Stéphane P. Dufour

Effect of interval versus continuous training on cardiorespiratory and mitochondrial functions: relationship to aerobic performance improvements in sedentary subjects

The goal of the study was to determine the effects of continuous (CT) vs. intermittent (IT) training yielding identical mechanical work and training duration on skeletal muscle and cardiorespiratory adaptations in sedentary subjects. Eleven subjects (6 men and 5 women, 45 +/- 3 years) were randomly assigned to either of the two 8-wk training programs in a cross-over design, separated by 12 wk of detraining. Maximal oxygen uptake (Vo2max) increased after both trainings (9% with CT vs. 15% with IT), whereas only IT was associated with faster Vo2 kinetics (tau: 68.0 +/- 1.6 vs. 54.9 +/- 0.7 s, P < 0.05) measured during a test to exhaustion (TTE) and with improvements in maximal cardiac output (Qmax, from 18.1 +/- 1.1 to 20.1 +/- 1.2 l/min; P < 0.01). Skeletal muscle mitochondrial oxidative capacities (Vmax) were only increased after IT (3.3 +/- 0.4 before and 4.5 +/- 0.6 micromol O2 x min(-1) x g dw(-1) after training; P < 0.05), whereas capillary density increased after both trainings, with a two-fold higher enhancement after CT (+21 +/- 1% for IT and +40 +/- 3% after CT, P < 0.05). The gain of Vmax was correlated with the gain of TTE and the gain of Vo2max with IT. The gain of Qmax was also correlated with the gain of VO2max. These results suggest that fluctuations of workload and oxygen uptake during training sessions, rather than exercise duration or global energy expenditure, are key factors in improving muscle oxidative capacities. In an integrative view, IT seems optimal in maximizing both peripheral muscle and central cardiorespiratory adaptations, permitting significant functional improvement. These data support the symmorphosis concept in sedentary subjects.

Eccentric Exercise Training: Modalities, Applications and Perspectives

Eccentric (ECC) exercise is classically used to improve muscle strength and power in healthy subjects and athletes. Due to its specific physiological and mechanical properties, there is an increasing interest in employing ECC muscle work for rehabilitation and clinical purposes. Nowadays, ECC muscle actions can be generated using various exercise modalities that target small or large muscle masses with minimal or no muscle damage or pain. The most interesting feature of ECC muscle actions is to combine high muscle force with a low energy cost (typically 4- to 5-times lower than concentric muscle work) when measured during leg cycle ergometry at a similar mechanical power output. Therefore, if caution is taken to minimize the occurrence of muscle damage, ECC muscle exercise can be proposed not only to athletes and healthy subjects, but also to individuals with moderately to severely limited exercise capacity, with the ultimate goal being to improve their functional capacity and quality of life. The first part of this review article describes the available exercise modalities to generate ECC muscle work, including strength and conditioning exercises using the body’s weight and/or additional external loads, classical isotonic or isokinetic exercises and, in addition, the oldest and newest specifically designed ECC ergometers. The second part highlights the physiological and mechanical properties of ECC muscle actions, such as the well-known higher muscle force-generating capacity and also the often overlooked specific cardiovascular and metabolic responses. This point is particularly emphasized by comparing ECC and concentric muscle work performed at similar mechanical (i.e., cycling mechanical power) or metabolic power (i.e., oxygen uptake,

Effects of exercise and training in hypoxia on antioxidant/pro-oxidant balance

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Erythrocyte-dependent regulation of human skeletal muscle blood flow: role of varied oxyhemoglobin and exercise on nitrite, S-nitrosohemoglobin, and ATP

). In particular, at a similar mechanical power, ECC muscle work induces lower metabolic and cardiovascular responses than concentric muscle work. However, when both exercise modes are performed at a similar level of

Different timing of changes in mitochondrial functions following endurance training.

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Effect of eccentric versus concentric exercise training on mitochondrial function

, a greater cardiovascular stress is observed during ECC muscle work. This observation underlines the need of cautious interpretation of the heart rate values for training load management because the same training heart rate actually elicits a lower