps muscles were analyzed using electrical stimulation techniques. RESULTS: The knee-extensor MVC was significantly (P < 0.01) reduced after exercise for both groups (Vm: 36.5 +/- 3.0 %; Pl: 36.9 +/- 2.1%), but MVC recovery was greater for Vm than Pl after 48 h (11%, P < 0.05). The reduced MVC after exercise was associated with a significant reduction in maximal EMG normalized to the M-wave in VL muscle and in CAR for both groups. Characteristics of the muscular twitch were not significantly altered for either groups, whereas M-wave duration increased significantly (P < 0.05) after exercise. CONCLUSIONS: The reduction of MVC immediately after the race appeared to result from peripheral mechanisms such as a failure in muscle membrane excitation and, to a lesser extent, from reduced central activation. The cause of the depressed MVC 24 h after the race seemed to be located within the muscle itself. A dietary supplementation of a vitamin and mineral complex does not attenuate the loss of contractile function immediately after the running exercise, and it may accelerate the recovery of maximal force capacity.     

Evidence of neuromuscular fatigue after prolonged cycling exercise

PURPOSE: The purpose of this study was to analyze the effects of prolonged cycling exercise on metabolic, neuromuscular, and biomechanical parameters. METHODS: Eight well-trained male cyclists or triathletes performed a 2-h cycling exercise at a power output corresponding to 65% of their maximal aerobic power. Maximal concentric (CON; 60, 120, 240 degrees x s(-1)), isometric (ISO; 0 degrees s(-1)), and eccentric (ECC; -120, -60 degrees x s(-1)) contractions, electromyographic (EMG) activity of vastus lateralis (VL) and vastus medialis (VM) muscles were recorded before and after the exercise. Neural (M-wave) and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed using electrical stimulation techniques. RESULTS: Oxygen uptake (VO2), minute ventilation (VE), and heart rate (HR) significantly increased (P < 0.01) during the 2-h by, respectively, 9.6%, 17.7%, and 12.7%, whereas pedaling rate significantly decreased (P < 0.01) by 21% (from 87 to 69 rpm). Reductions in muscular peak torque were quite similar during CON, ISO, and ECC contractions, ranging from 11 to 15%. M-wave duration significantly increased (P < 0.05) postexercise in both VL and VM, whereas maximal amplitude and total area decreased (VM: P < 0.05, VL: NS). Significant decreases in maximal twitch tension (P < 0.01), total area of mechanical response (P < 0.01), and maximal rate of twitch tension development (P < 0.05) were found postexercise. CONCLUSIONS: A reduction in leg muscular capacity after prolonged cycling exercise resulted from both reduced neural input to the muscles and a failure of peripheral contractile mechanisms. Several hypothesis are proposed to explain a decrease in pedaling rate during the 2-h cycling with a constancy of power output and an increase in energy cost.     

Why does knee extensor muscles torque decrease after eccentric-type exercise?

AIM: The purpose of this study was to re-examine central and peripheral origins of neuromuscular fatigue after a highly strenuous eccentric exercise of the knee extensor muscles (KE) using both voluntary/evoked contractions and electromyographic recordings (EMG). METHODS: Before, and 30 min after 15 min of intermittent one-logged downhill running, maximal percutaneous electrical stimulations (single twitch, 0.5 s tetanus at 20 Hz and 80 Hz) were applied to the femoral nerve of 10 male subjects. Electrically evoked superimposed twitches were delivered during isometric maximal voluntary contraction (MVC) to determine maximal voluntary activation (%VA). Vastus lateralis (VL), vastus medialis (VM) and biceps femoris (BF) EMG were recorded during MVC and quantified using the root mean square (RMS) value. M-wave characteristics were also determined. RESULTS: KE MVC and %VA decreased significantly with fatigue (-19.6+/-6.1%; P<0.001 and -7.8+/-6.6%; P<0.01, respectively). Peak tetanus tension at 20 and 80 Hz (P20 and P80, respectively) declined (P<0.001), concurrently with a decrement of the P20 x P80(-1) ratio (-37.3+/-16.6%; P<0.001). Antagonist muscle coactivation, RMS to M-wave peak-to-peak amplitude and MVC x P80(-1) ratios were unchanged after the fatiguing exercise. CONCLUSIONS: The results reveal that part of the large loss in MVC may have a central origin but most of the MVC decrement is due to the presence of low-frequency fatigue while possible contractile failure cannot be excluded.     

Quadriceps EMG/force relationship in knee extension and leg press

PURPOSE: This study compared the relationship between surface electromyographic (EMG) activity and isometric force of m. quadriceps femoris (QF) in the single-joint knee extension (KE) and the multi-joint leg press (LP) exercises. METHODS: Nine healthy men performed unilateral actions at a knee angle of 90 degrees at 20, 40, 60, 80, and 100% of maximal voluntary contraction (MVC). EMG was measured from m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), and m. biceps femoris (BF). RESULTS: There were no differences in maximum EMG activity of individual muscles between KE and LP. The QF EMG/force relationship was nonlinear in each exercise modality. VL showed no deviation from linearity in neither exercise, whereas VM and RF did. BF activity increased linearly with increased loads. CONCLUSIONS: The EMG/force relationship of all quadricep muscles studied appears to be similar in isometric multi-joint LP and single-joint KE actions at a knee angle of 90 degrees. This would indicate the strategy of reciprocal force increment among muscles involved is comparable in the two models. Furthermore, these data suggest a nonuniform recruitment pattern among the three superficial QF muscles and surface EMG recordings from VL to be most reliable in predicting force output.     

Effect of knee joint angle on neuromuscular activation of the vastus intermedius muscle during isometric contraction

The purpose of this study was to compare the relationship between surface electromyography (EMG) and knee joint angle of the vastus intermedius muscle (VI) with the synergistic muscles in the quadriceps femoris (QF) muscle group. Fourteen healthy men performed maximal voluntary contractions during isometric knee extension at four knee joint angles from 90°, 115°, 140°, and 165° (180° being full extension). During the contractions, surface EMG was recorded at four muscle components of the QF muscle group: the VI, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles. The root mean square of the surface EMG at each knee joint angle was calculated and normalized by that at a knee joint angle of 90° for individual muscles. The normalized RMS of the VI muscle was significantly lower than those of the VL and RF muscles at the knee joint angles of 115° and 165° and those of the VL, VM, and RF muscles at the knee joint angle of 140° (P<0.05). The present results suggest that the neuromuscular activation of the VI muscle is regulated in a manner different from the alteration of the knee joint angle compared with other muscle components of the QF muscle group.     

Submaximal motor unit firing rates after 8 wk of isometric resistance training

PURPOSE: The purpose of this study was to test the hypothesis that average motor unit firing rates change in parallel with the contractile properties of vastus lateralis following 8 wk of isometric resistance training. METHODS: The firing rates from more than 400 motor units of vastus lateralis were obtained during voluntary isometric contractions of 50% MVC, before and again after training in male subjects (N = 10) and their untrained controls (N = 10). Single motor unit spike trains were recorded with tungsten microelectrodes. RESULTS: Training resulted in a 36% (P < 0.05) increase in MVC. We also found significant increases (P < 0.05) in maximal twitch amplitude (+17%), time to peak tension (+9%) and the maximal instantaneous rate of contraction (+20%) in the trained leg of the experimental group. Neither the maximal integrated EMG nor the rate of increase of integrated EMG was different after training. There were no significant changes in any of these measures from the untrained leg or the control group. Average firing rates were not different after training despite the increase in twitch contractile speed. CONCLUSION: These findings suggest that the control properties of the nervous system are not altered despite sizable changes in the contractile properties of muscle following 8 wk of resistance training.     

The effects of a prolonged running exercise on strength characteristics

The aim of this study was to examine concentric, isometric, and eccentric strength reductions in the quadriceps muscle following a prolonged running exercise. Before and after a 2 h run (28.4+/-1.4 km) peak torque (PT) of the knee extensors at angular velocities of -120, -90, -60, 0, 60, 120, 180, 240 degrees x s(-1) using an isokinetic dynamometer, electromyographic (EMG) activity of the vastus lateralis (VL) and vastus medialis (VM) muscles and height of a counter movement jump were recorded in twelve well-trained triathletes. Counter movement jump performances decreased by 10% and PT values were all significantly lower (p < 0.01) at each angular velocity following the run. The torque loss was significantly (p < 0.01) greater under eccentric contractions (from 18 to 21%) than under concentric ones (from 11 to 14%). EMG activity (RMS) was lower in both VL and VM muscles after the 2 h run but no difference existed in RMS losses between concentric and eccentric contractions. The present results demonstrate that 1) a prolonged running exercise more greatly affects eccentric force production in the quadriceps muscle, and 2) this specificity seems to be due to an impairment of the muscular contractile mechanism rather than a modification to the neural input.     

Muscle architectural characteristics in young and elderly men and women

The purpose of this study was to compare the muscle architectural characteristics, i. e., muscle thickness, pennation angle, fascicle length, of four different groups comprising a total of 121 men and 190 women, divided according to sex and age (i. e., 20 - 39 yrs and 60 - 85 yrs). Muscle thickness and pennation angles of the vastus lateralis (VL), medial gastrocnemius (MG), long head of triceps brachii (TB) muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Men had significantly greater relative muscle thickness (to limb length) than women, but not for MG. Relative muscle thickness of VL was significantly greater in younger subjects than in elderly (men; p < 0.001, women; p < 0.001), although there were no significant differences in relative muscle thickness of MG and TB between younger and elderly subjects. Men had significantly greater pennation angles than women, but not for MG in elderly subjects. The pennation angle of VL was significantly greater in younger subjects than in elderly (men; p < 0.001, women; p < 0.001), although there were no significant differences in pennation angles of MG and TB between younger and elderly subjects. Women had longer relative fascicle lengths (to limb length) of VL than men (p = 0.048 for younger, p = 0.028 for elderly). These results suggest that the decrease of thickness of the vastus lateralis muscle with aging is significant, and that there is the gender difference in the fascicle length of the vastus lateralis muscle.     

Muscle architectural characteristics in women aged 20-79 years

PURPOSE: The purpose of this study was to investigate the muscle architectural characteristics, i.e., muscle thickness, pennation angle, and fascicle length, in women aged 20-79 yr. METHODS: A total of 224 sedentary healthy women participated in this study. Muscle thickness and pennation angle of the vastus lateralis (VL), medial gastrocnemius (MG), and triceps brachii (TB) muscles were measured by B-mode ultrasonography, and the fascicle length was estimated. RESULTS: Relative muscle thickness of VL and MG decreased significantly with advanced age (VL: P< 0.01, MG: P< 0.05). In addition, the ratio of muscle thickness of VL to that of MG decreased significantly with advanced age (r = -0.206, P< 0.05). The pennation angle decreased significantly with aging for VL (P< 0.001) but not for MG. For TB, no significant age-related changes in relative muscle thickness or pennation angle were observed. There were no significant correlations between age and relative fascicle length (to limb length) in any of the studied muscles. CONCLUSION: These results suggested that the declines in muscle thickness and pennation angle with aging were remarkable in the vastus lateralis muscle and slight in the medial gastrocnemius muscle. For the triceps brachii muscle, the muscle thickness and pennation angle did not decrease with advanced age. Furthermore, no significant age-related changes in relative fascicle length (to limb length) were observed in any of the studied muscles.     

恢复期脑卒中患者膝关节最大等长收缩时大腿肌群表面肌电信号特征研究

目的:探讨脑卒中恢复期偏瘫患者膝屈伸最大等长收缩(maximum isometric voluntary contraction,MIVC)时部分大腿肌肉表面肌电(surfaceelectromyography,sEMG)信号特征,为恢复期脑卒中患者的康复治疗提供客观依据。方法:28例脑卒中患者和20例年龄、性别相匹配的正常对照者。在膝关节屈伸MIVC时记录股内侧肌(vastus medialis,VM)、股直肌(rectus femoris,RF)、股外侧肌(vastus lateralis,VL)和股二头肌(biceps femoris,BF)sEMG信号,计算相应的积分肌电值(integrated EMG,iEMG)、协同收缩率(co-contraction ratio,CR)。结果:伸膝时,患侧VM、RF及VL的iEMG值显著小于正常对照及健侧iEMG(P<0.05);健侧RF的iEMG显著小于正常对照iEMG(P<0.05);屈膝时,患侧BF、VL及RF的iEMG显著小于正常对照(P<0.05)。患侧伸膝CR显著大于健侧及正常对照(P<0.05),患侧屈膝CR大于健侧及正常对照,但无统计学意义(P>0.05)。结论:恢复期脑卒中偏瘫患者双下肢肌肉收缩功能下降,患侧大腿伸肌存在轻度痉挛,肌力训练可作为患者康复训练的重点内容之一。     

Effect of combined electrostimulation and plyometric training on vertical jump height

PURPOSE: This study investigated the influence of a 4-wk combined electromyostimulation (EMS) and plyometric training program on the vertical jump performance of 10 volleyball players. METHODS: Training sessions were carried out three times weekly. Each session consisted of three main parts: EMS of the knee extensor muscles (48 contractions), EMS of the plantar flexor muscles (30 contractions), and 50 plyometric jumps. Subjects were tested before (week 0), during (week 2), and after the training program (week 4), as well as once more after 2 wk of normal volleyball training (week 6). Different vertical jumps were carried out, as well as maximal voluntary contraction (MVC) of the knee extensor and plantar flexor muscles. RESULTS: At week 2, MVC significantly increased (+20% knee extensors, +13% plantar flexors) as compared to baseline ( < 0.05). After the 4-wk training program, different vertical jumps considered were also significantly higher compared to pretraining ( < 0.001), and relative gains were comprised between 8-10% (spike-counter movement jump) and 21% (squat jump). The significant increases in maximal strength and explosive strength produced by the present training program were subsequently maintained after an additional 2 wk of volleyball training. CONCLUSION: EMS combined with plyometric training has proven useful for the improvement of vertical jump ability in volleyball players. This combined training modality produced rapid increases (approximately 2 wk) of the knee extensors and plantar flexors maximal strength. These adaptations were then followed by an improvement in general and specific jumping ability, likely to affect performance on the court. In conclusion, when EMS resistance training is proposed for vertical jump development, specific work out (e.g., plyometric) must complement EMS sessions to obtain beneficial effects.     

Acute fatigue-induced changes in muscle mechanical properties and neuromuscular activity in elite handball players following a handball match

The purpose of the present study was to determine the acute fatigue development in muscle mechanical properties and neuromuscular activity in response to handball match play. Male elite handball players ( n = 10) were tested before and after a simulated handball match for maximal isometric strength [maximal voluntary contraction (MVC)] and rate of force development (RFD) with synchronous electromyography (EMG) recording, while maximal vertical jump parameters were assessed using force plate analysis. Quadriceps and hamstrings MVC and RFD decreased significantly post-match (∼10%, P <0.05 and ∼16–21%, P <0.05, respectively). During quadriceps, MVC mean EMG amplitude [mean average voltage (MAV)] decreased for the vastus lateralis (VL) and rectus femoris (RF) (21–42%, P ≤0.05), while MAV also decreased in the antagonist biceps femoris (BF) muscle (48–55%, P <0.01). During hamstring MVC, MAV was reduced in BF (31%, P <0.01). Maximum EMG amplitude during quadriceps MVC was reduced for the VL (28%, P <0.01) and the RF (5%, P <0.05). During hamstring MVC, maximum EMG was reduced for BF (21%, P <0.01). Post-match maximal jump height was reduced (5.2%, P <0.01), as was also work (6.8%, P <0.01), velocity of center of mass (2.4–4.0%, P <0.01) and RFD (∼30%, P <0.05). In conclusion, maximal (MVC) and rapid muscle force characteristics (RFD, impulse) were acutely affected concurrently with marked reductions in muscle EMG following handball match play, which may potentially lead to impaired functional performance.     

Effects of concurrent exercise training on muscle dysfunction and systemic oxidative stress in older people with COPD

Oxidative stress is associated with disease severity and limb muscle dysfunction in COPD. Our main goal was to assess the effects of exercise training on systemic oxidative stress and limb muscle dysfunction in older people with COPD. Twenty‐nine outpatients with COPD (66‐90 years) were randomly assigned to a 12‐week exercise training (ET; high‐intensity interval training (HIIT) plus power training) or a control (CT; usual care) group. We evaluated mid‐thigh muscle cross‐sectional area (CSA; computed tomography); vastus lateralis (VL) muscle thickness, pennation angle, and fascicle length (ultrasonography); peak VO₂ uptake (VO_2peak) and work rate (W_peak) (incremental cardiopulmonary exercise test); rate of force development (RFD); maximal muscle power (P_max; force‐velocity testing); systemic oxidative stress (plasma protein carbonylation); and physical performance and quality of life. ET subjects experienced changes in mid‐thigh muscle CSA (+4%), VL muscle thickness (+11%) and pennation angle (+19%), VO_2peak (+14%), W_peak (+37%), RFD (+32% to 65%), P_max (+38% to 51%), sit‐to‐stand time (?24%), and self‐reported health status (+20%) (all P < 0.05). No changes were noted in the CT group (P > 0.05). Protein carbonylation decreased among ET subjects (?27%; P < 0.05), but not in the CT group (P > 0.05). Changes in protein carbonylation were associated with changes in muscle size and pennation angle (r = ?0.44 to ?0.57), exercise capacity (r = ?0.46), muscle strength (r = ?0.45), and sit‐to‐stand performance (r = 0.60) (all P < 0.05). The combination of HIIT and power training improved systemic oxidative stress and limb muscle dysfunction in older people with COPD. Changes in oxidative stress were associated with exercise‐induced structural and functional adaptations.     

Using surface electrodes for the evaluation of the rectus femoris, vastus medialis and vastus lateralis muscles in children with cerebral palsy

The purpose of this study was to determine if surface electrodes are adequate in the determination of the activity patterns of the rectus femoris, vastus medialis and vastus lateralis in children with cerebral palsy (CP). Ninety patients with a diagnosis of CP underwent electromyography (EMG) testing. Surface electrodes were placed on the rectus femoris (RF), hamstrings, vastus medialis (VM) and vastus lateralis (VL). Muscle isolation tests revealed no cross-talk of the RF muscle on the vastii electrodes in any subject indicating surface EMG is sufficient for testing RF, VM and VL function in children. Muscle activation patterns during gait showed that the RF and not the VM or VL was active in mid-swing in the majority of cases.     

Voluntary and electromyostimulation forces in trained and untrained men.

Electromyostimulation (EMS) evoked responses of lower extremity muscles of sedentary or disabled subjects have been extensively studied to improve muscular strength and delay atrophy. However, it is not apparent whether EMS can serve a similar function in upper extremity muscles and in athletes. We compared the forces of maximal voluntary isometric contraction (MVC), percutaneous EMS-evoked tetanus, and EMS superimposed on MVC of the elbow flexors in six strength-trained and six untrained healthy men. Stimulation consisted of a 2.5-kHz alternating current sine wave modulated at 50 bursts.s-1 with a 50% duty cycle. Reliability of the criterion measures was assessed over 4 d and ranged from R = 0.746 to R = 0.948. Strength-trained men had 29% higher MVC than untrained controls (P less than 0.001). Untrained men tolerated 21.9 mA and trained men 31.3 mA of EMS current (P less than 0.021), yet tetanic forces were similar: 92.5 N vs 96.0 N (P greater than 0.196). These tetanic forces corresponded to 32% (untrained) and 24% (trained) of MVC (P less than 0.047). When EMS was superimposed on MVC, compared with MVC alone, force was significantly (P less than 0.048) lower by 10% (31 N, untrained) and 13% (55 N, trained). These data suggest that, independent of training status, percutaneous EMS reduces maximal voluntary elbow flexion forces and that tetanic forces may not be sufficiently high for purposes of muscular strength development or prevention of atrophy.     

Combined effects of whole-body vibration, resistance exercise, and vascular occlusion on skeletal muscle and performance

The purpose of this study was to evaluate the effects of a new high-intensity training modality comprised of vibration exercise with superimposed resistance exercise and vascular occlusion (vibroX) on skeletal muscle and performance. Young untrained women were randomized to either train in a progressive mode on 3 days per week for 5 weeks ( N=12) or to maintain a sedentary lifestyle ( N=9). VibroX increased peak cycling power (+9%, P=0.001), endurance capacity (+57%, P=0.002), ventilatory threshold (+12%, P<0.001), and end-test torque (+15%, P=0.002) relative to the sedentary group. Training load increased by 84.5% ( P<0.001) after vibroX. The increases were paralleled by increases in myosin heavy chain type 1 vastus lateralis muscle fiber cross-sectional area (+14%, P=0.031) and proportion (+17%, P=0.015), thigh lean mass (+4%, P=0.001), capillary-to-fiber ratio (+14%, P=0.003), and cytochrome c oxidase activity. Conversely, maximal values for oxygen consumption, cardiac output, isokinetic leg extension power and jumping power remained unaffected. Notably, vastus lateralis muscle adaptations were achieved with a very low weekly training volume. We conclude that vibroX quickly increases muscle (fiber) size, capillarization, and oxidative potential, and markedly augments endurance capacity in young women.     

Electromyostimulation and plyometric training effects on jumping and sprint time

This study compared the effects of four-week training periods of electromyostimulation (EMS), plyometric training (P), or combined EMS and P training of the knee extensor muscles on 20 m sprint time (ST), jumping ability (Squat jump [SJ] and Countermovement jump [CMJ]), maximal isometric strength (MVC), and muscle cross-sectional area (CSA). Forty subjects were randomly assigned to one of the four treatment groups: electromyostimulation (EG), plyometric (PG), combined EMG, and P (EPG), that took place 4 times per week, and a control group (CG). Subjects were tested before and after the training program, as well as once more after 2 wk of detraining. A significant improvement (p < 0.05) in ST was observed after training (2.4 %) in EG while a significant slowing (p < 0.05) was observed (- 2.3 %) in EPG. Significant increases in EPG (p < 0.05) were observed in SJ (7.5 %) and CMJ (7.3 %) after training, while no significant changes in both jumps were observed after training and detraining for EG. A significant increase (p < 0.05) in MVC was observed after training (9.1 %) and after detraining (8.1 %) in EG. A significant increase (p < 0.05) in MVC was observed after training (16.3 %) in EPG. A significant increase (p < 0.01) in CSA was observed after training in EG (9.0 %) and in EPG (7.1 %). EMS combined with plyometric training increased the jumping height and sprint run in physically active men. In addition, EMS alone or EMS combined with plyometric training leads to increase maximal strength and to some hypertrophy of trained muscles. However, EMS training alone did not result in any improvement in jumping explosive strength development or even interfered in sprint run.