Force-velocity characteristics of the knee extensors: an indication of the risk for physical frailty in elderly women.

OBJECTIVES

To examine the relationship between muscle strength, speed of movement, muscle mass (MM), and functional performance in elderly women and to determine optimal threshold values below which physical frailty occurs.

DESIGN

Survey.

SETTING

University-based laboratory.

PARTICIPANTS

Institutionalized women (N=123; mean age, 79.67 ± 5.2y).

INTERVENTIONS: Not applicable.

MAIN OUTCOME MEASURES: Force-velocity characteristics of the knee extensors were evaluated by using isometric, isokinetic, and ballistic tests on a motor-driven dynamometer. Isometric (ISOM) strength, dynamic strength, maximal speed of movement (SoM, unloaded), and speed of movement with standardized resistance of 20% (S(20)), 40% (S(40)), and 60% (S(60)) of the isometric maximum were recorded. MM of the upper leg was determined by using computed tomography. The modified Physical Performance Test (mPPT) was used to assess functional performance.

RESULTS

Force-velocity characteristics (r varied from .31-.68) and MM (r=.41) correlated significantly with functional performance (P<.05). In a forward stepwise regression model, only SoM and ISOM strength remained independently associated with mPPT score (R(2)=.49), with SoM accounting for most of the variance. The threshold value that optimally differentiates between women with mild (mPPT score, 25-31) or without (mPPT score ≥32) physical frailty was 350°/s for SoM and 1.46N m/kg for ISOM strength. Sensitivity and specificity ranged from 74% to 77% and 71% to 77%, respectively.

CONCLUSIONS

SoM is a key component in the onset of functional difficulties in elderly women. Exercise interventions specifically targeting muscle power (by including exercises at high velocities) thus might be crucial to prevent functional decline.