Six weeks of a polarized training-intensity distribution leads to greater physiological and performance adaptations than a threshold model in trained cyclists

• Published in: Journal of applied physiology (1985) Vol. 114; no. 4; pp. 461 - 471
• Main Authors: Neal, Craig M, Hunter, Angus M, Brennan, Lorraine, O'Sullivan, Aifric, Hamilton, D Lee, De Vito, Giuseppe, Galloway, Stuart D R
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 15.02.2013
• Subjects: Adaptation; Adaptation, Physiological; Adult; Athletes; Bicycling; Biomarkers - urine; Biopsy; Cross-Over Studies; Discriminant Analysis; Exercise; Exercise Test; Human performance; Humans; Least-Squares Analysis; Magnetic Resonance Spectroscopy; Male; Metabolomics - methods; Mitochondria, Muscle - metabolism; Monocarboxylic Acid Transporters - metabolism; Muscle Contraction; Muscle Fatigue; Muscle Proteins - metabolism; Muscle Strength; Muscle, Skeletal - metabolism; Muscle, Skeletal - physiology; Physical Endurance; Scotland; Sports training; Symporters - metabolism; Time Factors; Urinalysis; Scotland
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00652.2012

This study was undertaken to investigate physiological adaptation with two endurance-training periods differing in intensity distribution. In a randomized crossover fashion, separated by 4 wk of detraining, 12 male cyclists completed two 6-wk training periods: 1) a polarized model [6.4 (±1.4 SD) h/wk; 80%, 0%, and 20% of training time in low-, moderate-, and high-intensity zones, respectively]; and 2) a threshold model [7.5 (±2.0 SD) h/wk; 57%, 43%, and 0% training-intensity distribution]. Before and after each training period, following 2 days of diet and exercise control, fasted skeletal muscle biopsies were obtained for mitochondrial enzyme activity and monocarboxylate transporter (MCT) 1 and 4 expression, and morning first-void urine samples were collected for NMR spectroscopy-based metabolomics analysis. Endurance performance (40-km time trial), incremental exercise, peak power output (PPO), and high-intensity exercise capacity (95% maximal work rate to exhaustion) were also assessed. Endurance performance, PPOs, lactate threshold (LT), MCT4, and high-intensity exercise capacity all increased over both training periods. Improvements were greater following polarized rather than threshold for PPO [mean (±SE) change of 8 (±2)% vs. 3 (±1)%, P < 0.05], LT [9 (±3)% vs. 2 (±4)%, P < 0.05], and high-intensity exercise capacity [85 (±14)% vs. 37 (±14)%, P < 0.05]. No changes in mitochondrial enzyme activities or MCT1 were observed following training. A significant multilevel, partial least squares-discriminant analysis model was obtained for the threshold model but not the polarized model in the metabolomics analysis. A polarized training distribution results in greater systemic adaptation over 6 wk in already well-trained cyclists. Markers of muscle metabolic adaptation are largely unchanged, but metabolomics markers suggest different cellular metabolic stress that requires further investigation.