Using Isometric Squat Strength to Predict Concentric and Eccentric Squat Strength in Young and Older Adults

Resistive squat exercise is a well-established technique to enhance the strength of muscles and bones of the back extensors in humans. Rehabilitation programs aimed at strengthening the muscles and bone of the back require the knowledge of the patient's 1 repetition maximum (RM) of squat exercise. Finding the 1RM value of squat exercise could lead to injury or seem nonfeasible because of the higher weights involved, especially in older adults.

To investigate the predictive relationship between the maximum voluntary isometric squat strength and the 1RM concentric and eccentric squat strength in young and older individuals.

In our cross-sectional study, individuals from two age populations, 21-35 years (young) and 55-75 years (older) were recruited and participated in two visits within a two-week period. Our main outcome measures were: Maximum voluntary isometric squat strength (IsoMax) and 1RM of concentric (ConMax) and eccentric (EccMax) back squat strength were calculated for young and older adults. All the strength measures were normalized for body weight.

IsoMax was a significant predictor of the ConMax (p = 0.003; Normalized ConMax = 0.708 + 1.376(Normalized IsoMax); 95%CI: 0.583-2.169) and EccMax (p = 0.003, Normalized EccMax = 0.844 + 1.433(Normalized IsoMax); 95%CI = 0.582-2.284) in older adults only. There was a trend toward significance for the relationship between IsoMax and ConMax (p = 0.058) in young adults.

Our novel findings show that safe techniques for muscle strength assessment, such as maximum voluntary isometric squat strength, can be utilized in older populations to predict their 1RM of concentric and eccentric squat strength. Our novel equations provide the information necessary for designing effective rehabilitation regimes for strengthening the muscles and bone of the back in older adults.