Physiological Adaptations to Taper in Competitive Distance Runners

Abstract

Little is known about the physiological response to taper in distance runners. The aim of this study was to examine the effects of a 3-wk taper (progressive reduction in training volume with no change in intensity) on performance and physiology of competitive distance runners. We implemented a 'whole body to gene' approach to study seven collegiate distance runners (20 ± 1 yr, 66 ± 1 kg) before and after taper. The primary measures included 8-km cross country race performance, gastrocnemius single muscle fiber size and function (peak force, shortening velocity, and power), resting and run-induced gene expression 4 hrs after a standardized 8-km indoor track run [pre-30:18 (min:sec), post-30:20], citrate synthase activity, and maximal and submaximal cardiovascular physiology (Vo2, VE, HR, and RER) before and after taper. The taper was successful at enhancing cross country race performance (-3%, P<0.05). MHC IIa fiber diameter (+7%, P<0.05), force (+11%, P=0.06), and absolute power (+9%, P<0.05) were elevated following taper. In addition to the MHC IIa fiber adaptations, taper elicited a distinct post-run gene response. Specifically, the induction of MuRF-1 was attenuated following taper, whereas MRF-4, HSP 72, and MT-2A displayed an exaggerated response to the standardized run (P<0.05). No changes were observed in MHC I size/function, resting gene expression, citrate synthase activity, or cardiovascular function. Our findings show that tapered training in competitive runners promoted MHC IIa fiber remodeling and a differential transcriptional response following the same exercise perturbation, while having no adverse effects on aerobic physiology. These data suggest that myocellular remodeling is a key ingredient for taper induced gains in running performance.