Abstract
The purpose of the present research was to determine the effects of vibration on motor unit recruitment patterns during muscular fatigue. Eight males (age = 21.4±1.6 yr., height = 69.44 2.62 cm. body mass = 78.06±10.68 kg, body composition = 12.48±2.00%) volunteered to participate. Data collection was divided into three sessions, each separated by a minimum of five days. During the first session, a ten repetition maximum (10RM) was determined for biceps curls (10RM = 16.44±2.47 kg). The second and third sessions consisted of the resistance exercise protocol (10 sets of a 10RM) designed to evoke muscular fatigue. During one of these sessions (V), a vibration (44 Hz) was superimposed by using a custom-designed dumbbell, whereas the other session (NV) was conducted using a traditional dumbbell. Prior to the first set and after each subsequent set, subjects performed a maximal isometric contraction of the biceps brachii at a one hundred and seventy degree elbow angle. During this isometric maximal contraction electromyography (EMG) was utilized to determine maximum EMG, average EMG and the median frequency. At all but one data point, the maximum EMG of session NV were elevated above their baseline readings (pre = 100%, t1 = 116.0±51.4, t2 = 138.6±44.0, t3 = 135.4±48.0, t4 = 110.8±30.9, t5 = 110.5±37.3, t6 = 112.0±45.0, t7 = 116.2±41.7, t8 = 120.5±35.4, t9 = 121.9±39.5, t10 = 110.4±34.3, t11 = 61.9±32.1, p ≤ 0.05). Conversely, maximum EMG of session V was below its baseline at almost every data point (pre = 100%, t1 = 105.9±31.1, t2 = 103.4±40.5, t3 = 101.0±29.5, t4 = 97.7±31.4, t5 = 90.0±28.4, t6 = 98.6±35.8, t7 = 89.9±40.6, t8 = 97.1±34.3, t9 = 93.7±29.7, t10 = 99.9±36.2, t11 = 58.9±20.4). Although the trend for median frequency was not quite as distinct, session V was higher than NV in most instances. It is clear that vibration alters patterns of muscle recruitment with resistance exercise, however, the mechanisms for these observed pattern changes is unclear.
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