Peripheral isokinetic muscle function and cardiorespiratory capacity in coronary artery disease patients

Objective: The aim of this study was to determine if the diminished aerobic capacity of coronary artery disease (CAD) in male patients is accompanied by a peripheral impaired skeletal muscle function and to assess the correlation between the isokinetic strength and aerobic aptitude of these patients.

Materials and methods: Fifteen CAD patients and 15 healthy subjects(age: 60 ± 6 vs 57 ± 3.5 years old) performed both maximal exercise testing, an isokinetic assessment of knee muscles and a 6-minute walking test. The quadriceps and hamstrings were tested at 150 and 180°/s while being monitored with ECG. The cardio-respiratory and mechanical parameters (VO2, VT, HR, and power) were measured at ventilatory threshold and at maximal effort during a maximal exercise testing.

Results: Isokinetic assessment was conducted successfully with all patients. No rhythm irregularity or hemodynamic anomalies were observed in the 2 groups. Muscle testing revealed significant strength impairment. Quadriceps peak torque, at 150°/s was 77 ± 16 Nm in patients vs. 99 ± 23 Nm in controls, (p<0.01) while at 180°/s the values were 71 ± 14 vs. 91 ± 23 Nm, (p<0.01), respectively. For the hamstrings the values were respectively 49 ± 16 vs. 66 ± 14 Nm, (p <0.01) and 47± 10 vs. 60 ± 12 Nm, (p<0.01).

CAD subjects presented a deficient aerobic capacity compared to the healthy control group at maximal effort (Vo2 maximal uptake: Vo2 max: 20.34± 4.95 vs. 29.16 ± 7.68 ml mn $^{-1}$ kg $^{-1}$ , (p=0.01); maximal ventilation Ve max: 58.18 ± 16.28 vs 84 ± 24.45 ml mn ${-1}$ , (p<0.05); heart rate: HR max: 118 ± 21 vs 152 ± 13 beats mn $^{-1}$ , (p<0.001); maximal power: P max: 102 ± 31 vs. 153 ± 33 W. (p<0.001) and at ventilatory threshold: VT (Vo2: 13.77 ± 2.33 vs. 17.08 ± 3.59 ml mn $^{-1}$ kg $^{-1}$ , (p< 0.05); VE: 29.64± 6.64 vs. 37.76 ± 7.2 ml mn $^{-1}$ ,(p<0.05); HR: 86 ± 14 vs. 111 ± 15 beats mn $^{-1}$ , (p=0.001); but no significant difference was noticed for power (P: 61 ± 12 vs. 76 ± 24 W:). We also noticed that isokinetic muscle strength and O2 peak were not related to each other and are therefore independent.

Conclusion: This study shows that CAD patients, compared to healthy subjects, have impaired cardio respiratory capacities which are accompanied by increased muscle fatigability. Isokinetic muscle strength and maximal aerobic capacity are independent of each other. An isokinetic muscle assessment in these patients must be conducted systematically and seems to have a considerable value in cardiovascular rehabilitation.