ISO-INERTIAL MEASUREMENT OF MUSCULAR STRENGTH:AN ASSESSMENT ALTERNATIVE

Abstract

Success in many sporting activities is dependant on strength and power. Sport scientists, coaches and athletes need reliable and valid tests to monitor changes in strength and power in order to maximise performance. Isokinetic testing remains one of the more popular methods of strength assessment, both for the clinician and researcher. Traditional isokinetic strength measures include peak and mean torque, while modem computerised analysis has allowed determination of parameters such as angular specific torque, torque acceleration energy, power and work. Isokinetic dynamometry may not be an appropriate method of assessment when one considers that the assessment typically occurs in non-weight bearing, open-kinetic-chain positions, as opposed to the more functional closed-kinetic-chain position common to most everyday activities. Isokinetic assessment is also normally confined to isolated muscle groups moving limbs through the cardinal planes of movement, and is not suitable for assessing the multijoint movements which are common to many sports. 'The fixed velocity of movement utilised during isokinetic testing is also not characteristic of most land-based sporting activities. Iso-inertial testing, on the other hand, more closely approximates functional movements which are characterised by accelerations of a constant mass. In many athletic activities the body is accelerated by biarticular muscles, and the design of appropriate iso-inertial apparatus will allow measurements to be made under these conditions. An apparatus has been designed in order to determine strength and power of the knee extensorthip extensor complex during a leg press movement in either a supine or seated position. The force and velocity data which is collected during testing is processed to determine peak force and power, and mean force and power during a leg press movement. Time to peak force and power, and rate of force development during various time intervals can also be determined from this data. This test has advantages over traditional iso-inertial leg strength tests, such as the vertical jump test, as the knee and hip angles are controlled at the commencement of the test, the test can be safely executed with maximal workloads, and detailed force power results are obtained at various workloads. This iso-inertial assessment tool is an improvement over isokinetic testing devices because the leg press testing procedure more closely replicates non-isokinetic, multi-joint activities such as running and jumping than does the typical, single joint, isokinetic testing procedure.