Loren Z. F. Chiu

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.

Anthropometric and performance variables discriminating elite American junior men weightlifters.

The purpose of this study is to identify physical and performance variables that discriminate elite American junior-aged men weightlifters from nonelite performers. Using a cross-sectional design, multiple discriminant analysis was used to determine field tests identifying elite male junior weightlifters. Young men who were participants (n = 115) at the Junior National and Junior Olympics Weightlifting Championships volunteered as subjects (mean ± SD age = 14.8 ± 2.3 years). Elite weightlifters (n = 20) were identified as the top 17.5% of national-level competitors when weightlifting performances were adjusted for body mass using the Sinclair equation. All other weightlifters were classified as nonelite (n = 95). Test batteries were performed immediately upon completion of a national-level weightlifting competition. Variables measured included easily-administered field tests of physical dimensions and body composition, muscular strength and power, flexibility, and gross motor control. The resulting regression equations correctly classified 84.35% of the weightlifters as elite or nonelite. Five variables significantly contributed to the discriminant analysis (Wilks Λ= 0.6637392, χ2= 44.880, df = 5, p < 0.0001, adjusted R2 = 0.67). Body mass index accounted for 23.13% of the total variance, followed by vertical jump (22.78%), relative fat (18.09%), grip strength (14.43%), and torso angle during an overhead squat (0.92%). The use of these 5 easily administered field tests is potentially useful as a screening tool for elite American junior men weightlifters.

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.

Comparison of joint kinetics during free weight and flywheel resistance exercise.

The most common modality for resistance exercise is free weight resistance. Alternative methods of providing external resistance have been investigated, in particular for use in microgravity environments such as space flight. One alternative modality is flywheel inertial resistance, which generates resistance as a function of the mass, distribution of mass, and angular acceleration of the fly-wheel. The purpose of this investigation was to characterize net joint kinetics of multijoint exercises performed with a flywheel inertial resistance device in comparison to free weights. Eleven trained men and women performed the front squat, lunge, and push press on separate days with free weight or flywheel resistance, while instrumented for biomechanical analysis. Front squats performed with flywheel resistance required greater contribution of the hip and ankle, and less contribution of the knee, compared to free weight. Push presses performed with flywheel resistance had similar impulse requirements at the knee compared to free weight, but greater impulse requirement at the hip and ankle. As used in this investigation, flywheel inertial resistance increases the demand on the hip extensors and ankle plan-tarflexors and decreases the mechanical demand on the knee extensors for lower extremity exercises such as the front squat and lunge. Exercises involving dynamic lower and upper extremity actions, such as the push press, may benefit from flywheel inertial resistance, due to the increased mechanical demand on the knee extensors.

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.

Myosin heavy chain isoform expression and in vivo isometric performance: a regression model.

This investigation estimated the amount of variance in voluntary in vivo muscle performance that can be explained by relative myosin heavy chain (MHC) isoform expression. The role of the relative expression of these proteins in relation to in vitro force and velocity performance is well understood, but the in vivo model is less clear. Twenty-two men and women (mean ± SD age, 27 ± 6 years) performed isometric knee extensor actions in which peak force and rate of force development (RFD) were measured. The results of regression analysis showed that the inclusion of MHC IIb explained a significant (19.9%, p < 0.05) amount of variance in relative peak force (adjusted for muscle mass) and 14.1% of the variance in the first half of the rise phase of the force-time curve (RFD0–50%)(p < 0.1). The addition of MHC I into this model explained a significant (p < 0.05) amount of variance above that accounted for by MHC IIb in RFD (45.4%), RFD0–50% (50.8%), and RFD50–100% (second half of the rise phase of the force-time curve) (37.4%). Since the percentage of MHC IIb is reduced rather quickly with training, these data suggest that peak force may also be affected quickly by training. The percentage of MHC I has a longer course for change with training; therefore, it may be inferred that the greatest changes in RFD variables will likely occur during a longer course.

Muscle Fiber and Performance Adaptations to Resistance Exercise with MyoVive, Colostrum or Casein and Whey Supplementation

To determine the effects of 12 weeks of resistance exercise with MyoViveo and/or colostrum supplementation, 19 male and female recreationally weighttrained subjects (X ‐ SE; age = 28.3 ‐ 6.9 yrs; hgt = 68.2 ‐ 3.8 cm) were divided into MyoViveo + colostrum (n = 4), MyoViveo + casein & whey (n = 4), colostrum + casein & whey (n = 6), and casein & whey (n = 5) groups. All groups similarly increased (p < .05) 1 repetition maximum (RM) leg press (kg; pre = 158.6 ‐ 12.8, post = 189.3 ‐ 11.3), body mass (kg; pre = 79.0 ‐ 3.2, post = 80.7 ‐ 3.8), and lean body mass (kg; pre = 60.1 ‐ 3.1, post = 62.2 ‐ 2.8). Increases were observed for peak force (N; all loads), peak velocity (m . s -1 ; 70% & 40% 1 RM), and peak power (W; 70% & 40% 1 RM) for all groups for the leg press exercise, with no differences between groups. When performance data were adjusted for body mass, lean body mass, lower body lean mass as determined by DEXA, or % change, no group differences were observed. Relative (%) fiber type content, cross-sectional areas (mm 2 ), % fiber type areas, or % myosin heavy chain expression did not change for any group. These data suggest that MyoViveo and colostrum supplementation have no greater effect on cellular and performance adaptations when compared to casein and whey protein.

The influence of deformation on barbell mechanics during the clean pull

For simplicity of biomechanical analyses, the weightlifting barbell is typically modelled as a rigid, non-deformable object. Most coaches and weightlifters, however, are aware of the elastic nature of the barbell, and its influence on the successful completion of lifting attempts. Variables such as velocity, work performed, and power output are indicators of the quality of performance during the snatch, clean, and related weightlifting pulling movements. The aim of this study was to establish whether differences exist in determining these biomechanical parameters when the centre of the barbell is analysed compared with each end of the barbell. Nine men performed three maximal-effort repetitions in the clean pull exercise at 85% of their self-reported single repetition maximum (1-RM) clean (90–155 kg) using a barbell instrumented for mechanical analysis. Results indicated that peak barbell speed was 5–30% (P < 0.05) lower for the centre of the barbell than the ends. Although differences (P < 0.05) in kinetic and potential energy were found between the centre and ends of the bar, differences between total work performed were small ( < 6%; P < 0.05) and no differences were observed for average power (P > 0.05). Although approximately the same work and power occur for the centre and ends of the barbell, they manifest as different kinematics as a result of the elastic nature of the equipment. The elastic characteristics should be considered when selecting instrumentation and variables for research involving barbells. Coaches should be aware of the elasticity of barbells, including selecting appropriate viewing angles as well as understanding how deformation may affect the ends of the barbell relative to the centre.

MYOSIN HEAVY CHAIN ISOFORM EXPRESSION: INFLUENCE ON ISOINERTIAL AND ISOMETRIC PERFORMANCE

Thirty-six healthy men with varying degrees of physical training background performed maximal-effort isometric and isoinertial knee extensor actions, with relative loads equal to 40% and 70% of one-repetition maximum. Force, velocity, and power were derived from force and linear position transducers at 500 Hz. Biopsies were taken from the vastus lateralis and analyzed by SDS-PAGE for relative myosin heavy chain (MHC) content. Relative MHC IIx content was included in a regression model, and explained variance noted. Relative MHC I content was subsequently added to the regression model to determine what, if any, additional variance was explained beyond that of MHC IIx. Results indicated that no relationship (r = 0.0 to 0.1) exists between the relative expression of MHC isoforms from the vastus lateralis and isometric/isoinertial performance in a population with diverse training backgrounds. Lack of nervous system adaptations in the untrained subjects in the study possibly attenuates the significant relationship between MHC and in-vivo muscle performance previously established in trained populations.