Brendan Humphries

The optimal training load for the development of dynamic athletic performance

This study was performed to determine which of three theoretically optimal resistance training modalities resulted in the greatest enhancement in the performance of a series of dynamic athletic activities. The three training modalities included 1) traditional weight training, 2) plyometric training, and 3) explosive weight training at the load that maximized mechanical power output. Sixty-four previously trained subjects were randomly allocated to four groups that included the above three training modalities and a control group. The experimental groups trained for 10 wk performing either heavy squat lifts, depth jumps, or weighted squat jumps. All subjects were tested prior to training, after 5 wk of training and at the completion of the training period. The test items included 1) 30-m sprint, 2) vertical jumps performed with and without a countermovement, 3) maximal cycle test, 4) isokinetic leg extension test, and 5) a maximal isometric test. The experimental group which trained with the load that maximized mechanical power achieved the best overall results in enhancing dynamic athletic performance recording statistically significant (P < 0.05) improvements on most test items and producing statistically superior results to the two other training modalities on the jumping and isokinetic tests.

Influence of load and stretch shortening cycle on the kinematics, kinetics and muscle activation that occurs during explosive upper-body movements

Abstract Although explosive power in lower-body movements has been extensively studied, there is a paucity of research examining such movements in the upper body. This study aimed to investigate the influence of load and the stretch shortening cycle (SSC) on the kinematics, kinetics, and muscle activation that occurs during maximal effort throws. A total of 17 male subjects performed SSC and concentric only (CO) bench throws using loads of 15%, 30%, 45%, 60%, 75%, 90% and 100% of their previously determined one repetition maximum bench press. The displacement, velocity, acceleration, force and power output as well as the electromyogram (EMG) from pectoralis major, anterior deltoid, and triceps brachii were recorded for each throw. The results were compared using multivariate analysis of variance with repeated measures. A criterion alpha level of P ≤ 0.05 was used. Similar force velocity power relationships were determined for this multijoint upper-body movement as has been found for isolated muscles, single joint movements, and vertical jumping. The highest power output was produced at the 30% [563 (104) W] and 45% [560 (86) W] loads during the SSC throws. Force output increased as a function of load; however, even the lighter loads resulted in considerable force due to the high accelerations produced. Average velocity, average and peak force, and average and peak power output were significantly higher for the SSC throws compared to the CO throws. However, peak velocity and height thrown were not potentiated by performing the pre-stretch because the duration and range of movement allowed the ability of the muscle to generate force at high shortening velocities to dominate the resulting throw. As such, explosive movements involving longer concentric actions than experienced during brief SSC movements may be limited by the ability of the muscle to produce force during fast contraction velocities.

Determining the optimal load for jump squats: a review of methods and calculations.

There has been an increasing volume of research focused on the load that elicits maximum power output during jump squats. Because of a lack of standardization for data collection and analysis protocols, results of much of this research are contradictory. The purpose of this paper is to examine why differing methods of data collection and analysis can lead to conflicting results for maximum power and associated optimal load. Six topics relevant to measurement and reporting of maximum power and optimal load are addressed: (a) data collection equipment, (b) inclusion or exclusion of body weight force in calculations of power, (c) free weight versus Smith machine jump squats, (d) reporting of average versus peak power, (e) reporting of load intensity, and (f) instructions given to athletes/ participants. Based on this information, a standardized protocol for data collection and reporting of jump squat power and optimal load is presented.

The effect of short-term Swiss ball training on core stability and running economy.

&NA; Stanton, R., P. Reaburn, and B. Humphries. The effect of short‐term Swiss ball training on core stability and running economy. J. Strength Cond. Res. 18(3):522–528. 2004.—The purpose of this study was to investigate the effect of a shortterm Swiss ball training on core stability and running economy. Eighteen young male athletes (15.5 ± 1.4 years; 62.5 ± 4.7 kg; &Egr;9 skinfolds 78.9 ± 28.2 mm; SymbolO2max 55.3 ± 5.7 ml·kg‐1·min‐1) were divided into a control (n = 10) and experimental (n = 8) groups. Athletes were assessed before and after the training program for stature, body mass, core stability, electromyographic activity of the abdominal and back muscles, treadmill SymbolO2max, running economy, and running posture. The experimental group performed 2 Swiss ball training sessions per week for 6 weeks. Data analysis revealed a significant effect of Swiss ball training on core stability in the experimental group (p < 0.05). No significant differences were observed for myoelectric activity of the abdominal and back muscles, treadmill SymbolO2max, running economy, or running posture in either group. It appears Swiss ball training may positively affect core stability without concomitant improvements in physical performance in young athletes. Specificity of exercise selection should be considered. Symbol. No caption available.

Myoelectric evidence of peripheral muscle fatigue during exercise in severe hypoxia: some references to m. vastus lateralis myosin heavy chain composition

Abstract Integrated electromyography (iEMG) of the m. vastus lateralis was analysed during cycle ergometry in male subjects (n = 8). Two work trials were conducted, one under normoxia (N), the other under environmental normobaric hypoxia (EH in which the oxygen fraction in inspired gas = 0.116), each trial lasting 10 min. The absolute power output (180 W) was the same for both trials and was equivalent to 77 (4)% of maximum heart rate in trial N. Maximal voluntary isometric contractions were performed after each trial to assess changes in force, muscle fibre conduction velocity (MFCV), electromechanical delay (EMD), median frequency of EMG (MF) and maximal iEMG (iEMGmax). Biopy samples of muscle were obtained from the m. vastus medialis before testing. Myosin heavy chain (MHC) differences were determined through sodium dodecyl-polyacrylamide gel electrophoresis followed by densitometric analysis. No differences in submaximal iEMG were observed between EH and N trials during the first minute of work. At the end of both work trials iEMG was significantly elevated compared with starting values, however the iEMG recorded in EH exceeded N values by 15%. At the end of the EH trials the following were observed: a decrease in isometric force, MFCV and MF with an increase in EMD and the iEMGmax/force ratio. The iEMGmax was unchanged. No differences in any of these variables were observed after the N trial. Mean (SD) lactate concentrations following EH and N trials were 9.2 (4.4) mmol · 1−1 and 3.5 (1.1) mmol · 1−1, respectively. Results indicate that an increased motor unit recruitment and rate coding was needed in EH to maintain the required power output. The increased motor unit recruitment and rate coding were associated with myoelectric evidence of “peripheral” muscle fatigue. Subjects with higher compositions of type II MHC accumulated more lactate and displayed greater reductions in MF and MFCV during fatigue.

Effect of exercise intensity on bone density, strength, and calcium turnover in older women

PURPOSE This study examined the effects of 24 wk of high intensity strength training or low intensity walking on lumbar bone mineral density (BMD), muscular strength, and calcium turnover in Australian women either taking hormone replacement therapy (HRT) or not taking HRT. METHODS A subject pool of 64 women between 45-65 yr and randomly allocated into weights (N = 21), walking (N = 20), weightsHRT (N = 14), and walkingHRT (N = 9) groups completed this study. All subjects trained twice weekly in either a 50-min walking or weight-training program (60-90% IRM). Measurements included maximal isometric knee strength, IRM bench press, IRM squat, isokinetic back strength, lumbar (L2-L4) BMD, serum osteocalcin, and urinary deoxypyridinoline crosslinks (Dpd). RESULTS No significant group differences in BMD were evident at the completion of training. However, a significant (P < 0.05) within group change was apparent for the walking group since BMD decreased 1.3% below baseline testing. Osteocalcin levels increased significantly (P < 0.05) in the walking (22%) group. Maximal bench press and squat strength improved significantly (P < 0.05) in the weights (25.8% and 37.7%) and weightsHRT (25.4% and 35.7%) groups. The weights group also increased significantly (P < 0.05) in isokinetic back strength (22.2%). CONCLUSION It was concluded that short-term high intensity resistance training provides an effective means for increasing muscular strength in women between 45 and 65 yr. The training effects on lumbar BMD were not apparent in the present study.

1,1,1-Trichloro-2,2-bis (p-Chlorophenyl)-Ethane (DDT) and Reduced Bone Mineral Density

Abstract The organochlorine pesticide 1,1,1-trichloro-2,2-bis (p-chlorophenyl)-ethane (DDT), is a well-known and widely dispersed “environmental estrogen” (World Health Organization Criteria no. 9; Geneva, Switzerland [1979]). Kelce et al. (Nature, 1995; 375:581–85) recently identified the DDT metabolite, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), has also recently been identified as a potent androgen receptor antagonist. The authors examined the relationship between serum levels of DDE and bone mineral density in 68 sedentary women who reported adequate dietary intake of calcium. Reduced bone mineral density was correlated significantly with age (r = -.36, p = .004), as well as with increases in the log of DDE levels in serum (r = -.27, p = .03). The authors also used multiple-regression analysis to examine the influence of other predictor variables on the relationship between log DDE and bone mineral density. The strongest model (p = .002) included log DDE (p = .018), age (p = .002), and years on hormone replacement therapy (p = .10) as predictor variables, and this model afforded prediction of 21% of bone mineral density variation. These results suggest that past community exposures to DDT may be associated with reduced bone mineral density in women.

Female collegiate windmill pitchers: influences to injury incidence.

&NA; Hill, J.L., B. Humphries, T. Weidner, and R.U. Newton. Female collegiate windmill pitchers: Influences to injury incidence. J. Strength Cond. Res. 18(3):426–431.—Few studies have examined fast‐pitch softball pitchers and associated injuries. The aim of this study was to investigate injuries occurring to collegiate softball pitchers and associated influential factors. A web‐based survey of 181 Division I (n = 45), II (n = 30), and III (n = 54) collegiate softball pitchers was conducted. The survey involved self‐reported data from the previous year that addressed (a) demographic information, (b) pitching and game data, (c) training program information, and (d) injury reporting. Demographic information, pitching and game data, and training program information were not statistically significant (p < 0.05) in relation to injury. Descriptive statistics were used to report totals and percentages of pitchers surveyed. Among 131 reported injuries, 36 were acute, 92 chronic/overuse, and 3 unspecified. Of the total injuries, 80 were directly from pitching, with 33 shoulder‐related and 16 related to the lower back. Among injured pitchers, 109 took nonsteroidal anti‐inflammatory drugs, 140 used modalities, 11 received surgeries, and 95 saw additional specialists. Pitchers are at a risk for injury, with 72.8% of surveyed pitchers being injured during the 2001–02 year.

Whole-Body Vibration Effects on Bone Mineral Density in Women with or Without Resistance Training

INTRODUCTION Whole-body vibration exposure may translate into improved bone mass in young adult women. The primary focus of this study was to examine the effects of graded whole-body vibration or vibration exposure plus resistance training on bone mineral density (BMD), hematological measures for bone remodeling, and exercise metabolism in young women. METHODS There were 51 healthy active women [mean (SD) age, 21.02 (3.39) yr; height, 165.66 (6.73) cm; body mass 66.54 (13.39) kg] who participated in the intervention. Subjects were randomly assigned to whole-body vibration (WBV), whole-body vibration plus resistance training (WBV+RT), or control (CONT) groups for 16 wk. RESULTS A repeated-measure ANOVA found no significant (P < 0.05) group differences in BMD at the completion of 16 wk. A significant within group change was apparent for the WBV (2.7% femoral neck) and WBV+RT (femoral neck 1.9%; vertebra 0.98%). WBV and WBV+RT experienced a significant (P < 0.05) 60% and 58% increase in adiponectin, 48% and 30% in transforming growth factor-beta1, and 17% and 34% in nitric oxide with an accompanying 50% and 36% decrease in osteopontin, 19% and 34% in interleukin-1beta, and 38% and 39% in tumor necrosis factor-alpha. CONCLUSIONS The results indicate graded whole-body vibration exposure may be effective in improving BMD by increasing bone deposition while also decreasing bone resorption. Whole-body vibration may also provide an efficient stratagem for young women to achieve peak bone mass and help stave off osteoporosis later in life and provide a novel form of physical training.

Prevalence and correlates of resistance training in a regional Australian population

Background The core components of physical activity, cardiovascular endurance, muscular strength, balance and flexibility can provide many health benefits and potentially slow declines associated with aging. Aerobic exercise message to the public has been widely promoted by national health authorities, although the promotion of resistance training has received far less attention. Objectives n this research, the prevalence of resistance training in a sample of adults living in regional Australia was primarily assessed. Design A computer-assisted telephone interview survey (n=1230) was conducted by the Population Research Laboratory at Central Queensland University on Queensland adults in October to November 2006. Respondents were asked to report the frequency with which they engaged in resistance training. Participants Respondents were 18 years or older that could be contacted by direct-dialled, land-based telephone service. A telephone database using a computer program to select, with replacement, a simple random sample of phone numbers selected respondents. Results Almost 14% of the population did some form of gym-based resistance training in the week before the survey. There was a significant (p<0.05) reduction in participation levels with age. Participation was highest amongst the youngest 18–34-year-olds (23.8%), steadily declining with age to a low of 7% in the 55 years and older age group. There was no significant association between sexes and participation in resistance training. Conclusions The findings underscore the need to increase overall education on the benefits of resistance training with an emphasis among targeted adult populations to increase participation in resistance training.