This study examined the change in 15K running performance for master runners over 21 years (1978–1998). Official times were collected for 60 male runners from the same running event. Trends in running performance were analyzed with several models (linear, polynomial, and segmented-line). A self-report questionnaire was used to quantify training and to characterize runners. Peak age of running performance was indirectly estimated at 33 years using a second-degree polynomial. The performance trend was also associated with an inflection point at age 41 directly estimated from a nonlinear, segmented, mixed-effects model (95% confidence interval: 38.77–42.44). After age 41, master runners ran nearly 1 min slower each year. Besides age, other parameters that influenced performance over time included type of training (interval training) and body weight. These data might be among the first to describe the trend in running performance for a group of master athletes, most of whom were noncompetitive runners.
Jill M. Slade, Hector De Los Santos-Posadas and M. Elaine Cress
Jeffrey J. Brault, Theodore F. Towse, Jill M. Slade and Ronald A. Meyer
Short-term creatine supplementation is reported to result in a decreased ratio of phosphocreatine (PCr) to total creatine (TCr) in human skeletal muscle at rest. Assuming equilibrium of the creatine kinase reaction, this decrease in PCr:TCr implies increased cytoplasmic ADP and decreased Gibbs free energy of ATP hydrolysis in muscle, which seems contrary to the reported ergogenic benefits of creatine supplementation. This study measured changes in PCr and TCr in vastus lateralis muscle of adult men (N = 6, 21–35 y old) during and 1 day after 5 d of creatine monohydrate supplementation (0.43 g·kg body weight−1·d−1) using noninvasive 31P and 1H magnetic-resonance spectroscopy (MRS). Plasma and red-blood-cell creatine increased by 10-fold and 2-fold, respectively, by the third day of supplementation. MRS-measured skeletal muscle PCr and TCr increased linearly and in parallel throughout the 5 d, and there was no significant difference in the percentage increase in muscle PCr (11.7% ± 2.3% after 5 d) vs. TCr (14.9% ± 4.1%) at any time point. The results indicate that creatine supplementation does not alter the PCr:TCr ratio, and hence the cytoplasmic Gibbs free energy of ATP hydrolysis, in human skeletal muscle at rest.