Using 30-s Prone Back Extension Repetition Maximum Test to Predict Concentric and Eccentric 1 Repetition Maximum Squat Strength in Young and Older Adults.

Background: One repetition maximum (1RM) testing depends on lifting heavy loads which can put older adults at risk for injury and thus is nonfeasible. Thus, there is a great need for alternative 1RM testing methods, which are safe, patient-friendly, and clinically applicable, in older adults. Notably, aging-induced loss of muscle strength is greater for concentric than eccentric strength. However, there is a lack of information on unique 1RM for concentric and eccentric squat strength. Such information can lay the framework to design novel and effective resistive squat exercise programs in line with the principles of precision rehabilitation for various clinical populations. Purpose: To investigate if the 30-s prone back extension repetition maximum test can predict 1RM concentric and eccentric squat strength in young and older individuals. Methods: We enrolled and tested participants from 2 age groups: young: 21-35 years and older: 55-75 years in our cross-sectional study. Our main outcome measures were 30-s prone back extension repetition maximum and 1RM of concentric and eccentric back squat strength. All strength measures were normalized for body weight. Results: Thirty-second prone back extension repetition maximum significantly predicted 1RM concentric (p=0.030, ß = 0.56; 95% CI: 0.006-0.102) and 1RM eccentric squat strength (p=0.041; β = 0.030, 95% CI: 0.001-0.058) in young and older adults, respectively. In addition, we obtained a trend toward significance for the relationship between 30-s prone back extension repetition maximum and 1RM eccentric (p=0.078) and 1RM concentric (p=0.066) squat strength in young and older adults, respectively. Discussion: Novel data from our study show that 30-s prone back extension repetition maximum can predict 1RM of concentric and eccentric squat strength in young and older adults, respectively. Thus, clinicians and rehabilitation professionals can use our novel equations to design concentric- and eccentric-biased resistive training programs in young and older adults, respectively, without testing for 1RM.