In half a million UK adults, each 5 kg of lower grip went with 16–20% higher mortality

Prospective cohort of 502,293 adults aged 40–69 (54% women). Mean follow-up 7.1 years; 13,322 deaths.

Women and men respectively: cardiovascular mortality 1.19 (1.13–1.25) and 1.22 (1.18–1.26); respiratory mortality 1.31 (1.22–1.40) and 1.24 (1.20–1.28); all cancer 1.17 (1.13–1.21) and 1.10 (1.07–1.13).

The study defined weakness as grip under 26 kg in men and under 16 kg in women. Adding grip to an office-based risk score raised the C index by 0.013 for all-cause and 0.012 for cardiovascular mortality, a small improvement in prediction.

The authors say reverse causation and residual confounding cannot be excluded. UK Biobank volunteers are healthier than the general population.

This is why grip is in the battery. The small gain in the C index is also why the app does not turn your grip into a risk score: it adds a little to prediction for a population, and says much less about one person.