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Biomedical subjects

G O Johnson

Publications and source records attributed to G O Johnson.

89 records · Page 5Linked to original sources
PubMed1984

Validity of anthropometric equations for the estimation of body density in adolescent athletes.

One hundred forty-one adolescent male (age: X +/- SD = 17.43 +/- 0.96 yr) and 133 adolescent female (16.51 +/- 1.39 yr) athletes were studied to determine the validity of available anthropometric equations for estimating body density (BD). Anthropometric measures were taken of eight skinfolds, nine circumferences, and four diameters. Body density, determined by underwater weighing (corrected for residual lung volume), was 1.080 +/- 0.010 g X ml-1 for the males and 1.066 +/- 0.010 g X ml-1 for the females. Cross-validation of 17 selected equations on the males revealed validity coefficients ranging from R2 = 0.29-0.67 and total-error scores ranging from 0.0062-0.0277 g X ml-1. Among the females, cross-validation of 15 selected equations revealed validity coefficients ranging from R2 = 0.31-0.67 and total-error scores ranging from 0.0064-0.0214 g X ml-1. While equations of either linear or quadratic form demonstrated acceptable accuracy in the estimation of male BD values, only quadratic equations displayed similar levels of accuracy among the females. Based on these results, as well as consideration of characteristics related to inter-tester error and the variance of predicted scores, the quadratic equations of Jackson and Pollock, Lohman, and Pollock et al., as well as the linear equation of Forsyth and Sinning, were found to be particularly appropriate for the estimation of BD in adolescent athletes.

Adipose Tissue↗
PubMed1981

Body composition and somatotype characteristics of junior Olympic athletes.

Body composition and somatotype were determined in Junior Olympic competitors to evaluate the structural characteristics concomitant to high proficiency in various athletic activities. Underwater weighings and anthropometric determinations of somatotype were performed on 145 male and 133 female adolescent participants in national meet competition in the sports of track and field, gymnastics, diving, and wrestling. The most frequent differences within either the male or female Junior Olympic samples involved the performers in throwing events (shot put, discus, and javelin), who were taller, heavier, fatter, and of unique somatotype when compared to all or most other competitors. Additional structural differences, generally of a lesser magnitude, also existed between other groups of Junior Olympians. Differences in body composition characteristics were also noted when Junior Olympians were compared with other adolescent athletes or non-athletes.

Adolescent↗
PubMedDate not supplied

Effects of muscle-strength training on the functional status of patients with osteoarthritis of the knee joint.

This study was designed to determine whether an 8-week isokinetic muscle-strength-training program improved the functional health status of patients with osteoarthritis of the knee joint. Twenty volunteers with osteoarthritis of the knee joint were randomly assigned to either an experimental (n=10) or control (n=10) group. The experimental group completed six sets of five maximal contractions three times per week for 8 weeks on a Cybex II dynamometer at 90 degrees per second. Both groups were pre- and posttest for extension and flexion strength of the right and left legs, the 50-foot walk time, range of motion at the knee joint, the Osteoarthritis Screening Index (OASI), and the Arthritis Impact Measurement Scale (AIMS). There was a significant decrease in pain and stiffness, and a significant increase in mobility. There was also a significant decline in arthritis activity in the experimental group as measured by the OASI and AIMS. The experimental group significantly increased in all strength measures, while the control group increased in only right leg flexion and left leg extension across the training period.

Activities of Daily Living↗
PubMedDate not supplied

Weight control for high school wrestlers.

Anthropometric measurements were obtained from 141 Nebraska State Tournament wrestlers in order to predict their ideal minimum wrestling weight via the Tipton-Tcheng predictim equation. An r of .93 was found between predicted weight and actual weight for 131 of the state tournament qualifiers (excluding heavy-weights). Data indicated that the winners more nearly approximated their predicted weight than did the losers. The mean percent difference between actual weight showed that the upper weight classes (138- 185) more closely approximated their predicted weight than the lower weight than the lower weight classes (98-132). The results indicate that a prediction equation can reliably predict a wrestlers ideal weight and could be used to eliminate unwise weight reduction practices.

Adolescent↗
PubMedDate not supplied

The effects of leg angular velocity on mean power frequency and amplitude of the mechanomyographic signal.

The purpose of the present investigation was to examine the effects of leg angular velocity on the mean power frequency (MPF) and amplitude of the mechanomyographic (MMG) signal during maximal concentric (CON) isokinetic muscle actions. Sixteen adult subjects performed maximal CON leg extensions on a calibrated Cybex 6000 dynamometer at leg angular velocities of 60 and 300 degrees.s-1. MMG was detected by a piezoelectric crystal contact sensor placed over the mid-portion of the vastus lateralis muscle. The results indicated a significant (p < 0.05) velocity-related decrease in peak torque (PT) and increase in MMG amplitude from 60 to 300 degrees.s-1. There was, however, no velocity-related change (p > 0.05) in MMG MPF. These findings did not support our hypothesis that increases across velocity in MMG amplitude were due to decreases in muscle stiffness as a result of a shift in the contribution of slow and fast-twitch muscle fibers to PT production. Future research should examine the potential influence of actin-myosin cycling rate as well as limb movement on the MPF and amplitude of the MMG signal.

Actins↗
PubMedDate not supplied

Mechanomyographic responses to continuous, constant power output cycle ergometry.

PURPOSE: The purpose of the present investigation was to examine the mechanomyographic (MMG) and electromyographic (EMG) responses to continuous, constant power output cycle ergometer workbouts. METHODS: Eight adult male volunteers (mean age +/- SD = 22 +/- 2 yrs) performed three continuous, one-hour workbouts at 28, 35, and 42% of peak power (Ppeak). RESULTS: The slope coefficients for the mean normalized MMG amplitude versus time relationships were significantly (p < 0.05) less than zero, while the slope coefficients for the mean normalized EMG amplitude versus time relationships were significantly (p < 0.05) greater than zero. CONCLUSION: The results indicated dissociation between the patterns of the mechanical (MMG) and electrical (EMG) activity of the vastus lateralis during continuous cycle ergometry at low power outputs. The increases in EMG amplitude were likely due to the recruitment of additional motor units. The decreases in MMG amplitude across time may have been due to the phenomenon known as "muscular wisdom" and/or decreases in muscular compliance.

Adult↗
PubMedDate not supplied

Cross-correlation analyses of mechanomyographic signals from the superficial quadriceps femoris muscles during concentric and eccentric isokinetic muscle actions.

The purpose of this investigation was to examine the cross-correlation coefficients of mechanomyographic (MMG) signals recorded from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles during maximal, concentric and eccentric isokinetic muscle actions. Eleven females (mean +/- SD age = 21 +/- 1 yr) performed such muscle actions of the leg extensors at 60 degrees.s-1 on a Cybex 6000 dynamometer. MMG signals were sampled simultaneously from the VL, RF, and VM at 1000 Hz by piezoelectric crystal contact sensors. Peak composite cross-correlation coefficients (rxy) and common variances (rxy2) were determined for each between-muscle comparison (VL vs. RF, VL vs. VM, and RF vs. VM). The results indicated peak cross-correlation coefficients ranging from rxy = 0.38 to 0.52, while common variances (rxy2) between signals ranged from 14% to 27% across all time lags (tau = -50...). In conjunction with other studies, these results suggested that despite the potential for some cross-talk, MMG measurements can be used to examine differences between the patterns of MMG amplitude and frequency responses of the superficial quadriceps femoris muscles.

Adult↗
PubMedDate not supplied

Mechanomyographic and electromyographic amplitude and frequency responses during fatiguing isokinetic muscle actions of the biceps brachii.

The purpose of this investigation was to examine the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) patterns during fatiguing isokinetic muscle actions of the biceps brachii. Ten adults [three women (mean +/- SD age = 20 +/- 2 yrs) and seven men (mean +/- SD age = 23 +/- 3 yrs) ] volunteered to perform 50 consecutive maximal, concentric isokinetic muscle actions of the biceps brachii at 180 degrees x s(-1). The percent decline (mean +/- SD) in isokinetic peak torque (PT) was 70 +/- 17% and polynomial regression analyses indicated a cubic relationship (R2 = 0.994) between PT and repetition number. Both MMG amplitude and MMG MPF decreased linearly (r2 = 0. 774 and 0.238, respectively) across repetitions. The results for EMG amplitude demonstrated a cubic (R2 = 0.707) pattern across repetitions, where EMG amplitude increased during repetitions 1-20, remained stable during repetitions 20-40, and increased during repetitions 40-50. There was a quadratic (R2 = 0. 939) reduction in EMG MPF throughout the test. The decreases in MMG amplitude and MMG MPF may have been due to de-recruitment of fast fatiguing motor units, a reduction in muscular compliance, or the effects of "muscle wisdom." The results for EMG amplitude may have reflected nonmaximal efforts by the subjects and/or peripheral fatigue. The factor(s) determining the decrease in EMG MPF are unclear, although a reduction in muscle fiber action potential conduction velocity may have been partially responsible.

Adult↗