Differential transcriptional activation of select metabolic genes in response to variations in exercise intensity and duration.

Cellular adaptations to endurance training are influenced by the intensity and duration of exercise. To examine the impact of exercise intensity and duration on the acute transcriptional regulation of metabolic genes in red (RG) and white (WG) gastrocnemius muscle, rats completed either low-intensity [ approximately 50% maximal O2 uptake (VO2 max)] treadmill exercise (LIE) for 45 min, LIE for 180 min, or high-intensity ( approximately 75% VO2 max) exercise (HIE) for 45 min. LIE for 45 min activated (P < 0.05) transcription of the pyruvate dehydrogenase kinase-4 (PDK4), uncoupling protein-3 (UCP3), heme oxygenase-1 (HO-1), and hexokinase II (HK II) genes in RG within 1 h after exercise. In WG, transcription of PDK4, UCP3, HKII, and lipoprotein lipase (LPL) was also induced, whereas transcription of the HO-1 gene did not change. In RG, extending LIE duration from 45 to 180 min elicited a similar activation of PDK4 and UCP3 ( approximately 15-fold) but a far greater increase in HO-1 (>30-fold) and HKII transcription (>25-fold). In WG, extending LIE for 180 min induced a much greater and prolonged (through 2- to 4-h recovery) activation of PDK4, UCP3 (both >200-fold), and HO-1 (>10-fold). HIE elicited a similar pattern of gene activation to LIE in both RG and WG, with the exception that HIE triggered >10-fold activation of HO-1 in WG. These data provide evidence that both the intensity and the duration of exercise affect the transcriptional regulation of metabolic genes in muscle in a fiber type-specific manner, possibly reflecting the relative stress imposed by the exercise bout.