Validity and reliability of the T-Force and Chronojump systems to measure movement velocity on resistance machines with older adults.

The current study aimed to analyze the validity and reliability of the T-Force and Chronojump systems to measure the movement velocity in the leg press (LP) and chest press (CP) exercises in older people. Eighteen older adults (6 men and 12 women, 79.9 ± 8.5 years) performed a set of procedures over three weeks: (i) the first week was to familiarize participants with the testing procedures, (ii) the second was to perform a progressive loading test until reaching one-repetition maximum (1RM) in the LP and CP, and (iii) in the third week, participants performed three repetitions against five loads (40, 50, 60, 70, and 80% of 1RM). The mean velocity of each repetition was recorded simultaneously through the T-Force and Chronojump devices. Linear regressions (coefficient of determination [r] and standard error of the estimate [SEE]) analyzed the inter-device validity, and Bland-Altman plots illustrated the systematic differences between devices. A mixed-effects model estimated the mean velocity differences between devices. The relative reliability was analyzed by the intra-class correlation coefficient (ICC[1,k]), while the absolute reliability was by the standard error of measurement (SEM) and the coefficient of variation (CV). The results showed that the T-Force and Chronojump presented a high association level in measuring mean velocity in the LP and CP (r range: 0.96-0.99; SEE range: 0.01-0.02 m·s) and low systematic bias (0.02-0.03 m·s). The mean velocity values of T-Force were significantly higher than Chronojump only for 40% 1RM (p = 0.04). Excellent reliability inter-device (ICC range: 0.95-0.98; CV range: 1.7-3.2%) and intra-device (ICC range: 0.90-0.97; CV range: 3.4-6.5%) was observed. This study shows that the T-Force and Chronojump systems are valid and reliable for measuring movement velocity in the CP and LP machines when used by older adults.