Robert A. Lehnhard

Myosin heavy chain profiles and body composition are different in old versus young Standardbred mares.

There are limited data on age-related changes in body composition or skeletal muscle in the horse. Therefore, the purpose of this study was to investigate any differences in muscle myosin heavy chain (MHC) and body composition associated with aging. Twenty-three young (4-8 years) and eight old (20+ years) unfit Standardbred mares were evaluated. Rump fat thickness was measured using B-mode ultrasound and per cent body fat (% fat) was calculated. Needle muscle biopsies were obtained from right gluteus medius muscle. MHC composition was determined via sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Three MHC isoforms were subsequently identified as type I, type IIA, and type IIX and quantified using a scanning and densometric system. There were no significant differences (p>0.05) between old and young mares in fat (%) (19.0+/-6.4 vs 20.5+/-5.4), fat mass (kg) (102.3+/-39.9 vs 106.9+/-37.1), or body weight (kg) (529.4+/-34.9 vs 512.7+/-57.7). However, the old mares had significantly (p<0.05) greater lean body mass than the young mares (427.1+/-24.5 vs 405.7+/-37.9). Aged mares had significantly (p<0.05) less type I (7.8+/-2.9% vs 12.1+/-4.4%) and IIA (27.8+/-7.1% vs 36.1+/-9.5%) fibres than the young group but more type IIX (64.6+/-4.7% vs 51.8+/-11.1%). The MHC data are consistent with the age-related changes seen in other species.

Age, Sex, and Body Mass Index in Performance of Selected Locomotor and Fitness Tasks by Children in Grades K-2

The purpose of this study was to examine the contributions of 3 predictor variables (age, sex, and body mass index) to performance of 7 fundamental movement skills (locomotor; run, gallop, hop, leap, jump, skip, and slide) and 4 fitness tasks (grip strength, step test, sit and reach, and timed sit-ups) by 65 children in Grades K-2 (M =6 yr.). A multiple regression analysis indicated that running, leaping, and skipping improved with age. No sex differences were observed on any of the seven skills. In terms of the four fitness tasks, age was positively associated with timed sit-ups and grip strength and inversely associated with step-test performance. Sex was associated with step-test and sit and reach performance (girls performed better on both). Finally, body mass index was related to increased grip strength and fewer timed sit-ups.

Growth rates in running speed and vertical jumping by boys and girls ages 11-13.

This study examined growth rates in running speed and vertical jump among middle school children. 45 boys and 31 girls ages 11–13 years were tested on running speed and vertical jump three times (September, February, and May) during the school year. Hierarchical linear modeling was used to estimate initial status and growth rates for the entire sample (base model) and the association of running and vertical jump with height, weight, and sex (conditional model). Positive overall growth rates were found for both running speed and vertical jump. Increased height and weight at the time of measurement were not significantly associated with growth rate for running. The growth rate for vertical jump was positively associated with height but unrelated to increased weight. Boys showed steeper growth rates than girls in jumping. No sex differences were found in running speed for either initial status or growth rate. Furthermore, these results suggest highly variable rates of physical maturation but no general period of ‘adolescent awkwardness’.

Grip-Strength Performances by 6- to 19-Yr.-Old Children with and without Hearing Impairments:

86 children and youth enrolled at a residential school for the deaf were matched with 86 children and youth with normal hearing (by age, sex, height, weight, and hand preference) from four public schools. Each participants grip strength was tested with a calibrated hydraulic dynamometer set at the second position. No significant between-group differences were observed. The authors attributed the similar between-group performances to the equal opportunities for participation in sport and physical education in this residential school.

HEALTH-RELATED PHYSICAL FITNESS LEVELS OF ELEMENTARY SCHOOL CHILDREN AGES 5-9

National health goals include an increase in the physical activity and physical fitness of school-age children by the year 2000. To assess current fitness levels in the state of Maine, more than 8,000 public school students, ages five through nine, were assessed using a nationally known (American Alliance for Health, Physical Education, Recreation and Dance) health-related physical fitness test. Maine students were then compared with a national norm group on (1) the one-mile walk/run (minutes:seconds), (2) skinfold thickness (centimeters), (3) one-minute timed sit-ups (number performed correctly), and (4) the sit and reach test for flexibility (centimeters). Generally, Maine boys and girls scored higher than the norms on the sit-up, sit and reach, and one-mile walk/run; however, they had significantly larger skinfold thicknesses. Implications for assessment of health-related fitness in this age group were discussed.

Variations in lactate during a graded exercise test due to sampling location and method

The present study tested the hypothesis that lactate concentration ([La]) would differ between sample sites and between assay techniques that used different analytical substrates. Six clinically normal adult (two Thoroughbreds, three Standardbreds and one Quarter Horse) mares weighing between 435 and 560 kg were used in the study. Each mare performed an incremental exercise test (graded exercise test, GXT) where it ran on a treadmill at a fixed 6% grade. The GXT started at 3 m s for 1 min with increased in speed by 1 m s every 60 s until the horses completed the final 10 m s step. Jugular vein, pulmonary arterial and carotid arterial blood samples (14 ml) were collected before exercise and during the last 10 s of each step of the GXT. [La] was measured in whole blood (WB, no manipulations), total blood (TB, where the red blood cells were lysed) and plasma. Data were used to calculate the velocity to produce [La] of 4 mmol l (VLA4) and 10 mmol l 21 (VLA10). Statistical analysis utilized a three-way ANOVA and, where appropriate, the Holm–Sidak or the Student Neuman–Keuls method for post hoc comparisons. The null hypothesis was rejected when P , 0.05. There was an effect of exercise intensity on [La] for all three methods (P , 0.001) with all means during exercise significantly greater than the resting mean, and there were differences due to method (i.e. analytical substrate) (P , 0.001) and sample site (P 1⁄4 0.043). Comparisons of least-squared means (LSM ^ SE) within site revealed that there was a difference (P , 0.05) between jugular vein (5.41 ^ 0.24) and carotid artery (6.24 ^ 0.24) and between carotid and pulmonary artery (5.98 ^ 0.24). There was no difference (P . 0.05) between jugular vein and pulmonary artery. Within method, there was a difference (P , 0.05) between WB (6.54 ^ 0.36) and TB (5.06 ^ 0.36) and between TB and plasma (6.04 ^ 0.64), but there was no difference (P . 0.05) between WB (6.54 ^ 0.36) and plasma (6.04 ^ 0.64). Further analysis of the data demonstrated that the method and sample site influenced (P , 0.05) VLA4 and VLA10.

Aerobic performance by children in grades 4 to 8: a repeated-measures study.

Aerobic capacity reflects consumption of O2 by working muscles during vigorous physical activity and is an indicator of cardiovascular health. This study examined change in aerobic performance by children in Grades 4 to 8 (Ages= 9–14) over 14 mo. 105 healthy children in a small, rural, middle-class school participated. All were tested five times on the Progressive Aerobic Cardiovascular Endurance Run (PACER) at 8- or 9-wk. intervals during the 2004–2005 school year, with follow-up measurements the next September and December. Hierarchical Linear Modeling applied to analyze the data showed that overall improvement in aerobic performance from September to May was statistically significant as children increased their PACER scores from 26 to 49 laps. These gains were lost over the summer but returned to the original slope by the second follow-up measurement. Regardless of age, sex, Body Mass Index, or sports participation, children followed a similar pattern: steady improvement during the school year, loss of those gains over the summer, and return to the original slope the following year.

Ephedra increases VO2, impairs thermoregulation and cardiovascular function, but does not enhance exercise performance

The dietary supplement ephedra is a potent sympathomimetic that was banned by the US Food and Drug Administration in 2003 because of its deleterious effects on cardiovascular function and thermoregulation during exercise. Unfortunately, extracts of ephedra can still be obtained via the internet and are in use worldwide. The horse is the only athletic species other than humans that sweats to thermoregulate and it controls cardiovascular function in a similar fashion. The purpose of this study was to use the horse to examine the acute effects of ephedra (Ma Huang) to investigate on markers of performance as well as effects on cardiovascular function and thermoregulation during acute exercise. Six Standardbred mares (~450 kg; 6-12 years of age) were used in a crossover design consisting of a ephedra (Ma Huang containing 8% ephedra alkaloid) and control (applesauce) group. All horses performed an incremental graded exercise test (GXT) at a 6% fixed grade to measure oxygen uptake (VO2), run time, velocity at V...

The metabolic response to treadmill graded exercise: traditional vs. underwater

The purpose of this study was to determine the metabolic effect(s) of four graded exercise tests (GXT) performed on the underwater treadmill (UWT), and compare them to the results from performing the standard Bruce protocol on a traditional land treadmill (LT). Twelve male Division I college athletes performed the stand Bruce protocol on a LT and 4 different GXT protocols on the UWT. Each test was performed to volitional max. oxygen consumption (VO2), heart rate (HR), respiratory exchange ratio (RER) and blood lactate (BL), which were measured at regular intervals throughout each of the GXTs. A two-way ANOVA with repeated measures was used to determine any main effect among the variables within the protocols and within the stages. Established effects were identified further using Tukeys post-hoc analysis. VO2 and HR were positively correlated in all the GXTs, (r=0.992−0.999). When comparing the UWT GXTs to the Bruce, significant (P≤0.001) differences were found within certain stages for each of the depen...

The lactate paradox: a review

The phenomenon known as the lactate paradox has been a topic of heated debate since it gained worldwide attention following Operation Everest in the early 1980s. What began as the simple finding that blood lactate (blood [La]) for a given sub-maximal workload or VO2 following acclimatization to high altitude is reduced compared with sea-level values, morphed into a complex set of parameters that have been redefined several times in the nearly 30 years that the lactate paradox has been researched. Though several strong hypotheses have been proposed to, to date, no one hypothesis has been able fully to explain the lactate paradox. The goal of the current article was to bring together the most prominent studies done on the lactate paradox and illuminate the details brought forth by each. In doing so we hope to stimulate new hypotheses and research studies that will further our understanding of the lactate paradox.