Lawrence W. Weiss

Postactivation potentiation response in athletic and recreationally trained individuals.

To determine if training status directly impacted the response to postactivation potentiation, athletes in sports requiring explosive strength (ATH; n = 7) were compared to recreationally trained (RT; n = 17) individuals. Over the course of 4 sessions, subjects performed rebound and concentric-only jump squats with 30%, 50%, and 70% 1 RM loads. Jump squats were performed 5 minutes and 18.5 minutes following control or heavy load warm-ups. Heavy load warm-up consisted of 5 sets of 1 repetition at 90% 1 RM back squat. Jump squat performance was assessed with a force platform and position transducer. Heavy load warm-up did not have an effect on the subjects as a single sample. However, when percent potentiation was compared between ATH and RT groups, force and power parameters were significantly greater for ATH (p < 0.05). Postactivation potentiation may be a viable method of acutely enhancing explosive strength performance in athletic but not recreationally trained individuals.

Relationship of jumping and agility performance in female volleyball athletes.

Court sports often require more frequent changes of direction (COD) than field sports. Most court sports require 180= turns over a small distance, so COD in such sports might be best evaluated with an agility test involving short sprints and sharp turns. The purposes of this study were to (a) quantify vertical and horizontal force during a COD task, (b) identify possible predictors of court-sport–specific agility performance, and (c) examine performance difference between National Collegiate Athletic Association Division I, II, and III athletes. Twenty-nine collegiate female volleyball players completed a novel agility test, countermovement (CM) and drop jump tests, and an isometric leg extensor test. The number of athletes by division was as follows: I (n = 9), II (n = 11), and III (n = 9). The agility test consisted of 4 5-meter sprints with 3 180= turns, including 1 on a multiaxial force platform so that the kinetic properties of the COD could be identified. One-way analysis of variance revealed that Division I athletes had significantly greater countermovement jump heights than Division III, and the effect size comparisons (Cohens d) showed large-magnitude differences between Division I and both Divisions II and III for jump height. No other differences in performance variables were noted between divisions, although effect sizes reached moderate values for some comparisons. Regression analysis revealed that CM displacement was a significant predictor of agility performance, explaining approximately 34% of the variance. Vertical force was found to account for much of the total force exerted during the contact phase of the COD task, suggesting that performance in the vertical domain may limit the COD task used herein. This study indicates that individuals with greater CM performance also have quicker agility times and suggests that training predominantly in the vertical domain may also yield improvements in certain types of agility performance. This may hold true even if such agility performance requires a horizontal component.

Effect of rest interval length on repeated 1 repetition maximum back squats.

To examine the effects of different rest intervals on the repeatability of 1 repetition maximum (1RM) efforts in the free-weight back squat exercise, 17 weight-trained men served as subjects (mean age 22.0 years). One repetition maximum was tested on each of the first 2 days of testing to establish a stable baseline (1RM = 184.9 kg). Each of the next 3 sessions involved performing 2 1RM back squats, with the rest interval between attempted lifts being either 1, 3, or 5 minutes, assigned in a counterbalanced fashion. For the 1-minute rest interval, 13 of 17 subjects successfully completed the second lift; for the 3-minute rest interval, 16 of 17 were successful; and for the 5-minute rest interval, 15 of 17 were successful. Cochran Q analysis determined no significant difference (p > 0.05) in the ability to repeat a successful maximal-effort back squat when different rest intervals were used. These findings are consistent with the literature for the bench-press exercise and indicate that 1-minute rest intervals are sufficient for recovery between attempted lifts during 1RM testing or training for the free-weight back squat when involving lifters of this caliber.

Skeletal muscle and hormonal adaptations to circuit weight training in untrained men.

Twelve men either performed 10 weeks of timed circuit weight training 3 days week−1 (CWT; n=8; X±SE; age=23.6±1.8 years), or were part of a sedentary control group (n=4; age=20.5±1.0 years). Significance was P<0.05 for all analyses. The CWT program significantly increased 1 repetition maximum (1 RM) strength for nine of 10 exercises (15–42%). Although no body composition measure significantly changed for the CWT group, low‐to‐moderate effect sizes were evident for body weight, lean body mass, and relative fat. CWT did not alter percent fiber type, but did increase cross‐sectional areas for type IIA fibers (μm2; pre=5988±323, post=7259±669). Relative (%) myosin heavy‐chain (MHC) expression increased for MHC IIa (pre=42.5±2.7, post=50.1±2.6), and decreased for MHC IIb (pre=21.8±2.8, post=15.4±2.4) for the CWT group. Serum testosterone, cortisol, and the testosterone/cortisol ratio did not change at any time for the CWT group. None of the measured variables changed for the control group. These data indicate that for untrained subjects, CWT of the type used resulted in improved muscular strength and a tendency toward increased lean mass. Compared with other types of weight training, fewer adaptations of the muscle fibers were evident. This is likely due in part to the relatively low loads used with this type of resistance exercise.

Neuromuscular fatigue and potentiation following two successive high intensity resistance exercise sessions

Resistance exercise can result in both potentiating and fatiguing responses. These responses can acutely affect performance, which may affect subsequent exercise sessions in the same day. The purpose of this investigation was to study the acute neuromuscular responses to two high intensity training sessions in the same day. Twelve recreationally trained males performed two training sessions, each involving ten sets of five repetitions in the speed squat exercise. For the initial session (HIT-1), the barbell load was constant at 70% one repetition maximum, whereas during the second session (HIT-2), barbell load decreased if movement velocity decreased. Neuromuscular performance testing consisted of unilateral isometric knee extensor actions performed prior to the training day (PRE) and following each testing session. Prior to the sessions, subjects provided a muscle biopsy for myosin heavy chain analysis. Peak force was impaired 16.9 (9.5)% (P≈0.00; d=1.62) following HIT-1 and 19.9 (18.4)% (P≈0.00; d=1.94) following HIT-2. Initial rate of force development was depressed from PRE following HIT-1 (P≈0.00; d=1.74) and HIT-2 (P≈0.00; d=2.18); however, this was dependent on muscle fiber composition. Significant correlations existed between the change score for initial rate of force development from HIT-1 to HIT-2 and myosin heavy chain I (r= −0.60; P=0.04) and IIa (r=0.69; P=0.01) expression. Impaired neuromuscular performance following HIT-1 may occur due to low frequency fatigue. For individuals with predominantly myosin heavy chain IIa, HIT-2 appeared to induce post-activation potentiation, resulting in restoration of the initial rate of force development.

Impaired leg extensor strength in individuals with Parkinson disease and relatedness to functional mobility

Previous investigations have demonstrated leg strength deficits in persons with Parkinsons disease (PD) as compared to neurologically-normal adults. However, the exact mode of contraction by which strength is assessed may determine how closely such deficits are related to functional performance. The purpose of this study was to better understand the relationship of strength and functional mobility in persons with PD (n = 17, mean H&Y stage = 2.0) via comparison to a group of similar age healthy controls (n = 10) using a multi-joint isometric test of strength and various measures of functional mobility. Tests included isometric leg press maximum force relative to body mass, the Activities-specific Balance Confidence scale (ABC), postural sway under various unilateral stance and visual conditions, and the timed up and go (TUG). Relative force (p = 0.044) and ABC questionnaire mean scores (p < 0.001), showed controls performing better than PD subjects. The control group performed better than the PD group for length of path of the center of pressure except in the eyes closed positions (p < 0.05 for all). TUG time (p = 0.052) was not significantly different between the PD group and healthy controls. Leg press maximum force relative to body mass was however significantly correlated with TUG time (r = -0.68, p = 0.003) in persons with PD. There were no gender differences for any variables. These results suggest that some balance and functional mobility task performances are more worse for persons with mild-to-moderate PD than for neurologically-normal age-matched controls, which may be influenced by lessened lower extremity multi-joint strength. Strength training of the lower extremity utilizing such multi-joint actions may be beneficial for this population.

Acute effects of augmented eccentric loading on jump squat performance.

The purpose of this study was to determine the acute effects of a spectrum of eccentric loads on force, velocity, and power during the concentric portion of maximal-effort jump squats utilizing a repeated measures design. Thirteen resistance-trained men (age = 22.8 ± 2.9 years, weight = 87.1 ± 11.8 kg, 163.5 ± 28.6 kg squat 1 repetition maximum [1RM]; mean ± SD), who routinely incorporated back squats into their training, participated as subjects in this investigation. Jump squat performance was assessed using 4 experimental conditions. The first of these conditions consisted of an isoinertial load equal to 30% of back squat 1RM. The remaining conditions consisted of jump squats with a concentric load of 30% 1RM, subsequent to the application of experimental augmented eccentric loading (AEL) conditions of 20, 50, and 80% of back squat 1RM, respectively. All subjects performed 2 sets of 1RM of maximum- effort jump squats with all experimental conditions in a counter- balanced sequence. Forty-eight hours after completing the first testing session, subjects repeated the experimental testing protocol to establish stability reliability. Peak performance values for the reliable variables of force, velocity, and power, as well as force and power values obtained at 20-ms intervals during the initial 400 ms of the concentric jump squat range of motion, showed no statistical difference (p > 0.05) across the experimental AEL loads. These results suggest that load-spectrum AEL prior to a 30% 1RM jump squat fails to acutely enhance force, velocity, and power.

Reach Height and Jump Displacement: Implications for Standardization of Reach Determination

Ferreira, LC, Schilling, BK, Weiss, LW, Fry, AC, and Chiu, LZF. Reach height and jump displacement: implications for standardization of reach determination. J Strength Cond Res 24(6): 1596-1601, 2010-Vertical jump performance is often assessed using jump-and-reach tests. The exact procedure used for determining standing reach height and jump height has a large effect on the resultant displacement. The purpose of this investigation was to determine the influence of 4 methods of standing reach height measurement and Vertec™ jump height measurement against 2 force plate methods of jump displacement determination (impulse and flight-time methods). Fifteen men with various training backgrounds performed 2 each of countermovement, restricted (no arm swing) and static start vertical jumps. Reach height was determined using 4 methods; either a 1- or overlapped 2-hand reach, flat footed or with plantar flexion. All jumps were performed on a force platform. The best jump of each type based on Vertec™ displacement was used for analysis. Repeated-measures of analysis of variance for each jump type was used for analysis with Bonferroni post hoc for pairwise comparisons of jump measurement style. All jump displacements for similar types were significantly intercorrelated with a minimum r-value of 0.84. Impulse vs. flight time was the only pairwise comparison of measurement type for which similar values were noted. The one-hand reach with plantar flexion was the method of reach that was closest to the impulse and flight-time methods, and thus should be the preferred choice when using jump-and-reach tests to determine jump displacement. In all cases, the Vertec™ overestimates the displacement of the COM based on force plate methods. When comparing groups of individuals from different data sets, one must consider both the method of reach height (if performed) and jump displacement to make valid comparisons. If plantar flexion with a 1-hand reach is not used during reach measurement, jump displacement will be erroneously high.

Effects of Unstable Surface Training on Measures of Balance in Older Adults

Schilling, BK, Falvo, MJ, Karlage, RE, Weiss, LW, Lohnes, CA, and Chiu, LZF. Effects of unstable surface training on measures of balance in older adults. J Strength Cond Res 23(4): 1211-1216, 2009-The purpose of this investigation was to examine the effects of a 5-week, low-cost unstable surface balance training program in sexagenarians. Nineteen men and women (60-68 years; 83.7 ± SD kg) were randomly assigned to a control or training group. The training group performed various balance activities on air-filled rubber disks for 5 weeks. Each thrice-weekly session was supervised, and progression was based on proficiency. While in an upright position, static balance (length of path [LOP] of the center of pressure) was assessed in both eyes-open and eyes-closed states for each leg separately as well as for both legs. Participants also performed the timed up-and-go (TUG) test and completed the Activity-specific Balance Confidence (ABC) questionnaire. A significant group × time effect for the ABC questionnaire was found (p = 0.04). Tukey post hoc analysis indicates that the balance training program increased self-perceived balance confidence (p < 0.01). No significant group × time interactions were noted for TUG or LOP. Because no objective measure of balance or function was changed, the increase in ABC may be spurious. Unstable surface training may not be effective in improving balance among persons for whom balance is not problematic. However, the large number of acute training variables in such a program leaves opportunity for further research in this paradigm.

Contextual interference effect on acquisition and retention of pistol-shooting skills.

The effects of contextual interference on learning pistol-shooting skills in a natural training environment were examined. The shooting skills consisted of three “stages” with different requirements for the skill variations commonly used in the field. 12 participants were randomly assigned into one of two practice conditions, blocked vs serial. Following a 20-min. safety and skill instructional session, Blocked group practiced 10 trials in a row at each stage, while Serial group performed 5 trials in a row for each of the three stages and then repeated the cycle. Both groups completed a total of 30 practice trials over the three stages. A 10-min. rest interval was provided prior to a retention test which included 9 trials (3 trials at each stage in a blocked format). Results based on the data of Stage III, the most complex skill among the three stages, showed a pattern consistent with previous findings that practicing in the serial schedule depressed performance during initial training but maintained the performance better at retention, relative to the blocked practice.