gms | German Medical Science

Objective: Mean power in concentric phase of lifting is considered as a better indicator of fatigue druing weight exercise set performed with maximal effort than peak power. Though, this has been proved for ordinary exercise (bench press) with stable support [1], there are no data specifying the most sensitive parameter of fatigue during weight exercise performed on unstable support surface. The study compares the decline of peak and mean power during chest presses and squats performed on unstable surface to failure.

Material/Methods: A group of 14 physical education students (age 24.8±2.7 y, height 184.7±8.2 cm, weight 78.3±7.8 kg) performed randomly in different days barbell chest presses on Swiss ball and barbell squats on Bosu ball (both with 70% 1RM) to failure. However, only 16 reps of chest presses and 21 reps of squats were taken into consideration because majority of the subjects were able to perform this number of repetitions on particular surface. The system FiTRO Dyne Premium based on precise velocity sensor with sampling rate of 100 Hz was used to monitor basic biomechanical parameters involved in weight exercise. Peak and mean values of power in concentric phase of lifting were obtained. Fatigue index was calculated as a ratio of power decline (Ppeak-Pmin) and peak power (Ppeak).

Results: Mean power in entire concentric phase of lifting decreased more profoundly than peak power during both chest presses on Swiss ball (from 396.3±23.7 W to 234.1±16.7 W, and from 701.8±46.0 W to 492.0±28.7 W, respectively) and squats on Bosu ball (from 421.6±25.6 W to 280.6±18.1 W, and from 783.8±52.4 W to 588.3±32.7 W, respectively). This may be also documented by significantly (p<0.05) higher fatigue index calculated from mean than from peak power of chest presses (40.9% and 29.9%, respectively) and squats (33.4% and 24.9%, respectively). In both cases mean power in entire concentric phase of lifting started to gradually decrease after one-two initial repetitions, whereas peak power towards the end of such exhaustive sets. This finding is in agreement with our previous study [2] that showed greater decline of Pmean than Ppeak during both stability and instability chest pressess with more pronounced differences at 80% 1RM rather than at 60% 1RM. While in the present study the difference between fatigue index of Pmean and Ppeak during chest presses with weight of 70% 1RM was 11.0%, in the study of Jeleň [2] it was 9.1% at 60% 1RM and 14.4% at 80% 1RM. These findings indicate that peak power is less sensitive to fatigue at higher than at lower weights lifted. Moreover, our other experiments showed significantly greater inter-day variability in peak power throughout exhaustive repetitions compared with two-three initial values. In practice it would require multiple day-to-day trial protocols in order to obtain required reproducibility.

Conclusion: These findings indicate that mean power in entire concentric phase of lifting is more sensitive indicator of fatigue induced by instability resistance exercises than peak power.