Biomedical subjects

Daniel A Hernandez

Publications and source records attributed to Daniel A Hernandez.

4 recordsLinked to original sources

PubMed2005

A comparison of isoload and isoinertial leg press training on bone and muscle outcomes.

The subjects of this study (n = 20; 16 women, 4 men) performed 10 weeks of leg press training using one of two exercise modes (isoload or isotonic) with no crossover. Their workouts, which were performed 3 times per week, involved 4 sets of 8 repetitions with maximal voluntary effort. Testing was performed pre- and posttraining to examine bone and muscle changes. Posttraining, both groups incurred significant concentric knee extensor strength and leg muscle mass gains, while the percentage of body fat and total body fat mass each decreased. Leg and total body bone mineral densities showed group-by-time interactions, as isoload exercise caused posttraining gains, while isoinertial values were unchanged. Bone resorption assays showed insignificant changes. Isoload training likely involved greater strain magnitudes and rates to evoke higher peak forces and osteogenesis. Transduction of the training stimulus may have involved (a) formation in response to microdamage, and (b) piezoelectric-induced potentials that stimulated site-specific osteoblast activity and osteogenesis.

Absorptiometry, Photon↗

PubMed2005

Metabolic responses to the seated calf press exercise performed against inertial resistance.

INTRODUCTION: Future in-flight strength training devices may use inertial resistance to abate mass and strength losses to muscle groups such as the triceps surae, which incurs pronounced deficits from space travel. Yet little data exist regarding physiological outcomes to triceps surae exercise performed against inertial resistance. Two sets of subjects were employed to note either blood lactate (La-) or net caloric cost responses to seated calf presses done on an inertial resistance ergometer. METHODS: Both sets of subjects performed 3 identical 3-set 10-repetition workouts. Blood La- measurements were made pre- and 5 min post-exercise. During workouts, breath-by-breath O2 uptake values were also recorded to help determine the net caloric cost of exercise. RESULTS: Compared to pre-exercise (mean +/- SEM) blood La- (2.01 +/- 0.08 mmol x L(-1)) values, post-exercise (4.73 +/- 0.24 mmol x L(-1)) measurements showed a significant increase. Delta (post/pre differences) La- correlated significantly (r = 0.31-0.34) to several workout performance measures. Net caloric cost averaged 52.82 +/- 3.26 kcals for workouts; multivariate regression showed a subject's height, body mass, and body surface area described the variance associated with energy expenditure. CONCLUSIONS: Workouts evoked minimal energy expenditure, though anaerobic glycolysis likely played a major role in ATP resynthesis. Metabolic and exercise performance measures were likely influenced by series elastic element involvement of the triceps surae-Achilles tendon complex. Ergometer calf presses provided a high-intensity workout stimulus with a minimal metabolic cost.

Aerospace Medicine↗

PubMed2003

Inclusion of eccentric actions on net caloric cost resulting from isoinertial resistance exercise.

Net O(2) uptake was measured from maximal-effort 3-set, 8-repetition seated leg press protocols on an isoinertial ergometer. Subjects (25 women, 9 men) did 2 workouts each exerting concentric-eccentric (CE) and concentric-only (CO) knee extensor forces to measure work and net caloric cost. Significant (p < 0.05) relationships between work and net caloric cost resulted from CE and CO workouts for the male, female, and total subject sample. Two-way repeated-measures analyses of variance showed CE workouts resulted in significantly higher work but not net caloric cost and values. CE workouts likely relied on the knee extensors series elastic element to perform an additional approximately 3,600 J of eccentric work at no additional net caloric cost. Unlike other exercise modes, maximal-effort eccentric actions on the isoinertial ergometer, as done in the current study, provide no additional net caloric cost and is thus safe to administer to populations in whom metabolic cost is a concern.

Adult↗

PubMed2003

A multivariate approach to predicting knee extensor performance.

The impact of two predictor variables (estimated knee extensor fast-twitch fiber percentage, body mass) on performance measures (vertical jump power output, leg press peak angular velocity) were examined. Subjects (25 men, 27 women) performed 5 workouts involving 2 vertical jump, leg press, and 50-repetition isokinetic tests (to estimate knee extensor fast-twitch fiber percentage). Multivariate regression determined the following significant (p < 0.05) vertical jump equations: predicted male power output = -59.3464 + 1.566 (estimated knee extensor fast-twitch muscle fiber percent) + 15.7884 (body mass), predicted female power output = 36.1574 + 3.4248 (estimated knee extensor fast-twitch muscle fiber percent) + 9.8633 (body mass). Leg press peak angular velocity equations were insignificant by gender; thus, pooled data yielded the following: predicted leg press peak angular velocity = 18.6187 + 0.235 (estimated knee extensor fast-twitch muscle fiber percent) + 0.3801 (body mass). Body mass explained more variance for each performance measure.

Adult↗