SKELETAL-MUSCLE RESPONSE TO SHORT ENDURANCE TRAINING IN HEART-TRANSPLANT RECIPIENTS

Objectives. We sought to examine the effects of endurance training on the ultrastructural characteristics of skeletal muscle in heart transp lant recipients (HTRs) and age-matched control subjects (C). Backgroun d. Deconditioning is one of the factors involved in the peripheral lim itation of exercise capacity of HTRs, and training has proven to be be neficial. Methods. Biopsies of the vastus lateralis muscle, analyzed b y ultrastructural morphometry, and quadriceps muscle cross-sectional a rea, assessed by computed tomography (CT), were performed in 12 HTRs a nd 7 age-matched C before and 6 weeks after an endurance training prog ram. Maximal oxygen uptake (peak (V) over dot O-2,) was determined by an incremental exercise test. Additionally muscle biopsies were perfor med before and after a 6-week control period in four HTRs to check for spontaneous improvement. Results. Training resulted in similar increa ses in peak (V) over dot O-2, (11% in HTRs, 8.5% in C), ventilatory th reshold (23% in HTRs, 32% in C) and total endurance work (54% in HTRs, 31% in C). Volume density of total mitochondria increased significant ly (26% in HTRs, 33% in C) with a predominant increase of subsarcolemm al mitochondrial volume density (74% in HTRs, 70% in C). The capillary /fiber ratio increased by 19% in C only. In the nontrained group, none of the structural markers was spontaneously modified. Conclusions. Si x weeks of endurance training in HTRs and C led to similar improvement s of aerobic work capacity. However, the decreased muscular capillary network in HTRs remained unchanged with training. Immunosuppressive th erapy might be responsible for the discrepancy between the normal mito chondrial content and the reduced capillary supply of these patients. (C) 1998 by the American College of Cardiology.