Explosive Knee Extensor Muscle Function And Quality Is Associated With Walking Performance In Frail Older Individuals

Abstract

Age-related impairments in physical performance have been shown to be associated with knee extensor (KE) muscle function and quality, examined during the late isometric ‘steady state’ phase (MVC) of muscle contraction (≥300ms). However, the initial ‘explosive’ phase of contraction (rate of force development, RFD) may also play a key role in order to achieve adequate propulsion during walking. PURPOSE: To examine the association between explosive KE muscle function/quality and walking/stair ascending/chair rising in frail older individuals. METHODS: KE RFD 100ms after onset of contraction (RFD100) (KinCom), muscle thickness (Ultrasonography), 10m maximal walking speed (10m max), and 2-minutes maximal walking distance (2mwd) were evaluated in participants from the Healthy Ageing Network of Competences study (HANC) (n=65, 82.7±4.8 years, 66% women). Partial correlations were carried out between walking performance and quintiles of KE RFD100 function (Nm/s normalized to kg body mass; controlled for age, gender, height) as well as KE RFD100 quality (Nm/s normalized to cm muscle thickness; controlled for age, gender, height, muscle thickness). RESULTS: Quintiles of KE RFD100 function (lowest 0.77±0.33 vs highest 8.10±1.60 Nm/s/kg) correlated with 10m max (lowest 1.07±0.35 vs highest 1.36±0.23 m/s) (r=0.44, p<0.01) and 2mwd (lowest 102.6±30.3 vs highest 130.9±26.6 m) (r=0.43, p<0.01). Moreover, quintiles of KE RFD100 quality (lowest 23.0±9.5 vs highest 230.0±43.2 Nm/s/cm) correlated with 10m max (lowest 1.12±0.33 vs highest 1.37±0.24 m/s) (r=0.37, p<0.01) and 2mwd (lowest 108.2±28.0 vs highest 132.2±28.0 m) (r=0.38, p<0.01). CONCLUSIONS: In addition to other involved muscle groups and factors, explosive KE muscle function and quality is associated with walking performance in frail older individuals (explaining 19 and 14%, respectively). This supports the use of high-intense ‘explosive’ resistance training when doing interventions aimed at improving walking performance.