Resistance training during unweighting maintains muscle size and function in human calf

PURPOSE: A 20-d 6 degrees head-down tilt bed rest project was conducted to evaluate the effect of dynamic leg press and plantar flexion resistance training on muscle size and function in human plantar flexors (PF) throughout the prolonged bed rest. METHODS: Twelve healthy men participated in this study and were divided two groups: resistance training (BR-Tr group: N = 6, age: 23 +/- 2 yr, height: 170 +/- 3 cm, weight: 66 +/- 7 kg) and nontraining (BR-Cont group: N = 6, age: 23 +/- 1 yr, height: 170 +/- 3 cm, weight: 67 +/- 6 kg) during the bed rest. Physiological cross-sectional area (PCSA) and peak torque of the PF muscle group was determined. Spin-spin relaxation times (T2) of the medial (MG) and lateral gastrocnemius (LG) and soleus (Sol) muscle was measured at rest and immediately after unilateral calf-raising exercise (5 sets of 10 reps). RESULTS: PCSA of the PF muscle group did not show any significant change in BR-Tr group; however, for the BR-Cont group, PCSA decreased by 13% after bed rest (P < 0.05). There was no significant change in exercise-induced T2 change of the MG, LG, or Sol muscles between before and after the bed rest in BR-Tr group; however, in the BR-Cont group, significant increases in T2 were found in these three muscles after the bed rest (P < 0.05 to 0.01). CONCLUSION: We conclude that dynamic leg press and plantar flexion resistance training during bed rest maintains muscle size and function (torque and T2), and that this training could be useful for prevention of progressive muscle deconditioning during spaceflight.     

Effect of arthroscopic partial meniscectomy on the function of quadriceps femoris

The purpose of this study was to investigate the functional characteristics of the quadriceps femoris (QF) muscle group after the effect of presurgery disuse, surgery, and postsurgery disuse using surface electromyography and muscle functional magnetic resonance imaging (mfMRI). A total of 20 individuals (11 men and nine women) who underwent arthroscopic knee surgery participated in this study. Maximum voluntary contraction (MVC) of the QF muscle group was measured in the legs that received surgery and those that did not. To acquire the functional properties of the QF muscle group, electromyographic (EMG) activity during repetitive dynamic knee extension exercises (five sets of ten repetitions; load 30% MVC) and mfMRI before and after the exercises were obtained. EMG activity was evaluated in three phases depending on the knee joint angle: concentric and eccentric phases (Con/Ecc), concentric (Con) phase only, and eccentric (Ecc) phase only. The mean MVC of the legs that received surgery was significantly lower (22%) than that of the legs that did not. Regarding the EMG activity during the Con/Ecc and Con phases, there were significant leg and set effects but no significant leg-by-set interactions; however, during the Ecc phase, there was a significant set effect. Regarding changes in the mfMRI signal, leg and exercise had significant effects, but there was no significant leg-by-exercise interaction. These results suggest that presurgery disuse, partial meniscectomy, and postsurgery disuse induce dysfunction of the QF muscle group that is dependent on a decrease in MVC. Thus, these patients need maximal muscle-force improvement for effective rehabilitation after surgery.     

Acceleration with exercise during head-down bed rest preserves upright exercise responses

INTRODUCTION: This study was designed to elucidate the effect of short-arm centrifuge-induced artificial gravity with exercise training during ground-based simulated spaceflight, i.e., prolonged head-down bed rest (HDBR), on respiratory and cardiovascular responses to upright exercise. METHODS: There were 10 healthy men who underwent 20 d of -6 degrees HDBR, and were assigned to either a countermeasure (CM) group (n = 5) or a no countermeasure (No-CM) group (n = 5). The subjects in the CM group performed two sessions (20 min each session, 40 min total) of short-arm centrifuge-induced artificial gravity with exercise training in a supine position on alternate days (10 d total) during HDBR. The first session was set at 0.8-1.4 G load at heart level with a constant exercise intensity (60 W), and the second session began with a 0.3 G load at heart level with an interval exercise protocol (40-80% peak oxygen uptake; VO2peak). The measurements of respiratory and cardiovascular responses to incremental exercise were performed pre- and post-HDBR. RESULTS: The 20 d of HDBR increased minute expired ventilation, heart rate, and respiratory exchange ratio and decreased stroke volume during submaximal exercise in the No-CM group, whereas these parameters were unchanged in the CM group. In the No-CM group, VO2peak decreased significantly (47.0 +/- 8.6 to 34.8 +/- 6.8 ml x kg(-1) x min(-1), p < 0.05), whereas VO2peak in the CM group did not show a significant decrease following 20 d of HDBR (47.7 +/- 10.0 to 43.9 +/- 8.9 ml x kg(-1) x min(-1)). These results suggest that short-arm centrifuge-induced artificial gravity with exercise training is effective in maintaining respiratory and cardiovascular responses to upright exercise.     

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.     

The effects of ice application over the vastus medialis on the activity of quadriceps femoris assessed by muscle function magnetic resonance imaging

AIM: The purpose of this study was to investigate the effect of ice application for the muscle vastus medialis (VM) on the activation pattern of the quadriceps femoris muscle during repetitive knee extensions using muscle function magnetic resonance imaging (mfMRI) technique. METHODS: Seven men underwent transverse relaxation time (T2)-weighted magnetic resonance imaging (spin echo, TR/TE=1500/25, 80 ms, 10 mm slice thickness and gap) of their right thigh at rest and immediately after isotonic knee extension exercise with 5 sets of 10 repetitions at a load equal to 70% of their 10 repetitions with and without skin cooling. Cooling over surface skin of the VM was carried out for 3 min before and during 60-s of each rest interval between the knee extension exercise. RESULTS: The relative change in T2 of the muscle vastus intermedius increased significantly more by skin cooling than the control (p<0.01), but not the muscle rectus femoris (RF), muscle vastus lateralis, and VM. CONCLUSION: These results suggest that selective skin cooling combined with repeated muscle contraction facilitates the activation of other synergistic muscles, making this technique useful for activating the agonist muscles expected for injured muscle in training and rehabilitation.     

Hamstring functions during hip-extension exercise assessed with electromyography and magnetic resonance imaging

The purpose of this study was to compare the recruitment patterns in hamstring muscles during hip extension exercise by electromyography (EMG) and muscle functional magnetic resonance imaging (mfMRI). Six male volunteers performed 5 sets of 10 repetitions of the hip extension exercise. Electromyography (EMG) activity during the exercise was recorded for the biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles; mfMRI T2 values and cross-sectional areas (CSAs) of the same muscles were measured at rest, immediately after, 2 and 7 days after the exercise. The study found that EMG of the BFlh and SM were significantly higher than that of the ST. Immediately after the exercise, the T2 value and CSA changes in the SM showed a significant increase. It was concluded that the BFlh and SM were selectively recruited during the hip extension exercise.     

Neuromuscular activation of triceps surae using muscle functional MRI and EMG

PURPOSE: The aim of the present study was to clarify the neuromuscular activation patterns among individual triceps surae (TS) muscles during a repetitive plantarflexion using muscle functional magnetic resonance imaging (MRI) (mfMRI) and electromyography (EMG). METHODS: Six healthy men participated in this study, performing 5 sets of 10 repetitions of a calf-raise exercise bilaterally, unilaterally, and unilaterally with an additional 15% of body-weight load. The transverse relaxation times (T2) in the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles were measured from mfMR images obtained with the subject at rest and immediately after exercise; integrated EMG (iEMG) activity was recorded from the same muscles during exercise using surface electrodes. RESULTS: There was remarkable correspondence between the changes in T2 values and iEMG activity under the three different workloads for individual TS muscles. In addition, changes in T2 value that occurred as a function of increasing exercise loads were linearly correlated with iEMG activity in the MG (r=0.58, P<0.05) and SOL (r=0.63, P<0.01), but not in the LG. CONCLUSIONS: These results suggest that 1) mfMRI signals and iEMG activity correlate with workload in individual TS muscles, 2) mfMRI signals are associated with neuromuscular activity reflected in iEMG in the MG and SOL but not in the LG, and 3) these relationships are associated with neuromuscular and metabolic factors during exercise.     

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.     

The relationship between isokinetic knee extension and flexion strength with soccer kick kinematics: an electromyographic evaluation

AIM: The purpose of this study was to investigate the relationship between isokinetic strength knee testing and soccer kick kinematics using electromyography (EMG). METHODS: Thirteen pubertal soccer players (age: 14.3+/-0.4 years) performed maximum instep soccer kicks, while knee angular position of the swinging leg was recorded using a twin-axis electrogoniometer. Bipolar surface EMG activity of the vastus medialis, vastus lateralis and biceps femoris (BF) muscles was recorded. The subjects also performed maximum knee extension and flexion efforts at concentric angular velocities of 1.04, 3.14 and 5.23 rad x s(-1) and eccentric angular velocities of 1.04 and 3.14 rad x s(-1). RESULTS: The correlation coefficients between isokinetic moments and knee angular velocity values during the kick ranged from 0.609 to 0.898 for concentric moments and from 0.431 to 0.612 for eccentric moments. Agonist EMG values during isokinetic tests ranged from 63.17+/-19.9% to 128.7+/-34.9% maximum voluntary contraction (MVC). Antagonist EMG levels ranged from 9.76+/-6.12% to 36.91+/-22.81% MVC. The corresponding EMG values during the soccer kick ranged from 12.78+/-6.8% to 122.34+/-61.5% MVC and increased as the foot approached the ball. CONCLUSION: Isokinetic tests at intermediate and fast angular velocities are adequate for monitoring strength training programs in soccer. However, muscle activation patterns differ between the two movements, especially those of the BF muscle.     

Electromyostimulation training effects on neural drive and muscle architecture

PURPOSE: The purpose of the study was to investigate the effect of 4 and 8 wk of electromyostimulation (EMS) training on both muscular and neural adaptations of the knee extensor muscles. METHODS: Twenty males were divided into the electrostimulated group (EG, N = 12) and the control group (CG, N = 8). The training program consisted of 32 sessions of isometric EMS over an 8-wk period. All subjects were tested at baseline (B) and retested after 4 (WK4) and 8 (WK8) wk of EMS training. The EMG activity and muscle activation obtained under maximal voluntary contractions (MVC) was used to assess neural adaptations. Torque and EMG responses obtained under electrically evoked contractions, muscle anatomical cross-sectional area (ACSA), and vastus lateralis (VL) pennation angle, both measured by ultrasonography imaging, were examined to analyze muscular changes. RESULTS: At WK8, knee extensor MVC significantly increased by 27% (P < 0.001) and was accompanied by an increase in muscle activation (+6%, P < 0.01), quadriceps muscle ACSA (+6%, P < 0.001), and VL pennation angle (+14%, P < 0.001). A significant increase in normalized EMG activity of both VL and vastus medialis (VM) muscles (+69 and +39%, respectively, P < 0.001) but not of rectus femoris (RF) muscle was also found at WK8. The ACSA of the VL, VM, and vastus intermedius muscles significantly increased at WK8 (5-8%, P < 0.001) but not at WK4, whereas no changes occurred in the RF muscle. CONCLUSION: We concluded that the voluntary torque gains obtained after EMS training could be attributed to both muscular and neural adaptations. Both changes selectively involved the monoarticular vastii muscles.     

Electromyographic (EMG) normalization method for cycle fatigue protocols

PURPOSE: To determine the most effective electromyographic (EMG) normalization method for cycling fatigue protocols. METHODS: Ten healthy subjects performed two 5-s isometric knee extension maximal voluntary contractions (MVC) at a knee joint angle of 60 degrees, two fixed cycle pedal contraction at knee joint angles of 60 degrees (60 degrees A) and 108 degrees (108 degrees A), and a dynamic single maximal revolution of a cycle pedal (1REV). Integrated EMG (IEMG) data were recorded for all contractions and power output recorded during MVC and 1REV. RESULTS: Mean IEMG for MVC was significantly (P < 0.01) greater than 60 degrees C, 108 degrees C, and 1REV. There were no significant differences between MVC and 1REV power output/EMG relationship. CONCLUSIONS: MVC will record a higher IEMG than 60 degrees A, 108 degrees A, and 1REV. As IEMG was greatest during MVC, and the relationship between IEMG and power output was not different between MVC and 1REV, normalization against maximal possible recruitment potential is most likely during MVC.     

EMG power spectra of intercollegiate athletes and anterior cruciate ligament injury risk in females

PURPOSE: Females have a disproportionately high incidence of anterior cruciate ligament (ACL) injuries compared with males in analogous sports. Although the pathogenesis of this higher frequency has not been elucidated, gender differences in neuromuscular control of the knee may play an important role. This study evaluates EMG power spectra of the quadriceps and hamstring muscles during dynamic, fatiguing exercise to examine differences between male and female intercollegiate athletes. METHODS: Fifty-one collegiate basketball and soccer players (25 female, 26 male) were studied. Maximum voluntary contraction (MVC) was determined for knee flexion and extension. Three consecutive 2-min bouts of isokinetic knee flexion and extension exercise were performed at 40% MVC. EMG activity in the biceps femoris and vastus medialis obliquus was recorded using bipolar surface electrodes. RESULTS: MVC normalized to body weight was significantly greater in males than in females for the quadriceps (P< 0.01). Quadriceps coactivation ratios were significantly higher in females than in males during knee flexion exercises (P< 0.01). CONCLUSIONS: This study demonstrates differences in the EMG power spectra for females when compared with a matched group of males. Increased quadriceps coactivation in females may increase anterior tibial loads under dynamic conditions, thus placing the ACL at higher risk for injury in the female athlete.     

Recruitment of the thigh muscles during sprint cycling by muscle functional magnetic resonance imaging

The purpose of the present study was to investigate recruitment patterns of the thigh muscles during maximal sprint cycling by muscle functional magnetic resonance imaging (mfMRI). Twelve healthy men participated in this study and performed 2, 5, and 10 sets of 6-s supramaximal cycling with a load of 7.5 % of their body weight with 0.5 min of rest between the sets. Before and immediately after the exercise, T2-weighted MR images, i.e. mfMRI, of the right-thigh were taken to calculate T2 of eleven thigh muscles. Vastus lateralis, semitendinosus, and sartorius were the highest activated, i. e. had the greatest T2 change, among the quadriceps, hamstring, and adductors, respectively, compared with other muscles. Total power output during 2, 5, and 10 sets of sprint cycling was correlated with percent change in T2 in the quadriceps correlated (r (2) = 0.507 to 0.696, p < 0.01), the hamstring (r (2) = 0.162 to 0.335, p < 0.05 approximately 0.001), and the adductor muscles (r (2) = 0.162 to 0.473, p < 0.05 approximately 0.0001). With use of stepwise regression analysis, total power output was significantly correlated with % change in T2 of the vastus medialis (VM) (p < 0.0001) and vastus intermedius (VI) (p < 0.05) (r (2) = 0.698, p < 0.0001). We concluded that eleven thigh muscles were activated non-uniformly, and that the VM and VI play a key role during maximal sprint cycling.     

Comparison of two abdominal training devices with an abdominal crunch using strength and EMG measurements

BACKGROUND: The purpose of this study was to compare the training effects of the Ab-Flex (F), Ab-Roller (R) and standard crunch (C) on EMG production, isometric maximum voluntary contraction (MVC), and isokinetic average peak torque at 30 degrees/sec (ISO) of the abdominal muscles. It was hypothesized that the training devices would have similar value in a strength training program. METHODS: Experimental design: this was a prospective study involving 18 training sessions of progressively increasing repetitions. Setting: Neuromuscular Research Laboratory, University of Pittsburgh. Subjects: thirty-two subjects volunteered for this study, but only 26 completed the training. Each subject participated in recreational activity, but had not performed any abdominal training prior to starting this study. Each subject was randomly assigned to either the control group or one of the treatment groups. Interventions: there were three interventions: two training devices (Ab-Flex and Ab-Roller) and the standard crunch, considered a control group. Measures: the pretest consisted of skin fold measurements (%), EMG activity (V) during the three interventions, and peak torque (Nm) plus EMG during the MVC and ISO tasks. The 18 training sessions over three weeks consisted of three sets of exercise with increasing repetitions from 10 to 20, by 2, every three sessions. The difference in pretest/posttest scores were compared using a One-way ANOVA on the mean differences (Mdiff) for each of: MVC, ISO (peak torque), and EMG for upper rectus (UR), lower rectus (LR), internal oblique (IO), and external oblique (EO). A T-Test was used to detect significance for the body fat measures. RESULTS: Mean differences (Mdiff) were normally distributed about zero for both MVC and ISO (MVC = -0.55, ISO = 4.57). The analysis by group showed no difference (p = 0.596) on the reported means (Nm) -3.16 (C), 5.84 (F) and -4.83 (R). The change associated to the treatment during MVC was only 4% (eta = 0.04). For the ISO the Mdiff (Nm) were 1.39 (C), 13.66 (F) and -2.06 (R) which were not significant (p = 0.127). The Ab-Flex was the only group to have a 95% confidence interval above zero, increasing by an average of 16.5%. There were no significant differences for the EMG activity for Mdiff or between group scores. CONCLUSIONS: No significant differences were found with this study. These results would suggest that using these devices does not add significantly to overall abdominal strength development, or reduction of body fat. A suggestion could be made that certain devices influence muscles differently.     

Facilitation of quadriceps activation is impaired following eccentric exercise

Contracting the knee flexor muscles immediately before a maximum voluntary contraction (MVC) of knee extension increases the maximal force that the extensor muscles can exert. It is hypothesized that this phenomenon can be impaired by muscle fiber damage following eccentric exercise [delayed onset muscle soreness (DOMS)]. This study investigates the effect of eccentric exercise and DOMS on knee extension MVC immediately following a reciprocal‐resisted knee flexion contraction. Electromyography (EMG) was recorded from the knee extensors and flexors of 12 healthy men during knee extension MVCs performed in a reciprocal (maximal knee extension preceded by resisted knee flexion), and nonreciprocal condition (preceded by relaxation of the knee flexors). At baseline, knee extension MVC force was greater during the reciprocal condition (P < 0.001), whereas immediately after, 24 and 48 h after eccentric exercise, the MVC force was not different between conditions. Similarly, at baseline, the EMG amplitude of the quadriceps during the MVC was larger for the reciprocal condition (P < 0.001). However, immediately after, 24 and 48 h postexercise the EMG amplitude was similar between conditions. In conclusion, eccentric exercise abolished the facilitation of force production for the knee extensors, which normally occurs when maximum knee extension is preceded by activation of the knee flexors.     

Quadriceps femoris torque and EMG activity in seated versus supine position

PURPOSE: To compare voluntary and electrically evoked knee extensor torque, surface electromyography (EMG), and activation level obtained under seated versus supine position, i.e., with shortened versus lengthened rectus femoris (RF) muscle. METHODS: The knee extensor torque obtained during maximal voluntary contractions (MVC) and after single and paired stimuli applied at rest was measured under seated (i.e., 90 degrees hip angle) and supine (i.e., 180 degrees hip angle) conditions. The associated EMG activity from biarticular RF and monoarticular vasti was also recorded, and activation level was estimated by means of the twitch interpolation technique. RESULTS: Knee extensor MVC was 10.6% higher in the seated compared with the supine position (P < 0.01). EMG normalized to the M-wave amplitude for respective muscles and for respective positions was significantly lower under supine conditions, and deficits averaged approximately 20% for vasti and approximately 41% for RF (P < 0.05). Similarly, activation level estimated in the supine position was approximately 4% lower than the seated counterpart. Relative MVC losses observed supinely were significantly correlated with the corresponding activation level deficits (P < 0.05). On the other hand, both single and paired stimuli resulted in higher torque amplitudes in the supine with respect to the seated position, and mean differences were comprised between 10% (single twitch, P < 0.05) and 20% (potentiated doublet, P < 0.001). RF M-wave amplitude recorded supinely was 19% higher than the seated counterpart (P < 0.01). CONCLUSION: The higher neural activation observed for the knee extensor muscles in the seated versus supine position, likely attributable to improved motor unit recruitment, may reflect a neurophysiological mechanism partly compensating the neuromuscular transmission-propagation impairment and/or mechanical disadvantage of shortened RF muscle.     

Strength training and neuromuscular function in elderly people with total knee endoprosthesis

The effects of 1 year of intensive strength training on neuromuscular function were studied in elderly people operated for total endoprosthesis ( n =30) divided into 3 groups: training pup 1 (TG1, n =11), training pup 2 (TG2, n =10) and control group (CG, n =9). After the operation, TG1 and TG2 trained every second day and the training was controlled by training diaries, and CG performed only conventional exercises by themselves. The overall volume of training in TG2 was 30% greater than in TG1. Neuromuscular function was examined by measuring maximal electromyography (EMG) and maximum voluntary isometric and dynamic strength of the knee extensor and flexor muscles. The range of motion of the knee joint and the cross-sectional area (CSA) of the knee extensor muscles were also measured. After the preoperative tests, the same measurements were repeated 3, 6, 12, 24 and 52 weeks postoperatively. After the dramatic decreases in maximal isometric torque and EMG-activity during the first postoperative weeks in all groups, TG2 showed the most remarkable improvement in neuromuscular function. For instance, the maximum isometric extension torque measured at 90° knee angle increased between the 24th and 52nd weeks. The increase in the EMG-activity of the rectus femoris muscle was Significant between the 12th and 24th weeks. The CEA of the knee extensor muscles in TG2 was greater 1 year after the operation compared with the preoperative value. The intra- and extra-articular swelling of the knee joint may have irritated the free nerve endings, leading to reflex inhibition with a concomitant decrease in EMG and strength of the knee extensor muscles. Because TG2 demonstrated the most remarkable improvement in neuromuscular function after the first postoperative weeks, intensive training programs can be successfully used in rehabilitation after a major knee operation, even in elderly people.     

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。     

Steadiness training with light loads in the knee extensors of elderly adults

PURPOSE: This study was conducted to determine the effect of steadiness training with light loads in the knee extensors of elderly adults. METHODS: Twenty-one elderly adults (72 +/- 4.6 yr) performed 16 wk of closely supervised knee extensor training that consisted of lifting and lowering 30% of the one-repetition maximum (1-RM) load as steadily as possible (10 reps per set, three sets per session, three sessions per week). Nine subjects served in a control group. Unilateral and bilateral maximal voluntary contraction (MVC) force; 1-RM load; force fluctuations during submaximal isometric, concentric, and eccentric contractions; timed functional performance (gait, chair rise, stair ascent and descent); muscle volume via magnetic resonance imaging (MRI); and the electromyogram (EMG) were measured. RESULTS: The training group exhibited modest average gains in MVC force and 1-RM load; muscle volume and EMG were unaltered. Although isometric steadiness was unchanged on average, training elicited the greatest improvements in the least steady subjects. Force fluctuations during concentric and eccentric contractions were significantly reduced. Of 21 subjects, 14 responded to training with gains in 1-RM load greater than the typical change (6%) in the control group. Before training, these responders exhibited greater force during bilateral compared with unilateral contractions. The small changes in physical functional performance were similar for the training and control groups. The training group could lift the pretraining 1-RM load 4.6 times after training (5.6 times for responders). CONCLUSIONS: Steadiness training with the knee extensors thus produced neural adaptations that increased strength in elderly adults who exhibited bilateral facilitation, improved isometric steadiness in unsteady subjects, improved steadiness during concentric and eccentric contractions, and enhanced the ability to lift heavy loads repeatedly.     

Does fatigue induced by repeated dynamic efforts affect hamstring muscle function?

PURPOSE: The purpose of this study was to determine the effects of hamstring fatigue induced by repeated maximal efforts on hamstring muscle function during maximal sprint running. METHODS: Twelve subjects performed three maximal 40-m sprints during which time high-speed film of the subjects' sprint action and EMG of five lower extremity muscles were recorded (nonfatigued condition, NFC). Subjects then performed specific and general hamstring fatigue tasks followed by three final 40-m sprints (fatigued condition, FC) during which time high-speed film and EMG of the same muscles were again recorded. RESULTS: Statistical analysis of the kinematic data indicated the following significant (P < 0.05) changes in the subjects' running action from the NFC to the FC: decreased hip and knee flexion at maximum knee extension in the swing phase of the sprint cycle, decreased leg angular velocity immediately before foot-ground contact (FGC), and decreased angular displacement of the trunk, thigh, and leg segments during the late swing phase. Statistical analysis of the EMG data indicated a significant increase in the duration of hamstring activity and earlier cessation of rectus femoris activity during the swing phase of the sprint stride. CONCLUSIONS: It was concluded that these changes in the kinematic and EMG parameters of sprint running primarily served as protective mechanisms to reduce stress placed on the hamstring muscles at critical phases of the stride cycle.