The Effect of High-speed Power Training on Muscle Performance, Function and Pain in Older Adults With Knee OA

The study compared 12 weeks of explosive high-speed power training with traditional slow-speed strength training. Outcome measures included muscle performance: leg press (LP) and knee extension (KE) one-repetition maximum (1RM) and LP peak power (PP), velocity at peak power (PPV) and force at peak power (PPF) from 40%-90% of the 1RM. Measures of function consisted of the 400-meter walk (400-m W), Berg Balance Scale (BBS), timed chair rise (TCR) and self-reported function and pain using the WOMAC.

Participants reported to the laboratory for 2 weeks of baseline measurements. On visit 1, subjects were explained the study and completed an informed consent document. On visit 2 and 3, muscle performance and functional measures were obtained. The following week, all muscle performance and functional measures were repeated to establish reliability. At the end of baseline testing, participants were randomized to treatment. Following the 12-week RT intervention, post-training muscle performance and functional measures were obtained.

Resistance Training Protocol. Volunteers randomized into high-speed power training (HSPT) and slow-speed strength training (SSST) exercised 3 times per week for 12 weeks using computer-interfaced Keiser a420 pneumatic leg press and knee extension RT equipment (Fresno, CA). For HSPT, each training session consisted of 3 sets of 12-14 repetitions at 40%1RM. Participants performed an explosive movement at high speed during the concentric phase of each repetition, paused for one-second, and performed the eccentric portion of the contraction over 2 seconds. Volunteers randomized into SSST also exercised 3 times per week for 12 weeks with each training session consisting of 3 sets of 8-10 repetitions at 80%1RM. The participants performed each movement at a slow velocity (2 s for concentric phase of the repetition), paused for one second, and performed the eccentric portion of the contraction over 2 seconds. CON met three times a week for warm-up and stretching exercises, but performed no RT. HSPT and SSST participated in the same warm-up and stretching exercises as CON.

Measures Maximal strength and power. Leg press and seated knee extension 1RM were obtained using Keiser pneumatic RT equipment fitted with a420 electronics. The seat of both the recumbent LP and KE apparatus was positioned to place the hip and knee joints between 90 and 100 degrees of flexion. The 1RM was obtained by progressively increasing resistance until the subject was no longer able to push out one repetition successfully. The Borg Scale was used to assist in evaluating when 1RM (combined with perceived maximal effort) was reached. Peak muscle power was obtained at 40%, 50%, 60%, 70%, 80% and 90% of the 1RM approximately 30 minutes after 1RM testing (8,9). Participants were instructed to exert "as fast as possible" at each relative percentage of the 1RM. Three attempts were made at each resistance and the greatest PP output obtained at each resistance was used in the analysis. The corresponding PPV and PPF were obtained for each external resistance from 40%-90% 1RM. The 1RM was measured bi-weekly in HSPT and SSST only and relative training intensity was adjusted accordingly to ensure adequate overload during training. Post-training muscle performance measures were obtained using loads relative to the initial baseline 1RM as well as the post-training 1RM.

400 meter self-paced walk (400-m W). Participants were instructed to walk at a pace they could maintain without overexerting themselves until they complete the 400-m W or could no longer continue. Standardized verbal encouragement was given at 30-second intervals during the walk. Participants taking longer than 15 minutes to complete the 400-m W were considered unable to successfully perform the test.