Single Muscle Fiber Gene Expression with Run Taper

Abstract

This study evaluated gene expression changes in gastrocnemius slow-twitch myosin heavy chain I (MHC I) and fast-twitch (MHC IIa) muscle fibers of collegiate cross-country runners (n = 6, 20±1 y, VO2max = 70±1 ml•kg−1•min−1) during two distinct training phases. In a controlled environment, runners performed identical 8 kilometer runs (30∶18±0∶30 min:s, 89±1% HRmax) while in heavy training (∼72 km/wk) and following a 3 wk taper. Training volume during the taper leading into peak competition was reduced ∼50% which resulted in improved race times and greater cross-section and improved function of MHC IIa fibers. Single muscle fibers were isolated from pre and 4 hour post run biopsies in heavily trained and tapered states to examine the dynamic acute exercise response of the growth-related genes Fibroblast growth factor-inducible 14 (FN14), Myostatin (MSTN), Heat shock protein 72 (HSP72), Muscle ring-finger protein-1 (MURF1), Myogenic factor 6 (MRF4), and Insulin-like growth factor 1 (IGF1) via qPCR. FN14 increased 4.3-fold in MHC IIa fibers with exercise in the tapered state (P<0.05). MSTN was suppressed with exercise in both fiber types and training states (P<0.05) while MURF1 and HSP72 responded to running in MHC IIa and I fibers, respectively, regardless of training state (P<0.05). Robust induction of FN14 (previously shown to strongly correlate with hypertrophy) and greater overall transcriptional flexibility with exercise in the tapered state provides an initial molecular basis for fast-twitch muscle fiber performance gains previously observed after taper in competitive endurance athletes.

Fiber Type-Specific Satellite Cell Content in Cyclists Following Heavy Training with Carbohydrate and Carbohydrate-Protein Supplementation

“…Consistent with the idea that MyHC IIa fibers are especially sensitive to heavy training, MyHC IIa fibers undergo substantial remodeling when provided with a period of recovery (Trappe et al, 2000, 2006; Neary et al, 2003; Luden et al, 2010). More specific to the myogenic program, the induction of FN14 mRNA following running exercise was suppressed in MyHC IIa muscle fibers relative to the response elicited after 3 weeks of tapered training (Murach et al, 2014). This is relevant here because FN14 and the associated TWEAK pathway have been implicated in the regulation of myogenesis (Enwere et al, 2012, 2014).…”

Less Is More: The Physiological Basis for Tapering in Endurance, Strength, and Power Athletes

“…Since that time, taper's efficacy has been well documented in swimming, cycling, running, triathlon, rowing, strength training, and team sports to name a few. The effects of tapering are apparent from the whole body (macro) [4] to the cell and gene (micro) [5,6] levels and even include psychological improvements [7]. Despite the multitude of data supporting taper's effectiveness, some athletes and coaches still fail to acknowledge its importance and implement the practice.…”

“…However, the literature indicates that fitness in endurance athletes (measured as aerobic capacity, or VO2max) is not lost following the taper period and five studies have actually shown an increase in fitness with less training [18,[21][22][23]25]. Reducing training volume for as long as four weeks [7] by >85% (in the last week) [6,19] still yields gains in performance without a loss of fitness. Considering the robust adaptations observed with short-duration high-intensity interval training, even in already highly trained individuals [26,27], it should come as no surprise that a well-designed taper of reduced volume and quality high intensity work can preserve fitness for up to a month.…”

“…Improved fast-twitch fiber function may allow for a harder "push" to the finish line or improve economy (faster speed with the same amount of effort). It has recently been shown that favorable regulation of molecular hypertrophy markers, specifically in fast-twitch fibers, may support the high rate of growth in these fibers with tapering [6]. Although taper has a positive effect down to the molecular level, taper-mediated growth is only realized when volume is adequately reduced [11].…”

“…To our knowledge, data on the mechanisms of performance enhancement with tapering in strength or power athletes are not available at the muscle cell level. However, strength and power training can selectively hypertrophy fast-twitch muscle fibers [6], potentially maximizing growth adaptation before tapering ensues. Thus, tapering likely augments performance in intermittent-type athletes by a different mechanism than in endurance athletes.…”