Optimal repetitions and contraction duration for reliable assessment of quadriceps maximal voluntary contraction and rate of force development in older adults with cardiovascular disease.

BACKGROUND

Quadriceps strength assessment is widely used in rehabilitation; however, testing protocols often rely on empirical approaches.

PURPOSE: To identify the optimal contraction time and number of attempts needed to reliably measure muscle strength (maximal voluntary contraction, MVC) and how quickly force is generated (rate of force development, RFD) in older adults with cardiovascular disease (CVD).

METHODS

We included 28 older outpatients undergoing cardiac rehabilitation (median age: 77 years). Quadriceps MVC and RFD at 0-50 ms (RFD50) and 0-100 ms (RFD100) were measured using isometric contractions. The tests examined how results varied based on 1) mean or maximum values, 2) dominant or both legs, and 3) the number of repetitions. Intra- (ICC1,1) and inter-rater correlation coefficients (ICC2,1) were evaluated across these patterns.

RESULTS

Mean to peak force was 1.73 seconds; only 2.4% required ≥3 seconds. A single trial with dominant leg yielded excellent reliability for MVC (ICC1,1 > 0.9; ICC2,1 > 0.9). For RFD50, moderate to good reliability was achieved with two repetitions of dominant leg or both sides (ICC1,1: 0.76-0.79; ICC2,1: 0.74-0.80), improving with three repetitions (ICC1,1: 0.75-0.86; ICC2,1: 0.79-0.84). For RFD100, two trials using dominant leg provided excellent reliability (ICC1,1: mean value 0.81, max value 0.89; ICC2,1: mean value 0.83, max value 0.85). Three repetitions provided consistently excellent reliability (ICC1,1: 0.88-0.93; ICC2,1: 0.86-0.92).

CONCLUSION

Reliable MVC can be assessed with a single 3-second trial in older adults with CVD. For RFD, two repetitions, especially using the dominant leg and maximal value, provide excellent reliability.