Aims To investigate the association between cardiorespiratory fitness (CRF) and muscle strength in late adolescence and the long-term risk of heart failure (HF). Methods A cohort was created of Swedish men enrolled in compulsory military service between 1968 and 2005 with measurements for CRF and muscle strength ( n = 1,226,623; mean age 18.3 years). They were followed until 31 December 2014 for HF hospitalization as recorded in the Swedish national inpatient registry. Results During the follow-up period (median (interquartile range) 28.4 (22.0-37.0) years), 7656 cases of first HF hospitalization were observed (mean ± SD age at diagnosis 50.1 ± 7.9 years). CRF and muscle strength were estimated by maximum capacity cycle ergometer testing and strength exercises (knee extension, elbow flexion and hand grip). Inverse dose-response relationships were found between CRF and muscle strength with HF as a primary or contributory diagnosis with an adjusted hazards ratio (95% confidence interval) of 1.60 (1.44-1.77) for low CRF and 1.45 (1.32-1.58) for low muscle strength categories. The associations of incident HF with CRF and muscle strength persisted, regardless of adjustments for the other potential confounders. The highest risk was observed for HF associated with coronary heart disease, diabetes or hypertension. Conclusions In this longitudinal study of young men, we found inverse and mutually independent associations between CRF and muscle strength with risk of hospitalization for HF. If causal, these results may emphasize the importance of the promotion of CRF and muscle strength in younger populations.

Living in a low socioeconomic status (SES) area is associated with an increased risk of cardiovascular events and all-cause mortality. Previous studies have suggested a socioeconomic gradient in daily physical activity (PA), but have mainly relied on self-reported data, and individual rather than residential area SES. This study aimed to investigate the relationships between residential area SES, PA pattern, compliance with PA-recommendations and fitness in a Swedish middle-aged population, using objective measurements. We included 948 individuals from the SCAPIS pilot study (Gothenburg, Sweden, 2012, stratified for SES, 49% women, median age: 58 years), in three low and three high SES districts. Accelerometer data were summarized into intensity-specific categories: sedentary (SED), low (LIPA), and medium-to-vigorous PA (MVPA). Fitness was estimated by submaximal ergometer testing. Participants of low SES areas had a more adverse cardiovascular disease risk factor profile (smoking: 20% vs. 6%; diabetes: 9% vs. 3%; hypertension: 38% vs. 25%; obesity: 31% vs. 13%), and less frequently reached 150 min of MVPA per week (67% vs. 77%, odds ratio [OR] = 0.61; 95% confidence interval [95% CI] = 0.46–0.82), from 10-minute bouts (19% vs. 31%, OR = 0.53, 95% CI = 0.39–0.72). Individuals in low SES areas showed lower PA levels (mean cpm: 320 vs. 348) and daily average MVPA (29.9 vs. 35.5 min), and 12% lower fitness (25.1 vs. 28.5 mL × min− 1 × kg− 1) than did those in high SES areas. Reduced PA and fitness levels may contribute to social inequalities in health, and should be a target for improved public health in low SES areas.

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