Isokinetic versus one-repetition maximum strength assessment in chronic heart failure

Reduction in exercise capacity in patients with chronic heart failure (CHF) has been partially attributed to decreased muscle strength. Training studies reported important variations in strength increases during rehabilitation, ranging between 5% and 70% and depending on the measurement technique: isokinetic dynamometry or the one-repetition maximum (1RM) methods. Therefore, the question arises if both techniques assess the changes in muscle strength in a comparable way.

Thirty patients with CHF, New York Heart Association class II-III, with mean baseline VO2peak of 14.8 +/-3.0 mL x kg(-1) x min(-1) and mean baseline left ventricular ejection fraction of 23.5% T 5.5%, were assessed for knee extensor and knee flexor strength before and after 40 training sessions by isokinetic dynamometry and 1RM method. These two strength measurement techniques were compared using the Bland and Altman method for agreement.

Knee extensor muscle strength increased by 7.4% and knee flexor strength increased by 18.7% if measured by isokinetic testing. With the 1RM method, knee extensor and flexor strength increased by 36% and 100%, respectively. Both techniques were not in agreement for muscle strength assessment; improvements were more important with the 1RM method. Furthermore, statistical analysis showed that the 1RM technique was overestimating strength increases in comparison with isokinetic evaluation, especially for higher strength levels.

In the follow-up of exercise training programs in patients with CHF, isokinetic measurements should be preferentially used to limit bias between measurements at different times.