The effect of infrared radiation emitting garments on acute skeletal muscle adaptive responses

The formation of new components of the mitochondrial reticulum (mitochondrial biogenesis) and the growth of new capillaries (angiogenesis) are important adaptive responses to endurance exercise training. Endurance exercise elicits a range of homeostatic disturbances that, when detected, stimulate acute molecular signalling cascades for mitochondrial biogenesis and angiogenesis. Augmenting the activation of these signalling cascades or prolonging their activation may enhance the adaptative potential. Various interventions are used in an attempt to increase acute adaptive signalling. Infrared radiation (IR) is one such intervention. IR radiators may augment aspects of acute adaptive signalling cascades in vitro and in murine models in vivo. However, IR delivery using emitters is impractical. Therefore, IR emitting fabric (IREF) is a novel, simple and more easily accessible method for IR radiation delivery. It is, however, unclear if IR emitted by IREF may augment molecular signalling cascades in vitro. Moreover, the effect of IREF on acute molecular signalling in humans is unknown. Therefore, the purpose of this thesis was to examine the effect of IREF on acute mitochondrial biogenic and angiogenic signalling cascades in C2C12 myotubes and in humans at rest and following exercise.

Chapter 4 investigated the effect of IREF on acute mitochondrial biogenesis and angiogenesis cell signalling cascades in C2C12 myotubes over a 48-hour time course. There was no change to acute markers of angiogenesis (eNOS and VEGF) over the 48-hour time course (P > 0.05). CaMKII phosphorylation and PGC-1α mRNA expression were inhibited in IREF compared to CON after 48 hours. A reduction of these signals suggests mitochondrial biogenesis was inhibited by IREF exposure in C2C12 myotubes.

Chapter 5 investigated the effect of IREF on muscle oxygenation and skin blood flow in the human forearm. There was no change in either parameter following up to 90-minutes of wear in IREF compared to SHAM.

Chapter 6 investigated the effect of IREF on acute mitochondrial biogenesis and angiogenesis signalling cascades in humans over a 3-hour time course at rest. There were no changes in protein phosphorylation (AMPK, CaMKII, p38 MAPK and eNOS) or mRNA expression (PGC-1α and VEGF) in either IREF or SHAM.

Chapter 7 investigated the effect of IREF on acute mitochondrial biogenesis and angiogenesis signalling cascades in human skeletal muscle tissue following high intensity interval exercise (HIIE). IREF increased CaMKII phosphorylation post-exercise above that seen in SHAM in both cytosolic and nuclear fractions and p38 MAPK phosphorylation increased post-exercise in IREF only in the cytosolic fraction of skeletal muscle. Moreover, there was a tendency toward an increased PGC-1α mRNA expression in IREF compared to SHAM post-exercise. Additionally, there was an increase in NRF1, p53 and VEGF mRNA expression post exercise in IREF compared to SHAM.

The key novel findings of this thesis were: 1) IREF inhibited mitochondrial biogenesis in C2C12 myotubes; 2) IREF did not alter skin blood flow or muscle oxygenation in the human forearm at rest; 3) IREF did not alter acute mitochondrial biogenic or angiogenic signalling cascades in humans at rest over a 3-hour time course; 4) IREF augmented mitochondrial biogenic and angiogenic signalling cascades in humans following HIIE. Collectively, these findings provide novel insights into the efficacy of IREF to augment acute adaptive signalling in vitro and, most importantly, in humans at rest and following HIIE.