Intensity-controlled treadmill running in rats: VO2max and cardiac hypertrophy

Physiological studies of long-term cardiovascular adaptation to exercise re quire training regimens that give robust conditioning effects and adequate testing procedures to quantify the outcome. We developed a valid and reprod ucible protocol for measuring maximal oxygen uptake ((V) over dotO(2max)), which was reached at a 25 degrees inclination with a respiratory exchange r atio > 1.05 and blood lactate > 6 mmol/l. The effect of intensity-controlle d aerobic endurance training was studied in adult female and male rats that ran 2 h/day, 5 days/wk, in intervals of 8 min at 85-90% of (V) over dot O- 2max and 2 min at 50-60% of (V) over dot O-2max, with adjustment of exercis e level according to (V) over dot O-2max every week. After 7 wk, the increa se in (V) over dot O-2max plateaued at 60-70% above sedentary controls. Ven tricular weights and myocyte length were up 25-30% and 6-12%, respectively. Work economy, oxygen pulse, and heart rate were sufficiently changed to in dicate substantial cardiovascular adaptation. The model mimics important hu man responses to training and could be used in future studies on cellular, molecular, and integrative mechanisms of improved cardiovascular function.