Schoepe et al. investigated the effects of a 10-weeks incremental training protocol on rat running on a 10% or 16% incline. Interestingly, the scientists found that only in the 16% incline group marked changes in skeletal muscle size and metabolism occurred, while the 10% incline group stagnated:
Within ten weeks animals trained with 16% incline developed hypertrophy (LVPWD: 1,6±0,1 vs. 2,4±0,1mm; p<0,05) with normal function (Ejection fraction: 75,2±2,5 vs. 75,6±2,1%; n.s.). However, after 6 weeks there was a temporary impairment in contractile function (EF: 74,5±1,67 vs. 65,8±2,3%; p<0,05; eFS%: 44,92±1,53 vs. 38,12±2,04%; p<0,05), which was associated with decreased maximal respiratory capacity of isolated mitochondria (state 3 respiration: 326±71 vs. 161±22 natomsO/min/mg; p<0,05) and a gene expression shift from the adult (α) to the fetal (β) isoform of myosin heavy chain (α MHC: from 1,49±0,27 to 0,62±0,07; p<0,05; β MHC: from 0,38±0,06 to 0,64±0,28; p<0,05). [...] In contrast, at 10% incline, there was no hypertrophy at ten weeks (LVPWD: 1,7±0,1 vs. 1,8±0,1mm; n.s.), normal function (EF: 74,3±1,5 vs. 69,0±1,0%; n.s.; eFS%: 45,3±1,4 vs. 40,0±0,8%; n.s.) and maximal respiratory capacity was normal at all time points.What is of particular interest is the occurrence of a temporary impairment in contractile function, which may well be regarded as a sign of temporary overreaching. This, in turn, appears to be necessary to trigger the muscular adoption the visible (and mostly desired) outcome of which is skeletal muscle hypertrophy.