Biomedical subjects

Brent L. Arnold

Publications and source records attributed to Brent L. Arnold.

3 recordsLinked to original sources

PubMed2003

Creatine Supplementation Increases Total Body Water Without Altering Fluid Distribution.

OBJECTIVE: To examine the effects of oral creatine (Cr) monohydrate supplementation on muscle Cr concentration, body mass, and total body water (TBW), extracellular water (ECW), and intracellular water (ICW) volumes. DESIGN AND SETTING: After an overnight fast, urinary Cr and creatinine concentrations, muscle Cr concentration, body mass, TBW, ECW, and ICW were measured, and subjects were randomly assigned to either a Cr or a placebo (P) group. The Cr group ingested 25 g/d of Cr for 7 days (loading phase) and 5 g/d for the remaining 21 days (maintenance phase), whereas the P group ingested a sucrose P using the same protocol. All the measures were reassessed immediately after the loading and maintenance phases. SUBJECTS: Sixteen men (age = 22.8 +/- 3.01 years, height = 179.8 +/- 7.1 cm, body mass = 84.8 +/- 11.2 kg) and 16 women (age = 21.8 +/- 2.51 years, height = 163.4 +/- 5.9 cm, body mass = 63.6 +/- 14.0 kg) involved in resistance training volunteered to participate in this study. MEASUREMENTS: Muscle Cr concentration was determined from the vastus lateralis muscle using a percutaneous needle-biopsy technique. Total body water, ECW, and ICW volumes were assessed using deuterium oxide and sodium bromide dilution analyses. RESULTS: The Cr group experienced a significant increase in muscle Cr concentration, body mass, and TBW. The P group experienced a small but significant increase in TBW only. CONCLUSIONS: The Cr supplementation protocol was effective for increasing muscle Cr concentrations, body mass, and TBW; however, fluid distribution was not changed.

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PubMed2001

Neuromuscular Response Characteristics in Men and Women After Knee Perturbation in a Single-Leg, Weight-Bearing Stance.

OBJECTIVE: We examined whether muscle response times and activation patterns in the lower extremity differed between men and women in response to a rotational knee perturbation while standing in a single-leg, weight-bearing stance. DESIGN AND SETTING: We used a lower extremity perturbation device to produce a sudden, forward, and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Subjects completed 10 trials of both internal and external rotation perturbation; the first 5 acceptable trials were averaged and used for data analysis. Two separate, repeated-measures analyses of variance were used to compare myoelectric response times and activation patterns between men and women for both internal and external rotation perturbation. SUBJECTS: Thirty-two female (19 lacrosse, 13 soccer) and 32 male (lacrosse) healthy intercollegiate athletes participated in the study. MEASUREMENTS: We used surface electromyography to record long latency reflex times of the medial and lateral quadriceps, hamstring, and gastrocnemius muscles. RESULTS: Women responded faster than men, primarily due to a shorter latency in quadriceps activation. However, men and women exhibited no difference in muscle-recruitment order. CONCLUSIONS: Although men and women demonstrated similar muscle-recruitment patterns to an imposed lower extremity perturbation, women tended to activate their quadriceps earlier than men. Whether this earlier quadriceps activation diminishes the ability of the hamstrings to adequately stabilize the knee joint or subjects the anterior cruciate ligament to greater risk of injury is still unknown and requires further study. Furthermore, although surface electromyography and measurement of myoelectric response times are useful in evaluating the timing, activation order, and coactivity patterns of the knee musculature, future studies should evaluate sex differences across the complete response continuum, including measures of intrinsic muscle stiffness, electromechanical delay, and time to force production.

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PubMed2001

Duration of Maintained Hamstring Flexibility After a One-Time, Modified Hold-Relax Stretching Protocol.

OBJECTIVE: Previous research suggests proprioceptive neuromuscular facilitation (PNF) stretching techniques produce greater increases in range of motion than passive, ballistic, or static stretching methods. The purpose of our study was to measure the duration of maintained hamstring flexibility after a 1-time, modified hold-relax stretching protocol. DESIGN AND SETTING: The study had a 1 x 1 mixed-model, repeated-measures design. The independent variables were group (control and experimental) and time (0, 2, 4, 6, 8, 16, and 32 minutes). The dependent variable was hamstring flexibility as measured in degrees of active knee extension with the hip flexed to 90 degrees. Measurements were taken in a preparatory military academy athletic training room. SUBJECTS: Thirty male subjects (age, 18.8 +/- 0.63 years; height, 185.2 +/- 14.2 cm; weight, 106.8 +/- 15.7 kg) with limited hamstring flexibility in the right lower extremity were randomly assigned to a control (no-stretch) group or an experimental (stretch) group. MEASUREMENTS: All subjects performed 6 warm-up active knee extensions, with the last repetition serving as the prestretch measurement. The experimental group received 5 modified (no-rotation) hold-relax stretches, whereas the control group rested quietly supine on a table for 5 minutes. Posttest measurements were recorded for both groups at 0, 2, 4, 6, 8, 16, and 32 minutes. RESULTS: The repeated-measures analysis of variance revealed a significant group-by-time interaction, a significant main effect for group, and a significant main effect for time. Dunnett post hoc analysis revealed a significant improvement in knee-extension range of motion in the experimental group that lasted 6 minutes after the stretching protocol ended. CONCLUSIONS: Our findings suggest that a sequence of 5 modified hold-relax stretches produced significantly increased hamstring flexibility that lasted 6 minutes after the stretching protocol ended.

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