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

Abstract

Aim: To investigate physiological adaptation with two endurance training periods differing in intensity distribution. Methods: In a randomised cross-over fashion, separated by 4-weeks of detraining, 12 male cyclists completed two 6-week training periods: (1) a polarised model (6.4(±1.4)hrs.week(-1); 80%, 0%, 20% of training time in low, moderate and high intensity zones); and (2) a threshold model (7.5(±2.0)hrs.week(-1); 57%, 43%, 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 (MCT1/4) expression, and morning first void urine samples collected for NMR spectroscopy based metabolomics analysis. Endurance performance (40km time trial), incremental exercise, peak power output, and high-intensity exercise capacity (95% Wmax to exhaustion) were also assessed. Results: Endurance performance, peak power output, lactate threshold, MCT4, and high-intensity exercise capacity all increased over both training periods. Improvements were greater following polarised than threshold for peak power output (Mean (±SEM) change of 8(±2)% vs. 3(±1)%, P less than 0.05), lactate threshold (9(±3)% vs. 2(±4)%, P less than 0.05), and high-intensity exercise capacity (85(±14)% vs. 37(±14)%, P less than 0.05). No changes in mitochondrial enzyme activities or MCT1 were observed following training. A significant multi-level partial least squares-discriminant analysis model was obtained for the threshold model but not the polarised model in the metabolomics analysis. Conclusion: A polarised training distribution results in greater systemic adaptation over 6 weeks 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.