Isokinetic strength ratios: Conventional methods, current limits and perspectives

Abstract

Muscular performance and the risk of injury may depend on the balance of opposing muscle groups (Tam et al., 2017). It is a common and useful practice in clinical set up to assess the relative balance of opposing muscle groups around a joint by comparing strength ratios of agonist and antagonist muscle groups (Sapeda, 1990). This ratio is classically explored using an isokinetic dynamometer (Dvir, 2004). Isokinetic technology has become a popular method in order to assess muscle function in both clinical and research settings (Drouin et al., 2004). The concept is based on the measure of muscle torque recorded during isolated joint exercise within which angular velocity remains constant. Isokinetic dynamometers provide an accommodating resistance equal and opposite to the muscular forces applied for maximum external-force output with changing positions of the joint (Sapeda, 1990). The agonist-antagonist muscle balance is explored through different isokinetic ratios. First, the conventional ratio represents a concentric antagonist/agonist ratio (Evangelidis et al., 2015). The second ratio used is called the functional ratio (eccentric antagonist/concentric agonist) and it has been developed especially for the evaluation of athletes (Mont et al., 1994; Scoville et al., 1997). Other authors have proposed a mixed functional ratio, combining two different angular velocities (Croisier et al., 2002; Forthomme et al., 2013; Evangelidis et al., 2015). However, in clinical practice, the isokinetic ratios are calculated systematically with respective simple peak torque (PT) measurements for agonist and antagonist muscle groups. Some sectorial methods have emerged and appear to be conceptually very promising, but are little exploited and remain exclusive to the field of research. The development of these methods would be of interest to appreciate the muscle balance in the field of rehabilitation and sport. The objective of this opinion article letter is to provide critical point of view about the classical method associated with PT, and to present the emerging methods.