Determinants of maximal inspiratory force and handgrip in a population of healthy elderly subjects

Peripheral muscle strength decreases with aging, affecting up to 50% of >80 years old subjects. The relationship between muscle depletion and a reduced respiratory strength has not been extensively studied. From a cohort of healthy old subjects (the Proof cohort), we compared the determinants of a reduced maximal inspiratory pressure (MIP) and those of a reduced handgrip (HG) as an index of whole body muscle force. We measured MIP, and HG of the dominant arm, in 393 healthy subjects aged 72±1 years old. Body composition (biphotonic absorptiometry) and daily energy expenditure (24h_DEE) questionnaire were determined 3 years before. Fat free mass (FFM) was calculated for whole body and for the trunk and was indexed to height (FFMI). Mean MIP was 77±26 % of predicted value and 90 subjects had a MIP value below normal. Mean HG was 106±19% of predicted value and was reduced below normal in 30 subjects. We found only a weak correlation between MIP%pred and HG%pred (r=0.175, P FFMI, the percentage of FFM of the trunk, and 24h_DEE were the only significant covariates which influenced the reduction of MIP. HG reduction was determined by sex, body FFM and 24hDEE. We conclude that the determinants of a reduction of MIP in elderly differed from those of the HG force, suggesting a differential regulation of respiratory muscle force.