C. Russell Hendrix

Gender Comparisons of Anthropometric Characteristics of Young Sprint Swimmers

Zuniga, J, Housh, TJ, Mielke, M, Hendrix, CR, Camic, CL, Johnson, GO, Housh, DJ, and Schmidt, RJ. Gender comparisons of anthropometric characteristics of young sprint swimmers. J Strength Cond Res 25(1): 103-108, 2011-The purpose of this study was to compare the body composition, body build, and anthropometric characteristics of boy and girl sprint swimmers. Two groups (boys, n = 38 and girls, n = 31) of sprint swimmers (mean age ± SD = 11.03 ± 2.29 and 10.45 ± 2.29 years, respectively) volunteered for this study. The subjects were members of local swimming clubs who competed in sprint swimming events (≤200 m). Gender comparisons were made for age, body weight (BW), height (HT), fat-free weight (FFW), percent body fat (%fat), endomorphic rating, mesomorphic rating, ectomorphic rating, sum of 12 diameters, sum of 11 circumferences, biacromial diameter/biiliac diameter, and FFW/HT. The results of the independent t-tests indicated that the only mean differences between the boy and girl sprint swimmers were for % fat (boys = 9.40 ± 5.35% fat; girls = 12.73 ± 6.19% fat) and endomorphic rating (boys = 2.87 ± 0.96; girls = 4.29 ± 1.22). For the current age group of sprint swimmers the only gender differences were for measures associated with body fatness, and there were no differences for body build measures associated with musculoskeletal size, muscularity, skeletal size, total body mass, or body breadth dimensions. These findings suggest that the swimming performance for girls may be improved through training programs designed to reduce body fatness.

The Effects of Creatine Monohydrate Loading on Anaerobic Performance and One-Repetition Maximum Strength.

Abstract Zuniga, JM, Housh, TJ, Camic, CL, Hendrix, CR, Mielke, M, Johnson, GO, Housh, DJ, and Schmidt, RJ. The effects of creatine monohydrate loading on anaerobic performance and one-repetition maximum strength. J Strength Cond Res 26(6): 1651–1656, 2012—The purpose of this study was to examine the effects of 7 days of supplementation with 20 g·d−1 of creatine monohydrate (CM) on mean power (MP) and peak power (PP) from the Wingate anaerobic test (WAnT), body weight (BW), 1-repetition maximum (1RM) bilateral leg extension (LE) strength, and 1RM bench press (BP) strength. This study used a randomized, double-blind, placebo-controlled design. Twenty-two men (mean ± SD: age = 22.1 ± 2.0 years; height = 178.0 ± 5.8 cm; body weight [BW] = 77.6 ± 7.6 kg) were randomly assigned to either a supplement (SUPP; n = 10) or placebo (PLAC; n = 12) group. The SUPP group ingested 20 g·d−1 of CM powder for 7 days, whereas the PLAC ingested 20 g·d−1 of maltodextrin powder. Measurements for the PLAC and SUPP groups included BW, PP, and MP from two 30-second WAnTs (separated by 7 minutes), and 1RM strength for LE and BP. Testing was conducted before (PRE) and after (POST) 7 days of ingesting either the supplement or placebo. The results of this study indicated that there was a significant (p ⩽ 0.05) increase from PRE to POST testing in MP for the SUPP group (5.4%) but not for the PLAC group (−0.3%). There were no between-group differences, however, for 1RM LE and 1RM BP strength. Furthermore, there were no changes in PP or BW for either group. The findings of this study indicated that loading with 20 g·d−1 of CM for 7 days increased MP (5.4% increase) from the WAnT, but it had no effect on strength (1RM LE and 1RM BP), PP, or BW.

Acute effects of a caffeine-containing supplement on bench press and leg extension strength and time to exhaustion during cycle ergometry

Hendrix, CR, Housh, TJ, Mielke, M, Zuniga, JM, Camic, CL, Johnson, GO, Schmidt, RJ, and Housh, DJ. Acute effects of a caffeine-containing supplement on bench press and leg extension strength and time to exhaustion during cycle ergometry. J Strength Cond Res 24(3): 859-865, 2010-The purpose of the present study was to examine the acute effects of a caffeine-containing supplement (SUPP) on 1 repetition maximum (1RM) bench press and leg extension strength, as well as time to exhaustion (TTE), during cycle ergometry at a power output that corresponded to 80% of &OV0312;o2peak. The study used a double-blinded, placebo-controlled, crossover design. Twenty-one untrained men (mean ± SD age = 23.0 ± 2.6 yr) were randomly assigned to take either the SUPP or placebo (PLAC) first. The SUPP contained 400 mg of caffeine, 66.7 mg of capsicum extract, 10 mg of bioperine, and 40 mg of niacin, and the PLAC was microcrystalline cellulose. Sixty minutes after taking either the SUPP or PLAC, the subjects were tested for 1RM bench press and leg extension strength, as well as TTE. After 1 week of rest, the subjects ingested the opposite substance (SUPP or PLAC) and were retested for 1RM bench press and leg extension strength, as well as TTE. The results indicated that the SUPP had no effect on 1RM bench press strength, 1RM leg extension strength, or TTE at 80% &OV0312;o2peak. These findings did not support the use of the caffeine-containing SUPP in the present study as an ergogenic aid in untrained individuals.

Electromyographic and mechanomyographic responses across repeated maximal isometric and concentric muscle actions of the leg extensors

The purpose of the present study was to examine the patterns of responses for torque, electromyographic (EMG) amplitude, EMG mean power frequency (MPF), mechanomyographic (MMG) amplitude, and MMG MPF across 30 repeated maximal isometric (ISO) and concentric (CON) muscle actions of the leg extensors. Twelve female subjects (21.1±1.4yrs; 63.3±7.4kg) performed ISO and CON fatigue protocols with EMG and MMG signals recorded from the vastus lateralis. The relationships for torque, EMG amplitude, EMG MPF, MMG amplitude, and MMG MPF versus repetition number were examined using polynomial regression. The results indicated there were decreases (p<0.05) across the ISO muscle actions for torque (r(2)=0.95), EMG amplitude (R(2)=0.44), EMG MPF (r(2)=0.62), and MMG MPF (r(2)=0.48), but no change in MMG amplitude (r(2)=0.07). In addition, there were decreases across the CON muscle actions for torque (R(2)=0.97), EMG amplitude (R(2)=0.46), EMG MPF (R(2)=0.86), MMG amplitude (R(2)=0.44), and MMG MPF (R(2)=0.80). Thus, the current findings suggested that the mechanisms of fatigue and motor control strategies used to modulate torque production were similar between maximal ISO and CON muscle actions.

The effects of skinfold thicknesses and innervation zone on the mechanomyographic signal during cycle ergometry

The purpose of this study was to examine the effects of skinfold (SF) thicknesses at four locations on the vastus lateralis (VL) muscle and the placement of accelerometers relative to the innervation zone (IZ) on the mechanomyographic (MMG) amplitude and mean power frequency (MPF) responses during incremental cycle ergometry. Twenty adults (age±SD=23.8±3.0 years) participated in the investigation. The MMG signals were detected during incremental cycle ergometry using four accelerometers placed on the right VL. Prior to the cycle ergometer test, SF thicknesses were measured. Simple linear regression analyses and one-way repeated measures analyses of variance (ANOVAs) were performed. The present study found that only 10% of the regression analyses and mean comparisons were significant (p<0.05). Furthermore, the accelerometer placed at the most proximal site (Prox 2) had significantly greater MMG amplitude and MMG MPF than accelerometers placed at more distal sites (Prox 1, Over IZ, and Dist). There were no significant differences, however, in SF thickness between accelerometer placement sites. In addition, the IZ had no effect on MMG amplitude and little effect on MMG MPF values. The results of the present study indicated that the SF thickness values and IZ did not affect the MMG signal.

The influence of the muscle fiber pennation angle and innervation zone on the identification of neuromuscular fatigue during cycle ergometry

The purpose of the present investigation was to compare the electromyographic (EMG) responses and the estimated physical working capacity at the fatigue threshold (PWC(FT)) values recorded from electrode arrangements placed: (1) parallel to the muscle fiber pennation angle (MFPA), (2) parallel to the long axis of the femur, and (3) over the innervation zone (IZ) during incremental cycle ergometry. Thirteen college-aged males and females (mean age ± SD=22.4 ± 3.4 years) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the MFPA and location of the IZ of the vastus lateralis (VL). For determination of the PWC(FT) values, EMG signals were recorded from three bipolar electrode arrangements at different locations over the VL. The results of a one-way repeated measures ANOVA indicated there were no significant (p<0.05) mean differences in PWC(FT) values among the electrode arrangements (parallel to the MFPA=190 ± 36 W; parallel to the long axis of the femur=194 ± 40 W; and over the IZ=199 ± 51 W) or the EMG amplitude and MPF values at the common power outputs. There were also significant correlations (r=0.75-0.91) among the three electrode arrangements for PWC(FT) values. These findings suggested that the PWC(FT), like absolute EMG amplitude and MPF, is robust to the influence of electrode placement over the IZ as well as the orientation with respect to the MFPA during cycle ergometry.

Influences of Body-Size Variables on Age-Related Increases in Isokinetic Peak Torque in Young Wrestlers

Camic, CL, Housh, TJ, Weir, JP, Zuniga, JM, Hendrix, CR, Mielke, M, Johnson, GO, Housh, DJ, and Schmidt, RJ. Influences of body-size variables on age-related increases in isokinetic peak torque in young wrestlers. J Strength Cond Res 24(9): 2358-2365, 2010-The purposes of the present study were to determine the patterns of age-related changes in 1) height (HT), body weight (BW), fat-free weight (FFW), and absolute isokinetic peak torque (PT); and 2) isokinetic PT covaried separately for HT, BW, FFW, and HT and BW combined in young wrestlers. One hundred twenty-five male wrestlers (mean age ± SD = 14.3 ± 2.4 yr; range = 11.1-18.2 yr) volunteered to perform concentric, isokinetic leg extension and flexion at 180°·s−1 on a Cybex II dynamometer to measure PT as well as underwater weighing to determine FFW. The polynomial regression analyses indicated there were significant quadratic increases across age for HT (R2 = 0.62), BW (R2 = 0.56), and FFW (R2 = 0.47). For leg extension, there were significant increases across age for absolute PT (quadratic, R2 = 0.66), PT covaried for HT (linear, r2 = 0.10), PT covaried for BW (linear, r2 = 0.12), PT covaried for FFW (quadratic, R2 = 0.32), and PT covaried for HT and BW combined (quadratic, R2 = 0.11). For leg flexion, there were significant increases across age for absolute PT (linear, r2 = 0.59), PT covaried for HT (linear, r2 = 0.07), PT covaried for BW (linear, r2 = 0.08), PT covaried for FFW (quadratic, R2 = 0.23), and PT covaried for BW and HT combined (linear, r2 = 0.03). The results of this study indicated that age-related increases in leg-extension and flexion PT for the current sample of young wrestlers could not be accounted for by changes in HT, BW, FFW, or HT and BW combined. These findings suggested that neural maturation may contribute to increases in leg strength across age in young wrestlers.

A mechanomyographic frequency-based fatigue threshold test.

UNLABELLED Theoretically, the mechanomyographic (MMG) mean power frequency fatigue threshold (MMG MPF(FT)) describes the maximal isometric torque that can be maintained for an extended period of time with no change in the global firing rate of the unfused, activated motor units. PURPOSE The purposes of this study were twofold: (1) to determine if the mathematical model for estimating the electromyographic (EMG) MPF(FT) from the frequency of the EMG signal was applicable to the frequency domain of the MMG signal to estimate a new fatigue threshold called the MMG MPF(FT); and (2) to compare the mean torque levels derived from the MMG MPF(FT) test for the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles during isometric leg extension muscle actions. METHODS Nine adults (4 men and 5 women; mean+/-S.D. age=21.6+/-1.2 years) performed three or four continuous, fatiguing, isometric muscle actions of the leg extensors at 30, 45, 60, and 75% of maximum voluntary isometric contraction (MVIC) to exhaustion. Surface MMG signals were recorded from the VL, VM, and RF muscles during each fatiguing isometric muscle action. The MMG MPF(FT) was defined as the y-intercept of the isometric torque versus slope coefficient (MMG MPF versus time) plot. RESULTS There were no significant differences among the MMG MPF(FT) values for the VL, VM, and RF (34.8+/-23.4, 32.1+/-16.1, and 31.6+/-15.2 Nm, respectively) muscles. CONCLUSION The MMG MPF(FT) test may provide a non-invasive method to examine the effects of various interventions on the global motor unit firing rate during isometric muscle actions.

The effects of polyethylene glycosylated creatine supplementation on muscular strength and power.

Camic, CL, Hendrix, CR, Housh, TJ, Zuniga, JM, Mielke, M, Johnson, GO, Schmidt, RJ, and Housh, DJ. The effects of polyethylene glycosylated creatine supplementation on muscular strength and power. J Strength Cond Res 24(12): 3343-3351, 2010-The purpose of the present investigation was to examine the effects of 28 days of polyethylene glycosylated creatine (PEG-creatine) supplementation on 1-repetition maximum bench press (1RMBP) and leg extension (1RMLE), mean power (MP), and peak power (PP) from the Wingate Anaerobic test and body weight (BW). This study used a randomized, double-blind, placebo-controlled, parallel design. Twenty-two untrained men (mean age ± SD = 22.1 ± 2.1 years) were randomly assigned to either a Creatine (n = 10) or Placebo (n = 12) group. The Creatine group ingested PEG-creatine (5 g·d−1), whereas the Placebo group ingested maltodextrin powder (5 g·d−1). All subjects performed bench press and bilateral leg extension exercises to determine their 1RM values, and 2 consecutive Wingate Anaerobic Tests (separated by 7 minutes) on a cycle ergometer to determine MP and PP before supplementation (day 0) and after 7 (day 7) and 28 (day 28) days of supplementation. The results indicated that there was a significant (p < 0.05) increase in 1RMBP between days 0 and 28 for the Creatine group but not for the Placebo group. There were no significant changes, however, in 1RMLE, MP, PP, or BW for the Creatine or Placebo group. These findings indicated that 28 days of PEG-creatine supplementation without resistance training increased upper body strength but not lower body strength or muscular power. These findings supported the use of the PEG-creatine supplement for increasing 1RMBP strength in untrained individuals.

Plasma ammonia concentrations and the slow component of oxygen uptake kinetics during cycle ergometry.

Malek, MH, Housh, TJ, Crouch, LD, Johnson, GO, Hendrix, CR, Beck, TW, Mielke, M, Schmidt, RJ, and Housh, DJ. Plasma ammonia concentrations and the slow component of oxygen uptake kinetics during cycle ergometry. J Strength Cond Res 22(6): 2018-2026, 2008-The purposes of this study were to 1) compare the patterns of responses for plasma ammonia concentration ([NH3]) during moderate- vs. heavy-intensity cycle ergometry, and 2) examine the relationship between the &OV0312;o2 slow component (&OV0312;o2SC) and plasma [NH3]. Thirteen healthy, untrained men (mean ± SEM age = 24.8 ± 0.6 years) performed a total of eight constant power output exercises (7 minutes in duration) at two different intensities (moderate, 60% gas exchange threshold [GET] = 60% of the gas exchange threshold; and heavy, Δ50% = 50% of the difference between GET and &OV0312;o2max). Blood was collected from an antecubital vein before the exercise, during the last 3 minutes of the 6-minute warm-up, and during each minute of the 7-minute constant power output workbout. The time course of changes in plasma [NH3] and &OV0312;o2 during the two constant power output exercise intensities were assessed separately using 2 (intensity) × 7 (time) repeated-measures analyses of variance. For 60% GET, there were no significant differences in the mean normalized plasma [NH3] during the 7-minute workbout. For Δ50%, there was a significant increase in the mean normalized plasma [NH3] during the 7-minute workbout. These findings suggest a potential relationship between exercise-induced hyperammonemia and the &OV0312;o2SC during heavy-intensity exercise.