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Biomedical subjects

D J Housh

Publications and source records attributed to D J Housh.

At least 19 recordsLinked to original sources
PubMed2001

The effect of mathematical modeling on critical velocity.

The purpose of this investigation was to examine the effects of mathematical modeling on critical velocity (CV) estimates and the oxygen consumption (VO2), heart rate (HR), and plasma lactate values that corresponded to the five CV estimates. Ten male subjects performed a maximal, incremental treadmill test to determine maximal VO2, and four randomly ordered treadmill runs for the estimation of CV. Two linear, two nonlinear, and one exponential mathematical models were used to estimate CV. Regression analyses were used to determine the VO2, HR, and plasma lactate values that corresponded to the five CV estimates from the relationships for VO2, HR, and plasma lactate versus running velocity from the maximal, incremental test. The nonlinear, three-component model (Nonlinear-3) resulted in a mean CV that was significantly (P < 0.05) less than the mean values derived from the other four models, and was the lowest CV estimate for each subject. The percent of maximal VO2, HR, and plasma lactate values that corresponded to the Nonlinear-3 model were 89%, 93%, and 63%, respectively. These findings indicate that CV estimates differ by as much as 20% depending upon the model used to determine the characteristics of the velocity/time relationship. Future studies are needed to determine which model provides the most valid estimate of the demarcation point between heavy and severe exercise.

Adult↗
PubMed2001

The effect of concentric isokinetic strength training of the quadriceps femoris on electromyography and muscle strength in the trained and untrained limb.

The purpose of the present investigation was to examine the effects of unilateral concentric isokinetic leg extension training on peak torque (PT) and electromyographic (EMG) responses in the trained and untrained limbs. Twenty adult men were randomly assigned to a training (TRN, n = 11) or control (CTL, n = 9) group. The TRN group performed 6 sets of 10 leg extensions 3 days per week for 12 weeks at a velocity of 90 degrees.s(-1). All subjects were tested every 4 weeks for PT and EMG responses of both legs at a velocity of 90 degrees.s(-1). The 3-way mixed factorial analysis of variance (ANOVA) indicated a significant (p < 0.05) increase in PT over the 12 weeks in both the trained and untrained limb for the TRN group but no significant change in PT in either limb for the CTL group. The results of the 3-way ANOVA for the EMG data indicated no significant change in EMG amplitude in the trained or untrained limb for the TRN or CTL group. The increase in PT in the absence of a change in EMG may result from hypertrophic factors and/or changes in the other muscles or muscle groups involved in leg extension.

Adaptation, Physiological↗
PubMed2000

The effect of leg extension training on the mean power frequency of the mechanomyographic signal.

The purpose of the present investigation was to examine the effect of concentric isokinetic leg extension training on the mean power frequency (MPF) of the mechanomyographic (MMG) signal. Twenty-one men were assigned into a training (TRN; n = 12) or control (CTL; n = 9) group. The TRN group performed six sets of leg extensions 3 days per week for 12 weeks at a velocity of 90 degrees /s. All subjects were tested every 4 weeks for peak torque (PT), while MMG was recorded from the vastus lateralis. PT increased, but there was no significant (P > 0.05) change in the MMG MPF over the 12-week training period. These results indicate that MMG MPF, measured from the vastus lateralis, was not sensitive to training-induced increases in leg-extension strength, possibly due to competing influences of hypertrophy on the MMG signal and/or training-induced adaptations in muscles other than the vastus lateralis.

Electromyography↗
PubMed2000

Mechanomyographic and electromyographic responses during submaximal cycle ergometry.

The purpose of this study was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses during continuous, cycle ergometer workbouts performed at constant power outputs. Eight adults [mean (SD) age, 21.5 (1.6) years] volunteered to perform an incremental test to exhaustion for the determination of peak power (Wpeak) and four, 15-min (or to exhaustion) rides at constant power outputs of 50%, 65%, 80%, and 95% Wpeak. Piezoelectric crystal contact sensors were placed on the vastus lateralis (VL) and vastus medialis (VM) muscles to record the MMG signals. Bipolar surface electrode arrangements were placed on the VL and VM to record the EMG signals. Five-second samples of the MMG and EMG signals were recorded every 30 s at power outputs of 50%, 65%, and 80% Wpeak, and every 15 s at 95% Wpeak. The amplitudes of the selected portions of the signals were normalized to the first values recorded during the continuous rides, and regression analyses were used to determine whether the slope coefficients for the MMG and EMG versus time relationships were significantly (P < 0.05) different from zero. The results indicate that EMG amplitude increased (range of slope coefficients: 0.03-0.56) during the continuous rides for both muscles at all four power outputs (except the VM at 50% Wpeak), while MMG amplitude increased (slope coefficient at 95% Wpeak for VM = 0.19), decreased (range of slope coefficients for VL and VM at 50% and 65% Wpeak = -0.14 to -0.24), or remained unchanged (range of slope coefficients for VL and VM at 80% Wpeak and VL at 95% peak = -0.06 to 0.12) depending on the power output. The patterns of the MMG responses, however, were similar for the VL and VM muscles, except at 95% Wpeak. Fatigue-induced changes in motor-unit recruitment and discharge rates, or muscular compliance may explain the differences between power outputs in the patterns of the MMG amplitude responses.

Adult↗
PubMed1999

Allometric scaling of isokinetic peak torque: the Nebraska Wrestling Study.

Allometric scaling has been used increasingly in the exercise sciences to control statistically for body size differences in physical performance variables. The purpose of this study was to use multivariate allometric scaling to examine the influence of fat-free mass (FFM) on age-related differences in strength in young club (8-13 years) and high-school (14-18 years) wrestlers. The dependent variables were log-transformed values of isokinetic peak torque for leg extension and flexion at 0.52, 3.14, and 5.24 rad x s(-1)(30, 180, and 300 x s(-1)). The independent variables used in the multiple regression analyses were log-transformed values for FFM, age, and the FFM versus age interaction. The resulting regression equations were of the form: log Y = log a + b1 log X1 + b2 log X2 + bn log Xn. The initial multiple regression analyses showed significant interaction effects (P < 0.05) for all dependent variables, therefore separate regression analyses were performed for the younger and older groups of wrestlers. The results indicate that for the younger wrestlers there were increases in isokinetic peak torque at all velocities across age after controlling for FFM. The FFM scaling exponents ranged from 0.94 to 1.31. All exponents included 1.0 in the 95% confidence interval, except for extension at 3.14 rad x s(-1). For the high-school wrestlers, both FFM and age were significant for the extension data, but only FFM was significant for the flexion data. All FFM exponents included 1.0 in the 95% confidence interval. These results indicate that the relationship between FFM and peak torque differed across age. In addition, with the exception of the flexion data for the high-school wrestlers, within each group increases in isokinetic peak torque occurred across age, independent of increases in FFM. The causes of the age effect for strength are speculative, but it may be due to developmental changes in neuromuscular function, alterations in the distribution of muscle mass as a percentage of FFM and/or the distribution of FFM across body segments.

Adolescent↗
PubMed1997

Validity of near-infrared interactance for estimating relative body fat in female high school gymnasts.

The present investigation examined the validity of near-infrared interactance (NIR) estimates of relative body fat (% fat) from the Futrex-5000 (F5000), Futrex-5000A (F5000 A), and Futrex-1000 (F1000) instruments. Ninety-eight female high school gymnasts (X age+/-SD = 15.7+/-1.2 yr) participated in this investigation. Subsamples were used to cross-validate the F5000 (n = 52), F5000A (n = 46), and F1000 (n = 89) instruments. The NIR % fat estimates were validated against criterion % fat from underwater weighing (UWW) using the adult conversion constants of Brozek et al. (6) (UWWB) and the female age-specific constants of Lohman (23) (UWWL). The cross-validation statistical analysis included examination of the constant error (CE), standard error of estimate (SEE), r, and total error (TE). In addition, full-model multiple regression analyses were used to predict UWWB or UWWL from body weight (BW) and height (HT). BW and HT were correlated with % fat at R = 0.65-0.70, while the validity coefficients for the NIR instruments ranged from r = 0.40-0.78. The F5000 resulted in nonsignificant CE values (-0.3 % fat vs UWWB and 1.5 % fat vs UWWL; p > 0.008) as well as the lowest TE values (TE = 3.1 % fat vs UWWB and 4.0 % fat vs UWWL). All other NIR estimates of % fat resulted in TE values > or = 6.3 % fat. In addition, for all NIR instruments there were negative correlations for the plots of the CE versus the mean of predicted and criterion (UWWB and UWWL) % fat. Therefore, the present findings indicated that the F5000 provided more accurate estimates of % fat than the F5000A or F1000 instruments, but may underestimate the desired minimal body weight for female gymnasts at the low end of the % fat distribution.

Adipose Tissue↗
PubMed1997

Validity of bioelectrical impedence equations for estimating fat-free weight in high school female gymnasts.

The present study examined the validity of bioelectrical impedence (BIA) equations for estimating fat-free weight (FFW) in female gymnasts by comparing the values to those obtained from underwater weighing (UWW). Ninety-seven female Caucasian high school gymnasts (mean age +/- SD = 15.7 +/- 1.1 yr) participated in the study. FFW from UWW was calculated from percent fat using the revised formula of Brozek et al. (mean FFW +/- SD = 43.8 +/- 4.5 kg) and the age-specific constants of Lohman (mean FFW +/- SD = 44.8 +/- 4.6 kg). Cross-validation analyses included examination of the constant error (CE), SEE, r, and total error (TE). The results indicated similar trends between equations when based on either the Brozek or Lohman conversions; however, the CE, SEE, and TE values were consistently lower for the majority of the equations using the revised formula of Brozek et al. Based upon the results of the cross-validation analyses, the equation of Houtkooper et al. and the interlaboratory equations of Van Loan et al. and Lohman, which resulted in identical TE values of 2.4 kg are recommended for use with young high school gymnasts.

Adolescent↗
PubMed1997

The effect of unilateral concentric weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit.

Changes in strength following concentric-only weight training and detraining are poorly understood. The purpose of this investigation was to examine the effects of unilateral concentric leg extension weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit (individual limb strength > bilateral strength/2). Sixteen males volunteered to be subjects for this investigation (concentric training group, N = 8; control group, N = 8). The training group performed 8 weeks of training with the nondominant limb three times per week (3-5 sets X six repetitions), followed by 8 weeks of detraining. These subjects were tested pretraining, posttraining, and following detraining for maximal isometric strength at three joint angles (15, 45, and 75 degrees) in both limbs as well as for the one repetition maximum (1-RM) concentric strength of the trained limb, untrained limb, and bilaterally. The results of this investigation indicated that the effects of the concentric weight training were not joint angle specific as the isometric strength increases occurred at all three joint angles. This effect was found in both limbs, indicating that cross-training occurred. The results of the 1-RM analyses showed that initially there was a bilateral deficit (untrained limb > bilateral, trained limb at pretraining). While the concentric training resulted in increases in 1-RM strength in the trained limb, untrained limb, and bilaterally, differences between bilateral strength and the untrained limb were reversed posttraining and the trained limb values exceeded both the bilateral and untrained limb values. Finally, the effects of detraining were more pronounced for isometric strength vs. 1-RM strength as there was a significant decrease from posttraining in the isometric scores, but the detraining 1-RM values were not significantly decreased from posttraining for either limb or bilaterally.

Adult↗
PubMed1996

Effects of eccentric-only resistance training and detraining.

The purposes of this investigation were to examine the effects of unilateral eccentric-only dynamic constant external resistance (DCER) training of the leg extensor muscles on: (a) eccentric DCER strength in the trained and untrained limbs, (b) concentric isokinetic leg extension peak torque-velocity curves in the trained and untrained limbs, and (c) retention of eccentric DCER strength and concentric isokinetic peak torque in the trained and untrained limbs following detraining. Seventeen adult male (X age +/- SD = 24 +/- 3 yr) volunteers comprised training (TR, n = 9) and control (CTL, n = 8) groups. The TR group trained the leg extensor muscles of the nondominant limb with eccentric-only DCER exercise (3 - 5 sets of 6 repetitions at 80% of the eccentric one-repetition maximum [1-RM] load) for eight weeks followed by eight additional weeks of detraining. The CTL group did not train. All subjects were tested pretraining, posttraining, and after detraining for 1-RM unilateral eccentric DCER strength of the leg extensor muscles as well as concentric isokinetic leg extension peak torque at 1.05, 2.09, 3.14, 4.19, and 5.24 rad.s(-1) in both limbs. Mixed factorial ANOVAs, follow-ups, and post-hoc analyses indicated that the training resulted in increased eccentric DCER strength in both the trained (29 %) and untrained (17 %) limbs, but no change in isokinetic peak torque at any of the velocities of contraction in either limb. Furthermore, the training-induced increases in eccentric DCER strength for both limbs were retained across eight weeks of detraining.

Adult↗
PubMed1996

Effects of unilateral concentric-only dynamic constant external resistance training.

The purposes of this investigation were to examine the effects of unilateral concentric-only leg extension dynamic constant external resistance (DCER) training on: (a) concentric DCER strength in the trained and contralateral (untrained) legs, (b) concentric isokinetic peak torque-velocity curves in the trained and contralateral legs, and (c) retention of concentric DCER strength and concentric isokinetic peak torque in the trained and contralateral legs following detraining. Sixteen adult male (mean age +/- SD = 24.0 +/- 4.0 yr) volunteers comprised training (TR, n = 8) and control (CTL, n = 8) groups. The TR group trained the nondominant limb with concentric-only leg extension DCER exercise (3-5 sets of 6 repetitions at 80% of one-repetition maximum load) for eight weeks followed by eight additional weeks of detraining. The CTL group did not train. All subjects were tested pretraining, posttraining and detraining for unilateral concentric-only leg extension DCER strength as well as concentric isokinetic peak torque at 1.05, 2.09, 3.14, 4.19, and 5.24 rad.s-1 in both legs. Mixed factorial ANOVAs, follow-up, and post-hoc analyses indicated that the training resulted in increased DCER strength in both the trained (42%) and contralateral (15%) legs as well as isokinetic peak torque in the trained leg (7-19%) at velocities ranging from 1.05 to 5.24 rad.s-1. There was no cross-training effect, however, for isokinetic peak torque. Furthermore, the training-induced increases in DCER strength and isokinetic peak torque were retained across eight weeks of detraining.

Adult↗
PubMed1996

Age, fat-free weight, and isokinetic peak torque in high school female gymnasts.

The purpose of this study was to examine the covariate influence of fat-free weight (FFW) on age-related increases in isokinetic peak torque for leg flexion and extension in high school female gymnasts. Seventy-two gymnasts (X age +/- SD = 15 7 +/- 1.2 yr) volunteered to be measured for isokinetic leg flexion and extension strength using a calibrated Cybex II dynamometer at 30, 180, and 300 degrees*s(-1) as well as for body composition from underwater weighing. The results indicated that there were significant (P < 0.05) zero-order correlations for age versus leg flexion (r = 0.36-0.47) and extension (r = 0.51-0.57) peak torque, as well as FFW versus leg flexion (r = 0.50-0.66) and extension (r = 0.620.73) peak torque. There were also significant (P < 0.05) first-order partial correlations between age and peak torque (covaried for FFW) for leg extension at 30 (r = 0.25), 180 (r = 0.36-0.39), and 300 degrees*s(-1) (r = 0.25-0.28) but not for leg flexion. These findings indicated that for the high school female gymnasts in the present study, there were age-related increases in strength that could not be accounted for by changes in FFW. It is possible that factors such as an increase in muscle mass per unit of FFW and/or neural maturation contribute to strength increases during adolescence in female athletes.

Adolescent↗
PubMed1996

Validity of skinfold estimates of percent fat in high school female gymnasts.

A preseason estimation of body composition may be useful for assigning a safe minimal body weight for female gymnasts. The present investigation examined the validity of 11 skinfold equations for predicting percent body fat (%fat) in high school female gymnasts (X age +/- SD = 15.7 +/- 1.2 yr) by comparing the values with those obtained from underwater weighing. Seventy-three gymnasts (X %fat +/- SD = 18.6 +/- 4.5%fat) volunteered to serve as subjects. The statistical analyses included examination of the constant error (CE), standard error of estimate (SEE), correlation coefficient (r), and total error (TE). The results of this investigation indicated that 7 of the 11 equations resulted in TE values that were < or = 3.9%fat (range, 3.3-3.9%fat). Of these, the quadratic sum-of-three skinfold equation of Thorland et al. (37) satisfies the most cross-validation criteria and, therefore, is recommended for estimating body composition and minimal body weight in high school female gymnasts. The other six equations with TE values of < or = 3.9%fat should be considered acceptable alternatives.

Adipose Tissue↗
PubMed1996

Neuromuscular fatigue thresholds of the vastus lateralis, vastus medialis and rectus femoris muscles.

The purpose of this study was to compare the power outputs associated with the onset of neuromuscular fatigue in the superficial muscles of the quadriceps femoris group by simultaneously monitoring the EMG activity from the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles during a Physical Working Capacity at the Fatigue Threshold (PWCFT) test. Eleven adult males (mean +/- SD = 24 +/- 3y) served as subjects. There were no significant (p > 0.05) differences among the mean PWCFT values for the VL (226 +/- 58 W), VM (223 +/- 58 W) and RF (203 +/- 54 W) muscles. These findings indicates that the superficial muscles of the quadriceps femoris group generally responded as a unit with respect to the onset (threshold) of neuromuscular fatigue as measured by the PWCFT test.

Adult↗
PubMed1995

Electromyographic fatigue thresholds of the superficial muscles of the quadriceps femoris.

The purpose of this investigation was to compare the thresholds of neuromuscular fatigue determined simultaneously from the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles using the electromyographic fatigue threshold (EMGFT) test. Eight adult volunteers [mean (SD) age, 33 (10) years] served as subjects for this investigation. The results of a one-way repeated measured ANOVA indicated that there was a significant (P < 0.05) difference among the mean EMGFT values for the VL [248(31)W], VM [223(43)W] and RF [220(30)W] muscles. Tukey post-hoc comparisons indicated that the EMGFT for the RF was significantly (P < 0.05) lower than that of the VL. These findings suggested that during cycle ergometry there is a dissociation in neuromuscular fatigue characteristics of the superficial muscles of the quadriceps femoris group.

Adult↗
PubMed1995

The effect of unilateral eccentric weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit.

Eccentric resistance training is an important component of many rehabilitation protocols. The adaptations following eccentric training are poorly understood in relation to concentric training. The purpose of this investigation was to examine the effects of unilateral eccentric leg extension weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit. Seventeen males volunteered to be subjects for this investigation and were divided into an eccentric training group (N = 9) and a control group (N = 8). The eccentric group performed 8 weeks of unilateral eccentric weight training with the nondominant limb three times per week (3-5 sets of six repetitions) followed by 8 weeks of detraining. These subjects were tested pretraining, posttraining, and following detraining for maximal isometric strength at three joint angles (15, 45, and 75 degrees) in both limbs as well as for the one-repetition maximum (1-RM) eccentric strength of the trained limb, untrained limb, and bilaterally. The results of this investigation indicated that the effects of the eccentric weight training were joint angle specific [significant increases at 45 and 75 degrees (p < 0.05)]. This effect was found in both limbs, indicating a cross-training effect that was joint angle specific. The results from the 1-RM analyses indicated that the bilateral deficit exists for eccentric contractions (untrained limb > bilateral at pretraining) and that unilateral eccentric training increases this effect (trained and untrained limbs > bilateral posttraining); however, the unilateral training also resulted in increased bilateral strength. Both the 1-RM and isometric analyses showed that the training effects persisted over 8 weeks of detraining.

Adult↗
PubMed1995

Anthropometric estimation of thigh muscle cross-sectional area.

The purpose of this investigation was to derive and validate circumference and skinfold equations for estimating the anatomical cross-sectional area (CSA) of the quadriceps, hamstrings, and total thigh muscles. Forty-three adult male (mean age +/- SD = 25 +/- 5 yr) volunteers underwent magnetic resonance imaging (MRI) to determine the CSA of the thigh muscles at the midfemur level as well as midthigh circumference and anterior thigh skinfold assessment. Multiple regression analyses were used to derive equations for predicting quadriceps, hamstrings, and total thigh muscle CSA of the dominant limb from the anthropometric dimensions on a random sample of 30 of the subjects. Cross-validation (CV) analyses were performed for each equation on: (a) the nondominant thigh of the derivation group (N = 30); (b) the dominant thigh of the CV group (N = 13); and (c) the nondominant thigh of the CV group (N = 13). The CV total error values for the quadriceps, hamstrings, and total thigh muscle CSA ranged from 5.4 to 14.4, 3.3 to 5.5, and 10.0 to 25.4 cm2, respectively. The anthropometric equations are recommended for one-time estimates of muscle CSA values in healthy, well-nourished young adult males when more sophisticated procedures are not available.

Adult↗
PubMed1995

Validity of skinfold equations for estimating body density in youth wrestlers.

The present investigation examined the validity of 16 skinfold equations for predicting body density (BD) in youth wrestlers (mean age +/- SD = 11.0 +/- 1.3 yr) by comparing the values to those obtained from underwater weighing. Forty-eight members of youth wrestling clubs (mean BD +/- SD = 1.0634 +/- 0.0125 g.cm-3) volunteered to serve as subjects. The statistical analyses included examination of the constant error (CE), standard error of estimate (SEE), correlation coefficient (r), and total error (TE). The results of this investigation indicated that all of the equations resulted in TE values that were > or = 0.0106 g.cm-3 (range = 0.0106-0.0229 g.cm-3) which corresponded to > or = 4.9% body fat. The TE values were too large to provide accurate estimates of body composition in the present sample of youth wrestlers. Future studies should use the CE values from the present investigation to adjust the intercepts of the skinfold equations in the present study and cross-validate the modified equations on young male athletes.

Body Composition↗