Biomechanical Strength, By: Tony Reynolds, MS, CSCS, YCS II
Part II
Due to the multi-dimensional properties associated with free weights, they have been considered the optimal method for training athletes, yet they are not without fault (Behm, 1988; Garhammer, 1993; Harman, 1994; Ariel, 2001). The goal of many weight-training protocols is to increase power output of the athletes being trained, but research has introduced some of the shortcomings of using free weights during traditional movements such as the bench press. Ariel (2001) discussed how the inertial properties associated with the acceleration and concurrent velocity of the bar and body alignment can change the resistance throughout the range of motion. Since the load present in the active muscles during the bench is subject to both biomechanical leverage and the length tension curve, the muscle experiences maximal tension only during small portions of the lift. Elliot et al. (1989) demonstrated that during 1RM (one repetition maximum) bench press trials the bar decelerates during the final 24% of the concentric motion. During bench presses at 81% of the individuals’ 1RM, the bar decelerates during the final 52% of the concentric range of motion. The aforementioned phenomenon can relate to decreases in bar velocity, reductions in power output, and a reduction in the physiological recruitment of motor units. Essentially strength and power, in conjunction to motor unit recruitment, are emphasized during the initial portions of the concentric phase of the lift, but than taper off considerably during the end of the motion (Sale & MacDougall, 1981). This is contraindicated due to the frequent utilization of the terminal ranges of motions during dynamic activities, and thus these ranges of motion should receive adequate attention.
Many coaches, researchers, and athletes have developed various solutions to compensate for the shortcomings of many weight lifting movements. These solutions include, accommodating leverage machines, iso-inertal machines, compensatory accelerations training (CAT), plyometric training, and contrast training (Behm, 1988; Jesse et al., 1988; Lander et al., 1985; Newton et al., 1995).
Contrast training, a hybrid method developed from accommodative or variable resistance, incorporates the use of heavy elastic bands in addition to free weights. Behm (1998) hypothesized that the use of bands and free weights simultaneously would increase the effectiveness of the lift by complementation. He suggested that this method would allow the shortcomings of each to be augmented by their strengths. The use of elastic bands will create little resistance at the initiation of the concentric portion of the lift but will increase with bar displacement. This increase in resistance will recruit additional motor units to aid in completion of the lift. Behm claimed that the elastic bands would control the momentum of the weights and provide the needed additional or compensatory resistance during the lockout portion of the lift (Lim & Chow, 1998).
Many researchers have examined the effectiveness of eccentric loading and overloading and the concurrent influence on the stretch-shortening cycle (SSC) on the resultant concentric potentiation. Doan et al., (2002) investigated the use of eccentric overloading on the traditional bench press. By using weight releasers that disengage from the bar at the end of the eccentric motion, they were able to increase each subject’s eccentric load by 5% of their bench press maximum. Each subject’s 1RM was retested with the addition of the 5% eccentric load. The resultant data revealed an immediate increase of 5-15 pounds for all subjects involved. From this data, the researchers deduced that the immediate increase in strength must be partial due to the increase of the load-induced stretch in the serial elastic components involved in the SSC.
Research on SSC exercises, or reactive exercise, recognizes that regardless of contraction history, higher levels of musculotendon stretch prior to concentric potentiation results in a greater functional state for the involved musculature. This allows the involved musculature to facilitate greater force generation. Research states that restitution of elastic strain energy, myoelectric potentiation, interaction effects of contractile components with tendinous structures, and chemomechanical potentiation, can all affect the level of stretch-induced gains in muscle function (Bosco, 1982; Cavagna, 1968; Ettema, 1990). Furthermore, the greatest influences of these reactions are experienced during the initial 500 ms of the concentric motion (Jenson et al., 1991; Svantesson, et al., 1994). This research helps confirm that increased activation prior to concentric potentiation can lead to increased excitation for concentric work (Walsh, 1997; Fenn, 1931).
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