Handgrip strength measurement protocols for all-cause and cause-specific mortality outcomes in more than 3 million participants: A systematic review and meta-regression analysis

Background & aims: Handgrip strength is a strong predictor of the risk of mortality. The objective of this systematic review was to analyse handgrip strength measurement protocols used in all-cause and cause-specific mortality studies. Method: A systematic search of PubMed/MEDLINE, Web of Science and Scopus was conducted from inception to February 2022. Prospective cohort studies with objective measures of handgrip strength were included. Studies had to report at least one all-cause, cancer, or cardiovascular mortality outcome. The quality of the included studies was assessed using the Newcastle Ottawa Scale. Meta-regression was used to quantify the bias associated with handgrip strength values in relation to the use of different measurement protocols. Results: Forty-eight studies with a total of 3,135,473 participants (49.6% women) were included. Half of the studies controlled body position, 39.6% arm position, 33.3% elbow position, 12.5% wrist position, 13% handgrip duration, 23% hand-adjustment to dynamometer and 12.5% verbal encouragement. The number of measurements, the laterality of the hand tested, and the estimation method of the handgrip strength value varied considerably between the study protocols. The spline regression model showed a non-linear inverse association between the values of handgrip strength and the number of protocol items controlled. Handgrip strength was higher when the number of measurements per hand or arm position was not controlled. Conversely, handgrip strength was lower when elbow position was not controlled or verbal encouragement were not provided. Conclusion: In general, the protocols used to assess handgrip strength in mortality studies are incomplete and highly heterogeneous. Handgrip strength values were higher when studies controlled fewer handgrip strength measurement protocol variables. There is a need to improve the controlling of handgrip strength measurement protocols and to standardise the method to enhance the accuracy of mortality risk estimates associated with handgrip strength. PROSPERO registration number: CRD42022334929.