Submitted on October 28, 2006
Accepted on June 18, 2007
DO SKELETAL MUSCLE PHENOTYPIC CHARACTERISTICS OF XHOSA AND CAUCASIAN ENDURANCE RUNNERS DIFFER WHEN MATCHED FOR TRAINING AND RACING DISTANCES?
Tertius Abraham Kohn1, Birgitta Essen-Gustavsson2, and Kathryn Helen Myburgh3*
1 Physiological Sciences, University of Stellenbosch, Matieland, Western Cape, South Africa
2 Department of Large Animal Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden
3 Physiological Sciences, Stellenbosch University, MATIELAND, South Africa
* To whom correspondence should be addressed. E-mail: khm{at}sun.ac.za.
Although East African black athletes dominate endurance running events, it is unknown whether black and white endurance runners with similar racing ability, matched for training, may differ in their skeletal muscle biochemical phenotype. Thirteen Xhosa (XR) and 13 Caucasian (CR) endurance runners were recruited and matched for 10 km performance, average preferred racing distance (PRDA) and training volume. Sub-maximal and maximal exercise tests were done and Vastus lateralis muscle biopsies were taken. XR were significantly lighter and shorter than CR athletes, but had similar maximum oxygen consumption corrected for body weight and peak treadmill speed (PTS). XR had lower plasma lactate concentrations at 80% PTS (P < 0.05) compared to CR. Also, XR had more type IIA (42.4 ± 9.2 vs. 31.3 ± 11.5%, P < 0.05) and less type I fibers (47.8 ± 10.9 vs. 63.1 ± 13.2%, P < 0.05), although oxidative enzyme acitvites did not differ. Furthermore, XR compared to CR had higher lactate dehydrogenase (LDH) activity in homogenate muscle samples (383 ± 99 vs. 229 ± 85 µmol/min/g dry weight, P < 0.05), and in both type IIa (P < 0.05) and type I (P = 0.05) single fiber pools. A marked difference (P < 0.05) in the composition of LDH isoform content was found between the two groups with XR having higher levels of LDH5-4 isoforms (LDH-M) than CR, which was not accounted for by fiber type differences alone. These results confirm differences in muscle phenotype and physiological characteristics, particularly associated with high intensity running.
