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Ruth Spitsbergen Kines 326 Isokinetic Dynamometry and Resistance Assessment Abstract Background: Muscle strength is the greatest amount of force produced by a given muscle group. Muscle endurance is the ability for a muscle group to sustain that force over a longer period of time. AIM: The purpose of this study was to introduce the isokinetic dynamometry machine to students to evaluate muscle force (torque in ft-lbs) and exertion at the knee for angles of extension and angles of flexion at various degrees. The assessment also compared maximum strength fatigue with endurance fatigue. Method: 5 subjects, three females and two males, (mean age±22 SD ±.63) warm-up on a stationary cycling ergometer for approximately five minutes. Subjects’ questionnaire consisted of height (inches), weight (lbs), and age (years). This information was imputed into the Biodex software program where individual data would be generated. Trial one had three subjects one male and two females participate in 5 sets of maximal force exertion of the dominant leg at contraction and relaxation rates ranging from 30- 300 degrees/second. Trial 2 consisted of one male and one female with the same questionnaire and warm up. This test consisted of flexing and extending the quadriceps for 80b repetitions at an angle of 180 degrees/sec. This test is to maintain force throughout the entire 80 repetitions as consistently as possible. The strength test measured peak torque for extension and flexion at 30 degrees. Results: During trial 1, subjects exerted an average of 177.6 ftlbs±67.29 at 30 degrees/sec and 51.66ft-lbs±24.22 at 360 degrees/sec. During trial 2, subjects averaged a fatigue of work output of 77.2%±4.10 over 80 repetitions. As velocity increased force output of the knee extension and knee flexion decreased. Conclusion: At an increased rate of contraction, force output contraction decreased. For the endurance test as repetitions increased the force output decreased. Questions: Table 1: Individual and Mean Values for Peak Torque at 30 deg/sec Extension (ft-lbs) Flexion (ftlbs) Rachel 106.1 Sam 219.8 Chris 213.0 Total 538.9 Mean(±SD) 179.63(±63.77) 65.8 98.2 108.6 272.6 90.87(±)22.32 2. The results indicate that they have greater extension torque than flexion torque because all subjects have greater torque capabilities in their extensors opposed to flexors. The weaker the hamstrings are compared to the quadriceps, the more susceptible an ACL injury is to occur. 3. Table 2 Isokinetic Knee Extension vs. Contraction Velocity 250 Extension Torque (ft-lbs) 200 Isokinetic knee Extension vs. Contraction Velocity 150 Subject 1 Subject 2 100 Subject 3 50 0 0 100 200 300 Contraction Velocity (degrees/second) 400 As the contraction velocity increases on the graph you see a decrease of torque produced over degrees/time (speed). 4. Warming up will increase the length of muscles but excessive stretching and shortening will impair the ability to produce optimal force during contractions. Not warming at all can exert the muscles too quickly without allowing enough blood supply, actin and myosin interaction and ATP binding to occur therefore creating a potential injury to the muscles. 5. Table 3 Total Work 180 degrees/sec David Jamie Total work 4160.9 3677.2 Work 1st and 3rd Work last 3rd % Fatigue 2701.4 1991.9 Mean±SD 3919.05± 342.02 2346.6±501.69 536.7 80.1 720.3 74.3 658.5±87.39 77.2±4.01 Data showed a significant decrease in torque as repetitions prolonged to eighty. Fatigue is responsible for a decrease in force and power output during prolonged exercise and the metabolic role reasoning for the depletion of energy substrates such as ATP and other fuel sources which assist the production of ATP (Hargreaves, 2005) ATP production is essential to maintain force and power production during exercise therefore depletion and other biproducts can be the reason for fatigue. (Hargreaves, 2005) Also in exercises that are a new stimulus to the subjects that are not conditioned for this specific test are more likely to fatigue faster than a trained individual. 6. Muscle meets are force demands by recruiting other muscles groups and by metabolic fuel sources. As an action continues and force demands are increasing, type ll a (fast twitch) and llb (fast twitch) will be stimulated and excited. (Astorino, 2012) For Trail one muscle force was at its peak for contraction at the slowest velocity first set of 5 reps. As the speed of contraction and velocity sped up more fibers were recruited and excited thus fast twitch lla and llb were firing. Trial 2 showed a lot more of type 1 fibers working but also type ll working with type one to maintain contractions for prolonged amount of reps. Over time type ll will fatigue and produce more byproduct due to lack of enough fuel supply and rest therefore slowing down contraction and force output. Type 1 will continue to fire, generating less force but will endure till the end of the trial.