Training: functional improvements of skeletal muscle oxidative metabolism can occur earlier than the enhancement of mitochondrial biogenesis

Effect of heat acclimation on metabolic adaptations induced by endurance training in soleus rat muscle

“…The decrease of PRK suggests an alteration of the maintenance of mitochondrial quality in response to endurance training. These results are not in accordance with the acute effect of exercise described in other studies (Faure et al, 2016;Zoladz & Grassi, 2015) but our results must be interpreted with caution because we only measured total protein content in whole muscle.…”

“…The skeletal muscle adaptations induced by aerobic training are well known. Muscle mitochondrial content has been shown to increase after endurance training (Holloszy, 1967;Holloszy & Coyle, 1984;Zoladz & Grassi, 2015;Zoll et al, 2003), involving both the size and number of mitochondria (Hoppeler et al, 1973;Morgan et al, 1971). Endurance training may also induce alterations in mitochondrial dynamics.…”

Adaptation of motor unit contractile properties in rat medial gastrocnemius to treadmill endurance training: Relationship to muscle mitochondrial biogenesis

“…As found in the present study, the signals for mitochondrial network reorganization in the MGS ( Fig 6 ) and an increase in PGC-1α content in this part of muscle precede an increase in the mitochondrial electron transport chain proteins content ( Fig 8 ) and mtDNA copy number ( Fig 7 ). Intensified mitochondrial biogenesis after endurance training is one of the most important adaptive responses leading to enhanced muscle energy homeostasis during exercise, as well as resistance to fatigue [ 1 , 4 , 5 , 11 , 16 , 19 ]. The commonly used expression “training-induced increase in mitochondrial biogenesis” is very vague and could be a source of confusion, as argued before [ 12 ].…”

“…Due to the pattern of changes observed in mitochondrial biogenesis markers such as an increase in mitochondrial ETC protein content, the second option appears to be more likely, i.e., training-induced adaptive changes lead to energy saving and enhanced muscle efficiency in the early stages of training before intensification of mitochondrial biogenesis. However, we cannot exclude a possibility that the adaptive neuromuscular changes could result from training-induced enhancement of muscle energy status during exercise, with no involvement of mitochondrial biogenesis-related mechanisms, such as intensification of parallel activation [ 5 , 8 , 12 , 19 ]–known also as each step-activation (ESA) [ 69 ], and/or via an increase in mitochondrial efficiency (an increase in P/O ratio) [ 15 ], allowing the observed improvement in MU function ( Fig 3B ). This rather complex adaptive changes observed in neuromuscular function, including increased fatigue resistance, shortening of the twitch contraction time and increased ability to potentiate force in the early stages of training, is a new observation which requires further study.…”

“…Endurance training enhances muscle performance and resistance to fatigue [ 1 – 5 ]. Prolonged periods of endurance training have been reported to modify the activity and content of proteins associated with ATP usage, such as sarco/endoplasmic reticulum (SR) Ca 2+ -ATPase (SERCA) pumps [ 6 – 8 ], parvalbumin and myosin heavy chain (MyHC) isoforms [ 9 , 10 ] as well as proteins involved in the ATP production system, including electron transport chain proteins in the mitochondria [ 3 , 11 , 12 ].…”