Background and Aims:

Diminished muscle strength and perceived fatigue are frequently associated with exercise intolerance in patients with coronary heart disease (CHD) and may be responsible for the diminution of their daily physical activities and quality of life. However, skeletal muscle fatigue and its mechanisms remain poorly documented in CHD patients. The aim of this study was to compare the effects of combined aerobic and resistance training versus aerobic training on skeletal muscle fatigue assessed with electromyography in CHD patients.

Methods and Materials:

Sixteen men with documented CHD (54 +/- 8 years) underwent an assessment of quadriceps skeletal muscle fatigue on an isokinetic apparatus with surface electromyography (SEMG) measurements. Patients with CHD were then randomly divided in a combined aerobic-resistance (CAR, n = 8) or an aerobic training group (AT, n = 8). Patients trained 1 hour, 3 times per week during 7 weeks. The maximal voluntary isometric force (MVIF) of the quadriceps was quantified as a measure of muscle strength and isometric endurance (IE) was defined as the time required to sustain a contraction at 50% of MVIF until exhaustion. SEMG signals were recorded from vastus lateralis (VL), rectus femoris (RF) and vastus medialis (VM) during isometric endurance. The root mean square (RMS) and the median frequency (MF) were directly calculated on a computer and then normalized (in % of initial value).

Results:

The quadriceps MVIF increased significantly in the CAR training group (229 +/- 52 vs. 278 +/- 45 N.m^-1, P < .05) but did not change for the AT group (229 +/- 52 vs. 214 +/- 48 N.m^-1, ns). The IE time did not change after training in both group (pre: 64 +/- 17 sec., CAR: 66 +/- 12 sec. and AT: 60 +/- 3 sec.). After training, the RMS values did not differ in both training group for the VL and VM, but RMS value was lower for the RF in the CAR group (P < .01). Compared with pre training data, the MF values were significantly higher for the VL and VM (P < .0001) in the AT group and also higher for the VL, RF and VM (P < .0001) for the CAR group. Compared with AT group data, the MF values in the CAR group were higher for RF (P < .0001) and VM (P < .01).

Conclusions:

The CAR training is more effective than AT in the diminution of skeletal muscle fatigue in CHD patients. The CAR training improves quadriceps strength, endurance, motor unit functioning (RMS) and SEMG fatigue indexes (MF) during exhaustive isometric contraction. A lower level of motor units recruitment and less muscle metabolites accumulation could be responsible for those SEMG modifications. The use of SEMG in the skeletal muscle fatigue assessment may be particularly useful for the evaluation of training interventions efficacy in CHD patients.

Section Description

For more information, contact Marilyn Thomas (204) 488-5854