Five-year changes in cardiorespiratory fitness are related to fat-free mass and body weight in men but not women.

Background
Handgrip strength (HGS) and cardiorespiratory fitness (CRF), which is defined by maximal oxygen uptake (VO2peak), are important parameters of physical fitness. Low HGS and CRF are associated with a greater risk of cardiovascular diseases and higher all-cause mortality in cross sectional settings. A means to prevent a reduction in HGS and CRF is physical exercise which has a plethora of health benefits. Among these is a presumed positive effect on anthropometric parameters like body mass index (BMI), body weight, fat mass (FM), fat-free mass (FFM), waist and hip circumference. Previous studies have primarily focussed on cross-sectional settings. Hence, we evaluated the association of changes in HGS and CRF in a longitudinal-population-based study. Specifically, we related annualized changes in HGS (Δ HGS) and CRF (Δ CRF) with changes in anthropometric risk factors in men and women.

Methods
Data from the population-based Study of Health in Pomerania (SHIP) of a baseline study (SHIP-Trend-0) and the follow-up study (SHIP-Trend-1) with 1,232 study participants (639 women; 51,9%) were used. CRF was assessed with a standardized cardiopulmonary exercise test (CPET). Handgrip strength was measured with a hand dynamometer. Linear regression models were used to evaluate the relationship between Δ HGS/CRF and the changes in anthropometric data. These were adjusted for age, baseline outcome, smoking baseline and follow-up. FFM was also adjusted for FM and vice versa. Additional analyses included the presence of metabolic syndrome and physical activity, the exchange of outcome and exposure, median as reference value and stratification by menopause at baseline. A trajectory analysis was also carried out by stratification of study participants into three groups based on absolute change of exposure.

Results
From baseline to follow-up absolute VO2peak increased by 53 ml/min in women and decreased by 36 ml/min in men. In addition, HGS decreased by 3.5 kg in men and by 0.8 kg in women. BMI, body weight, waist circumference and FM increased during the same study period, while FFM decreased in both sexes. A decrease in VO2peak was significantly associated with an decrease in FFM in men (β= 0.867 kg; 95%-confidence interval [CI]= 0.004;1.73; p=0.049). A decrease in VO2peak was significantly associated with a decrease of body weight in men (β= 1.148 kg; 95%-CI= 0.039;2.25; p=0.042). There was no significant relationship between the Δ VO2peak and the other anthropometric data in men. In women, no significant relations were found between the Δ VO2peak and in Δ anthropometric data. In both sexes, no significant association could be found for Δ HGS and Δ anthropometric data.

Discussion
In our study, we were able to show that changes in HGS are not related to changes in anthropometric parameters. In men, we found that a change in CRF was related to changes in anthropometric parameters, whereas we found no correlation in women. This suggests that the benefits of a high CRF are potentially sex-specific. Previous studies showed that body shape and composition as well as sex influence tissue-specific oxygen demand. However, by including menopause, we were able to relativize the influence of oestrogens in women. In earlier cross-sectional studies, HGS and CRF were cited as good parameters for the clinical assessment of cardiovascular risk factors. In longitudinal studies similar to our results, these results are not clear, and deserve further research.