Fuel for the work required: a practical approach to amalgamating train-low paradigms for endurance athletes

Abstract

Using an amalgamation of previously studied "train-low" paradigms, we tested the effects of reduced carbohydrate (CHO) but high leucine availability on cell-signaling responses associated with exercise-induced regulation of mitochondrial biogenesis and muscle protein synthesis (MPS). In a repeated-measures crossover design, 11 males completed an exhaustive cycling protocol with high CHO availability before, during, and after exercise (HIGH) or alternatively, low CHO but high protein (leucine enriched) availability (LOW + LEU). Muscle glycogen was different (P < 0.05) pre-exercise (HIGH: 583 ± 158, LOW + LEU: 271 ± 85 mmol kg(-1) dw) but decreased (P < 0.05) to comparable levels at exhaustion (≈100 mmol kg(-1) dw). Despite differences (P < 0.05) in exercise capacity (HIGH: 158 ± 29, LOW + LEU: 100 ± 17 min), exercise induced (P < 0.05) comparable AMPKα2 (3-4-fold) activity, PGC-1α (13-fold), p53 (2-fold), Tfam (1.5-fold), SIRT1 (1.5-fold), Atrogin 1 (2-fold), and MuRF1 (5-fold) gene expression at 3 h post-exercise. Exhaustive exercise suppressed p70S6K activity to comparable levels immediately post-exercise (≈20 fmol min(-1) mg(-1)). Despite elevated leucine availability post-exercise, p70S6K activity remained suppressed (P < 0.05) 3 h post-exercise in LOW + LEU (28 ± 14 fmol min(-1) mg(-1)), whereas muscle glycogen resynthesis (40 mmol kg(-1) dw h(-1)) was associated with elevated (P < 0.05) p70S6K activity in HIGH (53 ± 30 fmol min(-1) mg(-1)). We conclude: (1) CHO restriction before and during exercise induces "work-efficient" mitochondrial-related cell signaling but; (2) post-exercise CHO and energy restriction maintains p70S6K activity at basal levels despite feeding leucine-enriched protein. Our data support the practical concept of "fuelling for the work required" as a potential strategy for which to amalgamate train-low paradigms into periodized training programs.

Keywords: Mitochondrial biogenesis; muscle glycogen; train‐low.

Figure 1

Schematic overview of the experimental protocol. On the evening of day 1, subjects completed a glycogen depleting protocol followed by 3 h of best practice recovery nutrition (HIGH) or sleep‐low (LOW + LEU). Throughout the entirety of day 2, subjects consumed a high CHO diet (HIGH) or alternatively, a low CHO and low energy dietary protocol (LOW + LEU) that was matched for both protein and fat intake. During the main experimental trial on day 3, subjects performed an exhaustive cycling protocol in conditions of best practice nutrition (HIGH) in which high CHO intakes were consumed before, during, and after exercise. In contrast, in the LOW + LEU trial, subjects consumed leucine‐enriched protein only. In this way, the LOW + LEU trial represented 3 days of an amalgamation of train‐low strategies consisting of sleep low (day 1), low dietary CHO intake (day 2), and omission of CHO intake before, during, and after exercise (day 3). Muscle biopsies were obtained immediately pre‐exercise, at the point of exhaustion (Exh) and at 3 h post‐exhaustion. *denotes leucine‐enriched protein.

Figure 2

(A) Skeletal muscle glycogen content, (B) Exercise capacity (reflective of set work protocol plus time to exhaustion). *P < 0.05, significant main effect of condition. ^# P < 0.05, significant effect of exercise.

Figure 3

(A) Heart rate response during exercise and plasma (B) Lactate, (C) Glucose, (D) NEFA, (E) Glycerol, (F) β‐hydroxybutyrate, before, during, and after exercise. (G) Carbohydrate oxidation and (H) Lipid oxidation during exercise. *P < 0.05, significant main effect of condition. Shaded area represents exercise duration.

Figure 4

(A) AMPK α2 activity pre‐, post‐, and 3 h post‐exercise. Shaded area represents exercise duration. (B) PCG‐1α, (C) p53, (D), SIRT1, (E) COXIV, and (F) Tfam mRNA pre‐ and 3 h post‐exercise. *P < 0.05, significant main effect of condition, ^# P < 0.05, significant main effect of exercise.

Figure 5

(A) Leucine, (B) BCAAs, and (C) EAAs before, during, and after exercise. Shaded area represents exercise duration. *P < 0.05, significant main effect of condition.

Figure 6

(A) p70S6K, (B) PKB activity, and (C) Serum insulin pre‐, post‐, and 3 h post‐exercise. Shaded area represents exercise duration. *P < 0.05, significant main effect of condition, ^# P < 0.05, significant main effect of exercise.

Figure 7

(A) MuRF1 and (B) Atrogin1 mRNA pre‐ and 3 h post‐exercise. *P < 0.05, significant main effect of condition, ^# P < 0.05, significant main effect of exercise.