To examine before and after 6 wks of rehabilitation, the cardiorespiratory fitness, and resting cardiac parameter changes in soccer players having undergone anterior cruciate ligament reconstruction and to assess the benefits of a one leg cycling aerobic training program with the nonsurgical leg during the rehabilitation period. Twenty-four amateur soccer players took part in this study. The subjects were then randomly assigned to one of two groups--either an individualized one leg cycling aerobic program (training group) or without cardiorespiratory training (control group). The initial evaluation (T1) was carried out the first day of rehabilitation and the final evaluation (T2) within 42 days. Both consisted of resting cardiac echography measurement and maximal graded tests performed with the nonsurgical leg. For training group, peak power output, peak minute ventilation, the first (VT1), and second (VT2) ventilatory threshold values were significantly (P < 0.05) higher at T2 than at T1 (+13%, +10%, +7%, and +11%, respectively). For control group, peak power output, peak oxygen uptake, peak minute ventilation, and VT2 values decreased significantly at T2 in comparison with T1(-10%, -10%, -12%, and -11%, respectively). After hospitalization, significant reductions in end diastolic volume (T1, 116 +/- 17 ml; T2, 97 +/- 16 ml; P < 0.05) and stroke volume (T1, 75 +/- 14 ml; T2, 59 +/- 12 ml; P < 0.05) were also observed. For training group, the cardiac parameters were similar between T1 and T2. These results suggest that one leg cycling training during the rehabilitation seems to be an adapted method to stop the effects of hypoactivity.