MUSCLES RESPOND DIFFERENTLY TO SIMILAR FORMS OF RESISTANCE EXERCISE
Hatzell, B., Johnson, S., Chaloupka, H., & Glass, S. C. (2008). Effects of velocity on muscle activation during leg extension exercise. ACSM 55th Annual Meeting Indianapolis, Presentation Number, 1624.
"Typically, resistance training programs are designed to maximize strength development. The velocity of lifting often varies as a function of intention or load. Understanding the optimal velocity for training with a standard resistance can help improve outcomes." This study examined the activation of the Rectus Femoris, Vastus Lateralis, Vastus Medialis, and Bicep Femoris muscles during a leg extension exercise at three different velocities. Males (N = 10) and females (N = 5) were tested on two separate occasions, with at least 48 hours between sessions. On the first day, leg-extension one-repetition maximum (1RM) was estimated using Brzycki’s equation. During the second session, lifting trials consisted of one set of 10 repetitions at 60% of 1RM, performed at 15, 30, and 60º/sec, representative of very slow to very fast lifting velocities. Bipolar surface electrodes were used to identify the concentric and eccentric phases of the lift.
Results indicated that no differences in muscle activation for concentric or eccentric phases for the Biceps Femoris existed for all velocities. Significantly greater activation was identified in the Vastus Lateralis, Rectus Femoris, and Vastus Medialis for concentric and eccentric phases of extension at 60º compared to 15º. Additionally, activation of the concentric phase of the Vastus Lateralis at 30º was significantly greater than concentric phase of the Vastus Lateralis at 15º, and the eccentric phase of the Rectus Femoris at 30º was greater than at 15º.
Eccentric activation at 60º may be increased due to a braking effect from higher inertial velocities, similar to plyometric-type training. Along with an increased concentric activation of the quadriceps at 60º due to the shortened time to lift, results suggest that higher velocity resistance training can result in additional muscle recruitment, while using a moderate load for lifting.
Implication. The reactions of muscles differ to similar velocities and loads of resistance exercises. The belief that contracting muscles across the body with similar movement patterns (types of exercise) will produce similar adaptations is wrong. To alter the state of any muscles, each muscle needs to be exercised in the specific manner that will result in the quality of change desired. As was demonstrated with the Biceps Femoris in this study, performing resistance exercises on some muscles could produce no differentiated responses no matter how the exercise is performed. Resistance training effects are specific to the load and velocity of contraction and to the muscles exercised.
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