LEWIS: Plyometrics Flashcards
Type of training designed to improve
Power
Plyometrics involves high intensity, explosive
Muscular contractions
Plyometric exercises involve bounding, jumping or hopping to make muscle groups work
Eccentrically before a powerful concentric contraction
focuses on engaging the
Stretch reflex
The stretch reflex is a protective mechanism that
Prohibits over stretching of muscle fibres
Any tendency to over stretch is detected by specialised receptors in muscles called
Muscle spindles
When muscle spindles are suddenly activated, a nerve impulse is sent to the spinal chord which results in the immediate contraction of the
Muscle being over stretched
Eccentric contractions occur when the muscle lengthens as it develops tension - these contractions occur during
Downward movements
Concentric = shortening
Occurs during
Upward movements
Plyometrics contraction involves an
Initial rapid eccentric movement
An explosive concentric movement
A muscle that is eccentrically stretched before a concentric contraction will
Contract more forcefully and more rapidly
Plyometrics works as a form of power training because, when a quick stretch is detected in the muscles, an involuntary protective stretch reflex occurs to prevent over stretch and injury - the stretch reflex increases the activity in the muscle undergoing the stretch allowing it to
Act more forcefully
Result = powerful braking effect and the potential for a powerful concentric muscle action
If the concentric muscle action does not occur immediately after the pre-stretch, the potential energy produced by the stretch reflex response is
Lost
The sequence of the 3 phases is called the
Stretch-shortening cycle
3 phases:
1)Eccentric muscle action - elastic (potential) energy is generated and stored in the elastic tissues of the muscle
2)Amortisation - short time between end of eccentric and start of concentric
The shorter this phase the more powerful the subsequent muscle contraction Will be
3)concentric muscle action/Actual muscle contraction, involves an upward concentric contraction which results in improved muscular performance
By utilising the stretch-shortening cycle, movements can be made
more powerful and explosive
Questioned suitability because there is a
Risk of injury
As a precaution to reduce injury it is suggested that performers attempting to introduce Plyometrics do so with a
substantial strength-training background
Injuries are more likely to occur if there are
Depth jumps from TOO great a height
Improper landing
Inappropriate landing surface
Landing surface=important
Should possess adequate
Shock-absorbing properties, e.g. Grass, rubber mats or suspended floor
Plyometrics can improve performance in
Vertical jumping
Long jumping
Sprinting
Sprint cycling
plyometric training uses muscles’ elastic properties and proprioceptors (muscle spindles and GTO) to generate maximum force by:
increasing the recruitment of muscle in a minimal amount of time
The eccentric contraction immediately preceding a concentric contraction significantly increases the force generated concentrically as a result of the storage of elastic potential energy. This extra energy is released as
kinetic energy during the concentric phase
3 mechanism by which plyometric training improves performance:
- Enhanced muscle spindle activity
- Desensitisation of the GTO
- Enhanced neuromuscular efficiency
Enhanced muscle spindle activity: (SET THE MUSCLE TO A PRESET LENGTH) when muscle spindles are stretched the muscle spindles are also stretched. This causes the spindles to send nerve impulses that result in reflex contraction of the stretched muscle. This reflex enables the muscle to
rapidly return to its preset length
Desensitisation of the GTO: Repeated plyometric exercises desensitise the GTO by increasing the degree of stimulation needed for the GTO to inhibit muscle contraction. This means that:
the muscle can produce more force
Enhanced neuromuscular efficiency: May promote better coordination of contracting agonists and synergists, thus improving the efficiency of the CNS, Making use of the stretch reflex, inhibiting the GTO and enhancing the ability of the nervous system to react to the lengthening muscle optimises the
force produced by the concentric contraction
Plyometrics improves jumping ability, running economy and power output but not:
improved strength
