Superior mitochondrial adaptations in human skeletal muscle after interval compared to continuous single‐leg cycling matched for total work

Abstract

We employed counterweighted single-leg cycling as a unique model to investigate the role of exercise intensity in human skeletal muscle remodelling. Ten young active men performed unilateral graded-exercise tests to measure single-leg V̇O2, peak and peak power (W ). Each leg was randomly assigned to complete six sessions of high-intensity interval training (HIIT) [4 × (5 min at 65% W and 2.5 min at 20% W )] or moderate-intensity continuous training (MICT) (30 min at 50% W ), which were performed 10 min apart on each day, in an alternating order. The work performed per session was matched for MICT (143 ± 8.4 kJ) and HIIT (144 ± 8.5 kJ, P > 0.05). Post-training, citrate synthase (CS) maximal activity (10.2 ± 0.8 vs. 8.4 ± 0.9 mmol kg protein min ) and mass-specific [pmol O •(s•mg wet weight) ] oxidative phosphorylation capacities (complex I: 23.4 ± 3.2 vs. 17.1 ± 2.8; complexes I and II: 58.2 ± 7.5 vs. 42.2 ± 5.3) were greater in HIIT relative to MICT (interaction effects, P < 0.05); however, mitochondrial function [i.e. pmol O •(s•CS maximal activity) ] measured under various conditions was unaffected by training (P > 0.05). In whole muscle, the protein content of COXIV (24%), NDUFA9 (11%) and mitofusin 2 (MFN2) (16%) increased similarly across groups (training effects, P < 0.05). Cytochrome c oxidase subunit IV (COXIV) and NADH:ubiquinone oxidoreductase subunit A9 (NDUFA9) were more abundant in type I than type II fibres (P < 0.05) but training did not increase the content of COXIV, NDUFA9 or MFN2 in either fibre type (P > 0.05). Single-leg V̇O2, peak was also unaffected by training (P > 0.05). In summary, single-leg cycling performed in an interval compared to a continuous manner elicited superior mitochondrial adaptations in human skeletal muscle despite equal total work.

Preservation of skeletal muscle mitochondrial content in older adults: relationship between mitochondria, fibre type and high‐intensity exercise training

“…Each single fibre was fibre‐typed using the dot blotting method (MacInnis et al . ). Briefly a PVDF membrane was activated in 96% ethanol for 120 s and equilibrated in transfer buffer for 120 s. Following this, 1 μl (10%) of each fibre was spotted on the PVDF membrane.…”

“…; MacInnis et al . ). Briefly, denatured protein in the whole muscle samples and calibration curve samples were separated on 26 well, 10% or 4–15% Criterion TGX Stain‐Free gels (Bio‐Rad, Hercules, CA, USA) and run for 45 min at 200 V. The total protein loaded was visualised using UV activation of the gel and analysed with Image Lab 5.2.1 (Bio‐Rad).…”

“…Segments of single fibres were collected from either fresh muscle or freeze‐dried muscle, as previously described (Murphy, ; MacInnis et al . ; Wyckelsma et al . ) and placed in 10 μl of 3× SDS denaturing solution (0.125 m Tris‐HCI, 10% glycerol, 4% SDS, 4 m urea, 10% 2‐mercaptoethanol and 0.001% Bromophenol Blue, pH 6.8, diluted 2:1 with 1× Tris .…”

“…High‐intensity interval training (HIT) is superior in upregulating mitochondrial content in healthy young adults compared to moderate‐intensity exercise (MacInnis et al . ) but its effectiveness in older adults is unknown.…”

Enhanced Protein Translation Underlies Improved Metabolic and Physical Adaptations to Different Exercise Training Modes in Young and Old Humans

“…Combined training (CT) offers many benefits of both aerobic and resistance training, although the intensity of aerobic and resistance components are lower than either HIIT or standard RT programs (Irving et al, 2015). Lower exercise intensity may limit training adaptations (Ross et al, 2015), particularly of mitochondria (MacInnis et al, 2016). A comprehensive approach to different exercise programs and the specific physiological and molecular adaptations and the potential impact of age on these adaptations remain to be determined.…”