To judge a person’s maximum trunk extension performance as either age-appropriate or deconditioned is challenging. The current study aimed at determining age and anthropometrically adjusted maximum voluntary contraction (MVC) of back extensors considering the number and recovery time between trials. Thirty-one younger (20–30 years) and 33 older (50–60 years) healthy males performed five repetitions of maximal isometric trunk extensions in an upright standing position with randomized recovery times ranging between one to five minutes at one minute intervals. Torque values were normalized according to the individual’s upper body mass resulting in upper body torque ratios (UBTR). To evaluate the impact of age, recovery time, and fatigue on UBTR we applied a linear mixed-effects model. Based on surface EMG data muscular fatigue could be excluded for both groups. For all MVC trials, UBTR levels differed significantly between age groups (range of mean values: younger: 2.26–2.28, older: 1.78–1.87, effect size: 1.00) but were independent from recovery time. However, the older males tended to exert higher UBTR values after shorter recovery periods. The study provides normative values of anthropometrically and age-group adjusted maximum back extensor forces. For the investigated groups, only two MVC trials with a recovery time of about one minute seem appropriate.
Eduard Kurz, Christoph Anders, Philipp Schenk, and Hans-Christoph Scholle are with the Clinic for Trauma, Hand and Reconstructive Surgery, Division of Motor Research, Pathophysiology and Biomechanics, Jena University Hospital, Jena, Germany. Mario Walther is with the Institute of Medical Statistics, Computer Sciences and Documentation, Jena University Hospital, Friedrich- Schiller- University Jena, Jena, Germany. Address author correspondence to Eduard Kurz at Eduard.Kurz@med.uni-jena.de.