http://www.kettlebellscience.com/overspeed-eccentrics.html
A method used to increase the intensity of the kettlebell swing or snatch is the ‘overspeed eccentrics’ technique. In addition to the ballistic concentric acceleration of the kettlebell during the forward swing phase, an active acceleration of the kettlebell on the backswing is utilized. Instead of letting the kettlebell accelerate downwards under gravitational forces, the user actively pulls the kettlebell down, or a partner pushes the kettlebell down at the top swing, increasing the speed of the eccentric muscle contraction of the posterior chain. During an eccentric muscle contraction, the muscles lengthen while contracting under tension from the external load of the kettlebell. Research shows that eccentric muscle contractions are capable of producing more force than either isometric or concentric muscle contractions (Komi, 1973) and that maximum eccentric strength is estimated to be between 1.5 and 2.0 times that of maximum concentric strength (Rogers & Berger, 1974)
The ‘overspeed eccentrics’ technique results in an accumulation of kinetic energy that results in greater force production and elastic energy (Thibaudeau, 2004). Farthing and Chilibeck (2003) explain that training programs that utilize eccentric contractions at fast velocities remove neural inhibition, serving as a mechanism for injury protection. This can be explained by the stretch reflex phenomenon. The rapid stretching of the posterior chain muscles in the backswing causes sensory muscle spindles to activate, which are distributed throughout the fleshy part of skeletal muscle. These muscle spindles consist of specialized muscle fibers called intrafusal fibers, which lie within the spindle parallel to the regular extrafusal muscle fibers. Each muscle spindle has its own sensory and motor nerve supply. The sensory neuron that innervates a muscle spindle’s intrafusal fibers are known as gamma motor neurons, whereas the motor neurons that supply the extrafusal fibers are called alpha motor neurons. The intrafusal fibers serve as receptors that are sensitive to the muscle being stretched as well as to the speed the muscle is being stretched (Chu, 1983).
In order to protect the muscle from being over stretched, the message that the muscles are being lengthened is sent to the spinal cord by way of a ‘one synaptic junction’, which causes the spinal cord to act on this information, by contracting the muscle that is being stretched and inhibiting the contraction of the antagonist muscles (Chu 1983), bypassing sending the message to the brain. This is known as the ‘stretch reflex’. Taking advantage of the elasticity of the muscle and the stretch reflex is referred to as the stretch-shorten cycle (Bosco et al, 1981), and it has been shown that the faster the muscle is stretched eccentrically, the greater the force will be on the following concentric contraction (Bosco et al, 1980).
Figure 6.. Muscle Spindle. A stretch of the muscle spindle receptor creates the ‘stretch reflex’ to cause the muscle extending to contract.
In order to take advantage of overspeed eccentrics during the two arm kettlebell swing, two things must be present (i) a fast backswing portion of the kettlebell swing and (ii) a rapid switch between the eccentric muscle contractions of the backswing into a concentric contraction of the forward swing. This technique can be implemented into the kettlebell swing by either having the kettlebell user actively pull the kettlebell down during the backswing, or a partner forcefully pushes the kettlebell down when the kettlebell reaches the top swing.
After a single session of intense eccentric exercise, noticeable amounts of delayed onset muscle soreness (DOMS) are usually present, which can be explained by the increased damage to the myofibrils and connective tissue elements such as the Z bands (Siff & Verkhoshansky, 1998). Friden et al (1983) examined the effects of eight weeks of three sessions per week using eccentric exercise and found that post exercise soreness not only disappeared after 2 to 3 weeks, but the ability to perform eccentric work even increased by 375%. Muscle biopsies at 8 weeks revealed that Z band damage did not take place, signifying that adaptation to eccentric exercise had occurred, suggesting a decrease in injury susceptibility. The training and rehabilitation implication of high velocity eccentric training, applied in a progressive overload manner, may enable the connective tissue to resist high impact forces such as running and jumping (Siff & Verkhoshansky, 1998).
Komi & Buskirk (1972) found that eccentric training produced greater eccentric, concentric and isometric strength increases than did concentric training. Furtermore, Simmons (2007) states that eccentric overspeed training is one of the most effective ways to build explosive and absolute strength when using resistance bands attached to a bar during barbell back squats, however, no studies have yet to be done on this phenomenon during the kettlebell swing.
Комментариев нет:
Отправить комментарий