Training-induced changes in neuromuscular performance under voluntary and reflex conditions

To investigate training-induced changes in neuromuscular performance under voluntary and reflex contractions, 11 male subjects went through heavy resistance (high loads of 70-120% of one maximum repetition) and 10 male subjects through explosive type (low loads with high contraction velocities) strength training three times a week for 24 weeks. A large increase (13.9%, p less than 0.01) in voluntary unilateral maximal knee extension strength with only slight and insignificant changes in time of isometric force production were observed during heavy resistance strength training. Explosive type strength training resulted in a small insignificant increase in maximal strength but in considerable shortening (p less than 0.05) in the time of force production. A significant increase (p less than 0.05) noted in the averaged maximal integrated electromyogram (IEMG) of the knee extensors during heavy resistance strength training correlated (p less than 0.01) with the increase in maximal strength. No changes were noted during training in reflex time components, but significant decreases (p less than 0.05) occurred in the peak-to-peak amplitudes of the reflex electromyograms (EMG) in both groups. The individual changes during training in the reflex EMG/force ratio were related (p less than 0.01) to the respective changes in IEMG/force ratio in voluntary contractions. The present observations support the concept of specificity of training, and suggest that specific training-induced adaptations in the neuromuscular system may be responsible for these changes in performance.     

High resistance/low repetition vs. low resistance/high repetition training: effects on performance of trained cyclists

In order to investigate the effects of a resistance training modality on cycling performance, 23 trained club-level cyclists were placed into high resistance/low repetition (H-Res), low resistance/high repetition (H-Rep), or cycling-only groups for a 10-week program. All 3 groups followed the same cycling plan, but the H-Res and H-Rep groups added resistance training. Testing pre and post consisted of a graded incremental lactate profile test on an ergometer, with blood lactate being sampled. VO2 values were measured to determine economy. Maximum strength testing of 4 strength exercises targeting the lower extremity musculature was conducted with the H-Res and H-Rep groups. There were significant gains in all 4 resistance training exercises (p < 0.05) for both H-Res and H-Rep, with the H-Res group having significantly greater gains than the H-Rep group had in the leg press exercise (p < 0.05). There were, however, no significant group x training differences (p > 0.05) found between the 3 training groups on the cycling test in lactate values or economy. It appears that for this population of cyclists, neither H-Res nor H-Rep resistance training provided any additional performance benefit in a graded incremental cycling test when compared with cycling alone over a training time of this length. It is possible that with this population, various factors such as acute fatigue, strength, and aerobic gains from the cycling training, in addition to well-developed bases of strength and conditioning from previous training, reduced differences between groups in both strength gains and cycling performance.     

Effects of Blood Flow Restricted Low-Intensity Concentric or Eccentric Training on Muscle Size and Strength

We investigated the acute and chronic effects of low-intensity concentric or eccentric resistance training with blood flow restriction (BFR) on muscle size and strength. Ten young men performed 30% of concentric one repetition maximal dumbbell curl exercise (four sets, total 75 reps) 3 days/week for 6 weeks. One arm was randomly chosen for concentric BFR (CON-BFR) exercise only and the other arm performed eccentric BFR (ECC-BFR) exercise only at the same exercise load. During the exercise session, iEMG for biceps brachii muscles increased progressively during CON-BFR, which was greater (p<0.05) than that of the ECC-BFR. Immediately after the exercise, muscle thickness (MTH) of the elbow flexors acutely increased (p<0.01) with both CON-BFR and ECC-BFR, but was greater with CON-BFR (11.7%) (p<0.01) than ECC-BFR (3.9%) at 10-cm above the elbow joint. Following 6-weeks of training, MRI-measured muscle cross-sectional area (CSA) at 10-cm position and mid-upper arm (12.0% and 10.6%, respectively) as well as muscle volume (12.5%) of the elbow flexors were increased (p<0.01) with CON-BFR. Increases in muscle CSA and volume were lower in ECC-BFR (5.1%, 0.8% and 2.9%, respectively) than in the CON-BFR and only muscle CSA at 10-cm position increased significantly (p<0.05) after the training. Maximal voluntary isometric strength of elbow flexors was increased (p<0.05) in CON-BFR (8.6%), but not in ECC (3.8%). These results suggest that CON-BFR training leads to pronounced acute changes in muscle size, an index of muscle cell swelling, the response to which may be an important factor for promoting muscle hypertrophy with BFR resistance training.     

Effects of resistance training on the physical capacities of adolescent soccer players

This study examined the effects of a progressive resistance training program in addition to soccer training on the physical capacities of male adolescents. Eighteen soccer players (age: 12-15 years) were separated in a soccer (SOC; n = 9) and a strength-soccer (STR; n = 9) training group and 8 subjects of similar age constituted a control group. All players followed a soccer training program 5 times a week for the development of technical and tactical skills. In addition, the STR group followed a strength training program twice a week for 16 weeks. The program included 10 exercises, and at each exercise, 2-3 sets of 8-15 repetitions with a load 55-80% of 1 repetition maximum (1RM). Maximum strength ([1RM] leg press, bench-press), jumping ability (squat jump [SJ], countermovement jump [CMJ], repeated jumps for 30 seconds) running speed (30 m, 10 x 5-m shuttle run), flexibility (seat and reach), and soccer technique were measured at the beginning, after 8 weeks, and at the end of the training period. After 16 weeks of training, 1RM leg press, 10 x 5-m shuttle run speed, and performance in soccer technique were higher (p < 0.05) for the STR and the SOC groups than for the control group. One repetition maximum bench press and leg press, SJ and CMJ height, and 30-m speed were higher (p < 0.05) for the STR group compared with SOC and control groups. The above data show that soccer training alone improves more than normal growth maximum strength of the lower limps and agility. The addition of resistance training, however, improves more maximal strength of the upper and the lower body, vertical jump height, and 30-m speed. Thus, the combination of soccer and resistance training could be used for an overall development of the physical capacities of young boys.     

The effects of accentuated eccentric loading on strength, muscle hypertrophy, and neural adaptations in trained individuals

The purpose of this study was to compare the strength and neuromuscular adaptations for dynamic constant external resistance (DCER) training and dynamic accentuated external resistance (DAER) training (resistance training employing an accentuated load during eccentric actions). Male subjects active in resistance training were assigned to either a DCER training group (n = 10) or a DAER training group (n = 8) for 9 weeks. Subjects in the DCER group performed 4 sets of 10 repetitions with a load of 75% concentric 1 repetition maximum (RM). Subjects in the DAER group performed 3 sets of 10 repetitions with a concentric load of 75% of 1RM and an eccentric load of approximately 120% of concentric 1RM. Three measures reflecting adaptation of elbow flexors and extensors were recorded pretraining and posttraining: concentric 1RM, muscle cross-sectional area (CSA), and specific tension. Strength was assessed at midtraining periods. No significant changes in muscle CSA were observed in either group. Both training groups experienced significant increases in concentric 1RM and specific tension of both the elbow flexors and extensors, but compared with DCER training, DAER training produced significantly greater increases in concentric 1RM of the elbow extensors. These results suggest that, for some exercises, DAER training may be more effective than DCER training in developing strength within a 9-week training phase. However, for trained subjects, neither protocol is effective in eliciting muscle hypertrophy.     

Strength outcomes in fixed versus free-form resistance equipment

The purpose of this study was to compare measures of strength and balance between subjects using fixed form or free-form resistance training equipment to determine whether there is a difference in strength or balance outcomes. Thirty previously untrained subjects, mean age = 49 (+/-3.7 years), were randomly placed in either a free-form strength group (FF n = 10) utilizing a commercially available free-form plate loaded resistance device, a fixed form strength group (FX n = 10) utilizing a commercially available fixed range selectorized resistance device or a control group (C; n = 10) who did not exercise. All groups were assessed during a pretest (T1) and a posttest (T2). The exercise groups were asked to exercise over a 16-week period, increasing resistance based on a standardized 8-12 repetition protocol. The same muscles were targeted in both exercise groups, all groups were instructed not to change their dietary habits. A one-way ANOVA was used to detect differences among the groups using baseline and end results data. FX group increased strength 57% from baseline while the FF group increased strength 115% from baseline. A statistically significant difference (P = 0.000001) was detected for strength production in the FF over the FX group and (P = 0.0000144) over the training and control groups. Balance improved 49% in the FX versus 245% in the FF groups. Testing revealed a statistically significant difference (P < or = 0.003). The control (C) group did not show significant improvement in either strength or balance. Results of this study indicate a greater improvement in FF over FX in strength (58%), and balance (196%). Additionally, the FX reported increased pain levels while the FF group reported lowered overall pain levels.     

Effects of whole-body low-intensity resistance training with slow movement and tonic force generation on muscular size and strength in young men

Our previous study showed that relatively low-intensity (approximately 50% one-repetition maximum [1RM]) resistance training (knee extension) with slow movement and tonic force generation (LST) caused as significant an increase in muscular size and strength as high-intensity (approximately 80% 1RM) resistance training with normal speed (HN). However, that study examined only local effects of one type of exercise (knee extension) on knee extensor muscles. The present study was performed to examine whether a whole-body LST resistance training regimen is as effective on muscular hypertrophy and strength gain as HN resistance training. Thirty-six healthy young men without experience of regular resistance training were assigned into three groups (each n = 12) and performed whole-body resistance training regimens comprising five types of exercise (vertical squat, chest press, latissimus dorsi pull-down, abdominal bend, and back extension: three sets each) with LST (approximately 55-60% 1RM, 3 seconds for eccentric and concentric actions, and no relaxing phase); HN (approximately 80-90% 1RM, 1 second for concentric and eccentric actions, 1 second for relaxing); and a sedentary control group (CON). The mean repetition maximum was eight-repetition maximum in LST and HN. The training session was performed twice a week for 13 weeks. The LST training caused significant (p < 0.05) increases in whole-body muscle thickness (6.8 +/- 3.4% in a sum of six sites) and 1RM strength (33.0 +/- 8.8% in a sum of five exercises) comparable with those induced by HN training (9.1 +/- 4.2%, 41.2 +/- 7.6% in each measurement item). There were no such changes in the CON group. The results suggest that a whole-body LST resistance training regimen is as effective for muscular hypertrophy and strength gain as HN resistance training.     

Effects of unilateral isometric strength training on joint angle specificity and cross-training

The purpose of this study was to examine the effects of unilateral isometric leg extension strength training on the strength and integrated electromyogram (IEMG) of both the trained and untrained limbs at multiple joint angles. A training (TRN) group [nine women; mean (SD) age, 20(1) years] exercised for 6 weeks with isometric leg extensions at 80% of maximal isometric torque. A control (CTL) group [eight women; 21(1) years] did not exercise. The training was performed three times per week on a Cybex II isokinetic dynamometer at a joint angle where the lever arm was 0.79 rad below the horizontal plane. The subjects were tested pre- and posttraining for maximal unilateral isometric torque in both limbs at joint angles of zero, 0.26, 0.79,1.31, and 1.57 rad below the horizontal plane. Bipolar surface electrodes were used to record the IEMG of the vastus lateralis (VL) and vastus medialis (VM) during the isometric tests. Three univariate (torque, IEMG-VL, and IEMG-VM) four-way (group x time x limb x angle) mixed factorial ANOVAs were used to analyze the data. The results indicated joint angle specificity for isometric torque in the TRN group only, with significant increases in torque at 0.79 (P = 0.0004) and 1.31 (P = 0.0039) rad. No significant increases in torque were found in the untrained limb of the TRN group or in either limb of the CTL group. Similarly, there were no significant changes in IEMG as a result of the training for the VL or VM. The joint-angle-specific strength increases without concomitant increases in IEMG were hypothesized to result from joint-angle-specific decreases in antagonistic co-contraction and/or preferential hypertropy of the quadriceps femoris at specific levels of the muscle group.     

Increased number of forced repetitions does not enhance strength development with resistance training

Some research suggests that strength improvements are greater when resistance training continues to the point at which the individual cannot perform additional repetitions (i.e., repetition failure). Performing additional forced repetitions after the point of repetition failure and thus further increasing the set volume is a common resistance training practice. However, whether short-term use of this practice increases the magnitude of strength development with resistance training is unknown and was investigated here. Twelve basketball and 10 volleyball players trained 3 sessions per week for 6 weeks, completing either 4 x 6, 8 x 3, or 12 x 3 (sets x repetitions) of bench press per training session. Compared with the 8 x 3 group, the 4 x 6 protocol involved a longer work interval and the 12 x 3 protocol involved higher training volume, so each group was purposefully designed to elicit a different number of forced repetitions per training session. Subjects were tested on 3- and 6-repetition maximum (RM) bench press (81.5 +/- 9.8 and 75.9 +/- 9.0 kg, respectively, mean +/- SD), and 40-kg Smith Machine bench press throw power (589 +/- 100 W). The 4 x 6 and 12 x 3 groups had more forced repetitions per session (p < 0.01) than did the 8 x 3 group (4.1 +/- 2.6, 3.1 +/- 3.5, and 1.2 +/- 1.8 repetitions, respectively), whereas the 12 x 3 group performed approximately 40% greater work and had 30% greater concentric time. As expected, all groups improved 3RM (4.5 kg, 95% confidence limits, 3.1- 6.0), 6RM (4.7 kg, 3.1-6.3), bench press throw peak power (57 W, 22-92), and mean power (23 W, 4-42) (all p < or = 0.02). There were no significant differences in strength or power gains between groups. In conclusion, when repetition failure was reached, neither additional forced repetitions nor additional set volume further improved the magnitude of strength gains. This finding questions the efficacy of adding additional volume by use of forced repetitions in young athletes with moderate strength training experience.     

Effect of vibration during fatiguing resistance exercise on subsequent muscle activity during maximal voluntary isometric contractions

This investigation was designed to determine if vibration during fatiguing resistance exercise would alter associated patterns of muscle activity. A cross-over design was employed with 8 subjects completing a resistance exercise bout once with a vibrating dumbbell (V) (44 Hz, 3 mm displacement) and once without vibration (NV). For both exercise bouts, 10 sets were performed with a load that induced concentric muscle failure during the 10th repetition. The appropriate load for each set was determined during a pretest. Each testing session was separated by 1 week. Electromyography (EMG) was obtained from the biceps brachii muscle at 12 different time points during a maximum voluntary contraction (MVC) at a 170 degrees elbow angle after each set of the dumbbell exercise. The time points were as follows: pre (5 minutes before the resistance exercise bout), T1-T10 (immediately following each set of resistance exercise), and post (15 minutes after the resistance exercise bout). EMG was analyzed for median power frequency (MPF) and maximum (mEMG). NV resulted in a significant decrease in MPF at T1-T4 (p < or 0.05) and a significant increase in mEMG at T2 during the MVC. V had an overall trend of lower mEMG in comparison to NV. The mEMG and MPF values associated with NV were similar to previously reported investigations. The lower mEMG values and the higher MPF of V in comparison to NV are undocumented. The EMG patterns observed with vibration may indicate a more efficient and effective recruitment of high threshold motor units during fatiguing contractions. This may indicate the usage of vibration with resistance exercise as an effective tool for strength training athletes.     

Early-phase neuroendocrine responses and strength adaptations following eccentric-enhanced resistance training

The purpose of this study was to evaluate the early-phase muscular performance adaptations to 5 weeks of traditional (TRAD) and eccentric-enhanced (ECC+) progressive resistance training and to compare the acute postexercise total testosterone (TT), bioavailable testosterone (BT), growth hormone (GH), and lactate responses in TRAD- and ECC+-trained individuals. Twenty-two previously untrained men (22.1 +/- 0.8 years) completed 1 familiarization and 2 baseline bouts, 15 exercise bouts (i.e., 3 times per week for 5 weeks), and 2 postintervention testing bouts. Anthropometric and 1 repetition maximum (1RM) measurements (i.e., bench press and squat) were assessed during both baseline and postintervention testing. Following baseline testing, participants were randomized into TRAD (4 sets of 6 repetitions at 52.5% 1RM) or ECC+ (3 sets of 6 repetitions at 40% 1RM concentric and 100% 1RM eccentric) groups and completed the 5-week progressive resistance training protocols. During the final exercise bout, blood samples acquired at rest and following exercise were assessed for serum TT, BT, GH, and blood lactate. Both groups experienced similar increases in bench press (approximately 10%) and squat (approximately 22%) strength during the exercise intervention. At the conclusion of training, postexercise TT and BT concentrations increased (approximately 13% and 21%, respectively, p < 0.05) and GH concentrations increased (approximately 750-1200%, p < 0.05) acutely following exercise in both protocols. Postexercise lactate accumulation was similar between the TRAD (5.4 +/- 0.4) and ECC+ (5.6 +/- 0.4) groups; however, the ECC+ group's lactate concentrations were significantly lower than those of the TRAD group 30 to 60 minutes into recovery. In conclusion, TRAD training and ECC+ training appear to result in similar muscular strength adaptations and neuroendocrine responses, while postexercise lactate clearance is enhanced following ECC+ training.     

Repeated bout effect is not correlated with intraindividual variability during muscle-damaging exercise

The aim of this study was to test the hypothesis that the repeated bout effect depends on intraindividual variability during a second bout of eccentric exercise. Eleven healthy men performed 2 resistance training bouts consisting of maximal eccentric exercise (EE1 and EE2) using the knee extensor muscles. The interval between the exercise bouts was 2 weeks and consisted of 10 sets of 12 repetitions at 160° · s(-1). Maximal isokinetic concentric torque at 30° · s(-1) was measured before the bouts and 2 minutes and 24 hours thereafter. Muscle soreness score and creatine kinase activity were determined before and after exercise. Intraindividual variability in torque during each eccentric repetition was measured during exercise. Repeated bout effect manifested after EE2: Muscle soreness was less, the shift in optimal knee joint angle to a longer muscle length was less, and the decrease in isokinetic concentric torque 2 minutes after exercise was less for EE2 compared with that for EE1. During concentric (isokinetic) contraction, length-dependent changes in isokinetic torque (IT) occurred after both EE1 and EE2: The shorter the muscle length, the greater the change in IT. There was a significant relationship between the decrease in maximal isokinetic knee extension torque 24 hours after EE1 and intraindividual variability of EE1 (R2 = 0.71, p < 0.05), but this relationship was not significant for EE2 (R2 = 0.18). It seems that intraindividual variability during eccentric exercise protects against muscle fatigue and damage during the first exercise bout but not during a repeat bout. These findings may be useful to coaches who wish to improve muscle function in resistance training with less depression in muscle function and discomfort of their athletes, specifically, when muscle is most sensitive to muscle-damaging exercise.     

beta2-Adrenergic receptor downregulation and performance decrements during high-intensity resistance exercise overtraining.

Previous research on overtraining due to excessive use of maximal resistance exercise loads [100% 1 repetition maximum (1 RM)] indicates that peripheral muscle maladaptation contributes to overtraining-induced performance decrements. This study examined the cellular and molecular responses of skeletal muscle to performance decrements due to high-relative-intensity (%1 RM) resistance exercise overtraining. Weight-trained men were divided into overtrained (OT, n = 8) and control (Con, n = 8) groups. The OT group performed 10 x 1 at 100% 1 RM daily for 2 wk, whereas the Con group performed normal training 2 days/wk. Muscle biopsies from the vastus lateralis muscle, voluntary static and dynamic muscle performances, and nocturnal urinary epinephrine were assessed before (pre) and after (post) overtraining. Overtraining occurred as indicated by a decrease in 1-RM strength for the OT group (mean +/- SE; OT pre = 159.3 +/- 10.1 kg, OT post = 151.4 +/- 9.9 kg, Con pre = 146.0 +/- 12.9 kg, Con post = 144.9 +/- 13.3 kg), as well as a 36.3% decrease in mean power at 100% 1-RM loads. Normal training could be resumed only after 2-8 wk of training cessation. Muscle beta(2)-adrenergic receptor (beta(2)-AR; fmol/mg protein) density significantly decreased by 37.0% for the OT group and was unchanged for the Con group (-1.8%). Nocturnal urinary epinephrine for the OT group increased by 49%, although this was not significant (effect size = 0.42). The ratio of nocturnal urinary epinephrine to beta(2)-AR density suggested a decreased beta(2)-AR sensitivity for the OT group (2.4-fold increase). Overtraining occurred based on decreased muscular force and power. Desensitization of the beta(2)-AR system suggests that this may be an important contributor to performance decrements due to excessive use of maximal resistance exercise loads.     

Electromyographic evidence of selective fatigue during the eccentric phase of stretch/shortening cycles in man

Ten male subjects were tested to determine the effects of muscle fatigue upon the activation pattern of the two main ankle extensor muscles, the 'slow-twitch' soleus (SOL) and the relatively 'fast-twitch' medial gastrocnemius (MG), during a fatiguing 60-s trial of hopping to maximal height. The myoelectric signals from SOL and MG were recorded together with the vertical ground reaction force signal and analysed by means of a computer-aided electromyograph (EMG) contour analysis, i.e. two-dimensional frequency distributions were obtained relating the activation patterns of the two synergists. The EMGs were also full-wave rectified and integrated (IEMG) according to three phases of the hopping movement (PRE, pre-activation phase; ECC, eccentric phase; CON, concentric phase). Results indicated that there were significant decreases (P less than 0.01) in the peak ground reaction force, the height of hopping and the mechanical power per unit body weight at the end of the fatiguing contractions. These decreases in mechanical parameters were accompanied by significant (P less than 0.01) decreases in all three phases of MG IEMG while SOL IEMG showed no such significant declines, except in the CON phase. Thus, the decreased mechanical parameters could in large part be accounted for by the substantial and selective decline of the excitation level of the relatively fast-twitch MG muscle. Our data suggest that the centrally mediated pre-activation of the fatiguable MG muscle as well as the MG activation during the eccentric phase, which is largely controlled by supraspinal inputs and stretch-reflex modulation, are most affected by fatigue changes during repeated maximal stretch/shortening cycles of the ankle extensors.     

Temporal strength changes from resistance exercise and albuterol on unloaded muscle

To assess unloaded knee extensor temporal strength changes, healthy subjects without asthma performed 40 continuous days of unilateral limb suspension, whereby their left leg refrained from normal weight-bearing and ambulatory activity. During the 40-day period, subjects performed resistance exercise (REX) with their unloaded leg on an inertial resistance ergometer and, as part of a double-blind design, consumed the maximal oral therapeutic dosage of albuterol (i.e., 16 mg.d) or a placebo (i.e., lactose) with no crossover. Workout data were partitioned into 4 10-day periods that ran consecutively. Dependent strength variables included concentric total work, eccentric total work, concentric average power (CAP), and eccentric average power (EAP). Dependent variables were analyzed with 5 (time) x 2 (group) x 2 (gender) mixed factorial analyses of variance and the Tukey honestly significant difference test. Concentric total work, CAP, and EAP each demonstrated a time-group-gender (p < 0.05) interaction. Female REX-placebo subjects had the greatest percentage of unloaded knee extensor strength loss. However, female REX-albuterol subjects fared best throughout the 40-day period and incurred significant unloaded knee extensor strength gains. Differences in strength changes between male and female REX-albuterol subjects was likely due to the higher relative dosage administered to the latter, as body mass showed a gender (i.e., men > women) effect. Future research may elucidate the ideal dose-response relationship for REX-albuterol treatment for use aboard manned space flights and in other disuse models. Coaches and practitioners should carefully examine their sport-governing bodies' rules on albuterol administration and give the drug only if an athlete's health warrants such treatment.     

The effects of EMG biofeedback on strength acquisition

This study investigated the effectiveness of electromyographic (EMG) biofeedback in maximizing strength gains and integrated electromyographic (IEMG) levels of the quadriceps muscle group resulting from an isokinetic exercise program. Twenty-one male volunteers recruited from physical education classes at a large southwestern university were randomly assigned to one of the following three treatment groups: (1) a biofeedback (BF) trained group, (2) a deception (DEC) trained group, and (3) a nonfeedback (NF) trained group. Subjects were trained and tested for strength by extension on a Cybex Isokinetic Exercise Machine at a speed of 30 degrees per second. Training sessions were performed three times per week for five weeks; pretest and posttest data were based on the best score of three trials of a 1-RM maximum effort. A pretraining to posttraining comparison indicated significant increases in strength (p less than .001) and IEMG levels (p less than .001) for all treatment groups when a paired t test was applied to the data. A multivariate analysis of covariance (MANCOVA) revealed that the BF trained group showed significantly greater peak torque values than DEC and NF trained groups (p less than .01) and produced significantly greater IEMG levels than the NF trained group (p less than .05). Overall, these results were taken as supporting the hypothesis that a training program of combined isokinetics and EMG biofeedback produces significant gains in maximal force and IEMG activity of leg-extensor muscles.     

Comparison of early phase adaptations for traditional strength and endurance, and low velocity resistance training programs in college-aged women

The purpose of this study was to investigate the effects of a six-week (16-17 training sessions) low velocity resistance training program (LV) on various performance measures as compared to a traditional strength (TS) and a traditional muscular endurance (TE) resistance training program. Thirty-four healthy adult females (21.1 +/- 2.7 y) were randomly divided into 4 groups: control (C), TS, TE, and LV. Workouts consisted of 3 exercises: leg press (LP), back squat (SQ), and knee extension (KE). Each subject was pre- and posttested for 1 repetition maximum (1RM), muscular endurance, maximal oxygen consumption (VO2max), muscular power, and body composition. After the pretesting, TS, TE, and LV groups attended a minimum of 16 out of 17 training sessions in which the LP, SQ, and KE were performed to fatigue for each of 3 sets. For each training session, TS trained at 6-10 RM and TE trained at 20-30 RM both with 1-2 second concentric/1-2 second eccentric; and LV trained at 6-10 RM, with 10 second concentric/4 s eccentric. Statistical significance was determined at an alpha level of 0.05. LV increased relative LP and KE 1 RM, but the percent increase was smaller than TS, and not different from C in the SQ. For muscular endurance, LV improved similarly to TE for LP and less than TS and TE for KE. Body composition improved for all groups including C (significant main effect). In conclusion, muscular strength improved with LV training however, TS showed a larger improvement. Muscular endurance improved with LV training, but not above what TE or TS demonstrated. For all other variables, there were no significant improvements for LV beyond what C demonstrated.     

Comparison of loaded and unloaded jump squat training on strength/power performance in college football players

The purpose of this study was to explore the effects of 5 weeks of eccentrically loaded and unloaded jump squat training in experienced resistance-trained athletes during the strength/ power phase of a 15-week periodized off-season resistance training program. Forty-seven male college football players were randomly assigned to 1 of 3 groups. One group performed the jump squat exercise using both concentric and eccentric phases of contraction (CE; n = 15). A second group performed the jump squat exercise using the concentric phase only (n = 16), and a third group did not perform the jump squat exercise and served as control (CT; n = 16). No significant differences between the groups were seen in power, vertical jump height, 40-yd sprint speed and agility performance. In addition, no differences between the groups were seen in integrated electromyography activity during the jump squat exercise. Significant differences between the CE and CT groups were seen in Delta 1RM squat (65.8 and 27.5 kg, respectively) and Delta 1RM power clean (25.9 and 3.8 kg, respectively). No other between-group differences were observed. Results of this study provide evidence of the benefits of the jump squat exercise during a short-duration (5-week) training program for eliciting strength and power gains. In addition, the eccentric phase of this ballistic movement appears to have important implications for eliciting these strength gains in college football players during an off-season training program. Thus, coaches incorporating jump squats (using both concentric and eccentric phases of contraction) in the off-season training programs of their athletes can see significant performance improvements during a relatively short duration of training.     

Effects of creatine supplementation and resistance training on muscle strength and weightlifting performance

Creatine monohydrate has become the supplement of choice for many athletes striving to improve sports performance. Recent data indicate that athletes may not be using creatine as a sports performance booster per se but instead use creatine chronically as a training aid to augment intense resistance training workouts. Although several studies have evaluated the combined effects of creatine supplementation and resistance training on muscle strength and weightlifting performance, these data have not been analyzed collectively. The purpose of this review is to evaluate the effects of creatine supplementation on muscle strength and weightlifting performance when ingested concomitant with resistance training. The effects of gender, interindividual variability, training status, and possible mechanisms of action are discussed. Of the 22 studies reviewed, the average increase in muscle strength (1, 3, or 10 repetition maximum [RM]) following creatine supplementation plus resistance training was 8% greater than the average increase in muscle strength following placebo ingestion during resistance training (20 vs. 12%). Similarly, the average increase in weightlifting performance (maximal repetitions at a given percent of maximal strength) following creatine supplementation plus resistance training was 14% greater than the average increase in weightlifting performance following placebo ingestion during resistance training (26 vs. 12%). The increase in bench press 1RM ranged from 3 to 45%, and the improvement in weightlifting performance in the bench press ranged from 16 to 43%. Thus there is substantial evidence to indicate that creatine supplementation during resistance training is more effective at increasing muscle strength and weightlifting performance than resistance training alone, although the response is highly variable.