Isokinetic versus isotonic variable-resistance training.

A study of isokinetic exercise and isotonic variableresistance training divided 12 individuals into four groups: 1) control; 2) isotonic variable-resistance training; 3) low-speed isokinetic (5, 10, and 15 rpm); and 4) high-speed isokinetic training (30, 40, and 50 rpm). All exercised groups showed good gains in strength when tested isometrically, isotonically, and isokinetically. However, when the individuals were tested for motor performance, the high-speed isokinetic group dominated (5.38% gain in the vertical jump versus 3.87% for the slow isokinetic, and 1.57% for the isotonic variable resistance; 9.14% gain in the standing broadjump versus 0.42% and 0.28%; and 10.11% gain in the 40-yard dash versus 1.12% and 1.35%). Training should be specific in all training and rehabilitation programs, with the athlete/patient training in the manner most similar to his athletic event or performance. The spectrum of strength is varied and is a major component of any sport participation. A method of strength training for each athletic event ideally would be the optimum way of improving that athletic performance. The major modes of strength training are isometric, isotonic, and isokinetic exercise. It is important to understand the difference in each of these forms of exercise. Isometric contraction occurs when resistance of sufficient magnitude prevents motion. This allows maximum loading, but only in one point in the range of joint motion. Past reports have shown little effect on motor performance tests. I Isotonic contraction results from exercise done through a range of joint motion with a set resistance. Because of the physiologic skeletal lever, neither the force on the system nor the resistance is constant during the range of motion. Therefore, loading occurs at the weakest point in the system, while the rest of the system is working at less than capacity. This is not efficient. The variable-resistance concept (of which Nautilus equipment (Nautilus Sports/Medical Industries, DeLand, FL) is an example) eliminates some of these disdavantages by using a cam effect. Others use friction, hydraulics, or levers and pulleys. Peterson,2 in 1975, tested individuals at the US Military Academy and reported results as high as 58% improvement on a leg press. These individuals were tested on the same devices on which they trained. Pipes and Wilmore’ did a study on variable-resistance exercise procedures which showed an increase in muscular strength, but values were not as high as in the Peterson2 2 study (27% in the leg press versus 58%). Isokinetic exercise is not doing an isotonic exercise at a fast speed. Isokinetic exercise is entirely different from the other modes. It controls the speed of exercise (a fixed speed) and varies the resistance. This variable-resistance exercise totally accommodates fatigue and pain. It maximally loads the muscle at every point in the range of motion. The increased strength associated with isokinetic exercise has been attributed to the fact that an accommodating contraction enables one to do more work in the same period of time than is possible in either constant resistance or variable resistance. The studies by Pipes and Wilmore’ have shown the superiority of isokinetics over isotonic exercise when functional tests are compared. To date, no study has compared isokinetic (accomodating resistance) with the variable-resistance modes (e.g., Nautilus). This study was designed to investigate the ability of these modes to effect changes in the muscular strength of the quadriceps (knee extensors) and hamstrings (knee flexor) muscles in adolescent males. Both isokinetic slow and fast speeds were examined. MATERIALS AND METHODS Twelve adolescent males between the ages of 16 and 18 voluntarily participated in a six-week training program. They were randomly assigned to four categories: control, variable resistance (Nautilus), isokinetic low speed, and isokinetic high speed. This study was performed in the spring, when none of the individuals was participating in or in training for any specific athletic team or performance. Eight had played high school football the previous fall. Four classified themselves as nonathletes and only participated in recreational sports. ’ Presented at the Sixth Annual Meetmg of the Amencan Orthopaedic Society for Sports Medicine, Big Sky, MT, June 30 to July 3, 1980 tAddress correspondence to Michael J Smith, MD, 615 Eleventh Street North, St Petersburg, FL 33705 by guest on August 2, 2009 ajs.sagepub.com Downloaded from