Plyometrics
This blog is a training resource intended for individuals (e.g. coaches and athletes) wishing to gain more information on plyometric training in relation to sprint performance. Plyometrics is a type of exercise or training; it is based upon producing fast, powerful and explosive movements. Coaches around the world use it to help improve speed, acceleration and power therefore ultimately improving sports performance (Lyttle, Wilson, & Ostrowski, 1996).
Plyometric training has been highlighted as one of the most effective methods of improving power to date; it also does not require expensive equipment and as there are many different forms of plyometric training to suit individual needs and training goals (Ronnestad, Kvamme, Sunde, & Raastad, 2008). Plyometrics can be used for lower body, upper body, and core power development (Potach, Katsavelis, Karst, Latin, & Stergiou, 2009) athletes and coaches alike can use this resource to guide and expand knowledge to further improve training methods. Within the resource there is evidence based data and information that can help enable coaches and athletes to acquire new skills and improve existing ones to assist in improving sprint performance.
How does this work?
Stretch Shortening Cycle (SSC)
Human body segments are periodically subjected to impact or stretch forces. Sprinting is a typical example in human locomotion of how external forces (e.g. gravity) lengthen the muscle. The muscle is acting eccentrically during this lengthening phase, followed then by a concentric (shortening) action. The mixture of eccentric and concentric actions forms a natural type of muscle function called the stretch–shortening cycle or SSC (Komi, 2003). Stretching of an activated muscle prior to its shortening enhances its performance during the concentric contraction (Bosco, Tarkka, & Komi, 1982).
Figure 1. In human walking, hopping and sprinting significant impact loads occur when contact is made with the floor. Preactivation is required from the lower limb extensor muscles before the ground contact to enable them to resist the impact (a) and the active braking phase (b). The stretch phase is followed by a shortening action (c) (Komi, 2003).
Phase
|
Action
|
Physiological Event
|
(a) Preactivation
|
Stretch of the agonist muscle
|
· Elastic energy is stored
· Muscle spindles are stimulated
|
(b) Amortization
|
Pause between phases (a and c)
|
· Type 1a afferent nerves synapse with alpha motor neurons
· Alpha motor neurons transmit signals to agonist muscle group
|
(c) Concentric
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Shortening of agonist muscle fibers
|
· Elastic energy is released from the series elastic component
· Alpha motor neurons stimulate the agonist muscle group
|
Figure 2. Table highlighting the physiological events that take place during a long jump. (Potach & Chu 2000).
Figure 3. Mechanical model of skeletal muscle function (Potach & Chu 2008).
The mechanical model highlights that elastic energy in the musculotendinous components is increased with a rapid stretch (Lycholat, 2004). When the series elastic component (SEC) is stretched it stores elastic energy which then followed by a concentric muscle action is released increasing the total force production (Potach & Chu 2008). The contractile component (CC) (e.g. actin, myosin and cross bridges) is the main source of muscle force during concentric muscle action (Vande Broek, Van Leemputte, Aadries, & Donne, 2009). The parallel elastic component (PEC) (e.g. epimysium, perimysium, endomysium and sarcolemma exerts a passive force with unstimulated muscle stretch (Lycholat, 2004). Hill (1970) described the model as being like a spring which wants to return to its natural state/length. If the concentric muscle action does not immediately follow the eccentric action the stored energy dissipates and is lost as heat this is also the case if the eccentric phase is too long or requires too large a movement around the joint (Potach & Chu 2008). With training the total force produced can keep increasing therefore increasing power which is an instrumental factor when sprinting (Ronnestad, et al., 2008).
Neurophysical model
The neurophysiological model of plyometric exercise incorporates the stretch reflex. When a quick stretch is performed and detected in the muscles, a protective, involuntary response occurs to prevent overstretching and injury, this involuntary response is called the stretch reflex (Bosco, Viitasalo, Komi & Luhtanen 1982). Activity in the muscles is increased by the stretch reflex when they are performing a stretch or eccentric muscle action; this enables it to act more forcefully, resulting in a powerful braking effect and the potential for a powerful concentric action. It is believed that the neurophysical model (stretch reflex) increases force production during plyometric exercises (Bosco, Komi & Ito 1981).
Figure 4. Picture of the stretch reflex. A reflexive muscle action is caused when stretch reflex is stimulated by the muscle spindles, sending input to the spinal cord via Type 1a nerve fibres. Impulses go to the agonist extrafusal fibres in the muscle after synapsing with the alpha motor neurons in the spinal cord (Potach & Chu 2008).
Researchers think that there is a high probability of both models playing a role in the effectiveness of plyometric exercise (Potach & Chu 2008).
How can I Improve?
Sprinting is a vital component in many different team and individual sports such as: football, rugby, long jump and 110m hurdles (Stefanyshyn & Fusco, 2004). Speed is the most instrumental factor when looking at sprint performance (Baker & Nance, 1999). To increase speed, strength and power needs to be improved (Young & Bilby, 1993). Specific plyometric exercises can help improve strength and power and therefore sprint performance (Markovic, Jukic, Milanovic, & Metikos, 2007). For an athlete to increase their speed they need to increase their ground reaction force, this would shorten their ground reaction time as the athlete would be pushing more force into the ground in each stride; to do this an athlete needs to increase their leg power (Hamill, Bates, Knutzen, & Sawhill, 1983). Drop depth jumps, double leg hops, and split squat jumps have all found to be influential to power production (Adams, O’Shea, O’Shea, & Climstein, 1992).
Drop Depth Jump
The drop depth jump is a plyometric exercise it provides a great base of dynamic power for the majority of sports where sprinting is involved. The main muscles involved when performing the drop depth are: quadriceps, hamstrings, gluteals and gastrocnemius. The joint motions that are involved are: ankle extension, knee extension and hip extension (Shepherd 2010).
Shepherd (2010) explained that for a drop depth jump to be efficient the athlete should complete the jump between 0.5 and 0.7 seconds and only spend between 0.2 and 0.3 seconds in contact with the ground. Elite sprinters produce a large amount of force in a short period of time (Weyand, Sternlight, Bellizzi, & Wright, 2000) as short ground contact times are needed to increase speed, this suggests an athlete needs have fast force production to produce maximal power in the shortest time possible (Nummela, Keranen, & Mikkelsson, 2007). Through the drop depth jump power and leg strength will be improved ultimately increasing speed (Shepherd 2010).
Figure 5. Illustration of a Depth Jump (Men’s Health 2012).
How to Complete
Start Position: The athlete should stand on a solid platform at a height to suit them, the higher the platform the greater the strength component, the lower the height the greater the speed component.
Step 1: Take a small step forward off the platform. Landing through the balls of the feet.
Step 2: Spring immediately off the ground into the air as soon as contact is made with the floor.
Step 3: By swinging the arms in an upward motion, the athlete will propel themselves into the air with more force.
Step 4: Maintain decent posture throughout.
Step 5: Keep visual focus ahead at all times.
(Shepherd 2010).
Double Leg Hop
The double leg hop is a plyometric exercise which develops explosive power in an athlete’s leg muscles which can lead to running faster and more economically over any distance (Purves, 2011). This exercise focuses on building lower body strength whilst elevating the athlete’s heart rate (Bruen, 2011).
Adams, O’Shea, O’Shea & Climstein (1992) explained that the double leg hop, being a plyometric exercise, uses gravity to store energy within the muscles of the leg, this energy produces an equal and opposite reaction by using the elastic components of the muscles. In relation to the double leg hop this is when the athlete comes into contact with the ground releasing a downward force and springing forward into the air.
Figure 6. Illustration of the Double Leg Hop (Rush 2010).
How to Complete
Start Position: Stand upright with feet under hips, stomach muscles contracted.
Step 1: Arms bent at 90 degrees with elbows parallel to each other.
Step 2: Lower hips to 90 degrees whilst leaning forward (Sticking out buttocks).
Step 3: Push through heels to jump forward as far as possible, swing elbows forwards to propel body.
Step 4: Land softly through the balls of the feet, ready to repeat.
(Bruen, 2011).
By repeating the exercise the athlete will be maximising power output and strengthening the muscles in the legs (Adams, O’Shea, O’Shea & Climstein, 1992).
Split Squat Jump
The split squat jump is a plyometric exercise that focuses on the hamstrings, quadriceps and gluteals and is used to develop leg power it is a popular exercise with sprinters and other athletes (Dale 2011).
Turner, Owings & Schwane (2003) found that including split squat jumps in a 6 week plyometric training programme helps to improve running economy and speed in athletes. They suggested that the split squat jump involves the stretch shortening cycle to store and return the elastic energy found in muscles, showing it to be an effective plyometric training technique for leg power and strength and ultimately sprint performance. During the split squat jump the athletes leg muscles are producing high amounts of force making them more efficient (Turner, Owings, & Schwane, 2003).
Figure 7. Illustration of the split squat jump (Edell 2009).
How to Complete
Start Position: Feet together parallel to each other.
Step 1: Take a step forward and bend legs so that rear knee is just above the floor and front shin is vertical.
Step 2: Push up through both feet to jump as high as possible, swinging arms forward to provide upwards momentum.
Step 3: Whilst in air swing legs so that on landing the rear leg is now the front leg (Switch Legs).
Step 4: Repeat.
(Dale, 2011).
Programme Guidelines and Exercise Prescription
Health and Safety
The athlete needs to make he/she is fully warmed up before completing any of the above exercises to prevent any injury occurring as the muscles are not ready for exercise (Crews, 2000). When jumping from a platform it is also important to make sure it is secure to avoid falling. Specific footwear should also be used in accordance to the surface material of the floor to avoid any slips, trips and falls (McKenzie, Clement, & Taunton, 1985).
Guidelines
The athlete should complete each exercise with 4-5 repetitions in each, there should be 4-5 sets altogether. The rest in between each set should not be longer than 3 minutes. Explosive strength qualities have to be enhanced in order to increase power (Potach & Chu 2008) this is why each activity is to be performed at a high intensity.
Progression/ Regression
Dependant on the athletes ability to progress in these exercises, it is suggested that they increase the amount of repetitions and sets they perform. Adding weights to the exercise can also increase the difficulty making the muscles work harder.
If the athlete becomes injured or needs to regress for any reason it is suggested that decreasing the intensity or number of repetitions would be sufficient.
References
Bosco, C. Komi, P, V. Ito, A. (1981) ‘Prestretch potentiation of human skeletal muscle during ballistic movement’, Acta Physiol Scand, 111 (2), pp. 135-140
Bosco, C., Tarkka, I., & Komi, P. (1982). Effect of elastic energy and myoelectrical potentiation of triceps surae during stretch-shortening cycle exercise. Int J Sports Med, 3(3), 137-140.
Bosco, C. Viitasalo, J, T. Komi, P, V. Luhtanen, P. (1982) ‘Combined effect of elastic energy and myoelectrical potentiation during stretch-shortening cycle exercise’, Acta Physiol Scand, 114 (4), pp. 557-565
Bruen, J. (2011) ‘A plyometric workout routine for weight loss’, Livestrong, [Online] Available at: http://www.livestrong.com/article/407313-a-plyometric-workout-routine-for-weight-loss/ (Accessed: 05/05/12)
Chaney, C. (2010) ‘Speed training’, Rush Human Performance, [Online] Available at: http://rush101humanperformance.blogspot.co.uk/2009/02/speed-training-2092009.html (Accessed: 05/05/12)
Crews, L. (2000) ‘Group resistance training: Guidelines and safety suggestions’, IDEA Fitness Edge, 3 (5), pp. 1-6
Dale, P. (2011) ‘List of squat exercises’, Livestrong, [Online] Available at: http://www.livestrong.com/article/516053-list-of-squat-exercises/ (Accessed 05/05/12)
Edell, D. (2009) ‘Low intensity’, Athletic Adviser, [Online] Available at: http://www.athleticadvisor.com/weight_room/low_intensity.htm (Accessed: 05/05/12)
Hill, A.V. 1970. First and last experiments in muscle mechanics. Cambridge, University Press.
Men’s Health (2012) ‘Plyometrics for beginners – jumps’, Men’s Health, [Online] Available at: http://www.menshealth.com.sg/fitness/plyometrics-beginners-jumps (Accessed: 05/05/12)
McKenzie, D., Clement, D., & Taunton, J. (1985). Running shoes, orthotics, and injuries. Sports medicine (Auckland, NZ), 2(5), 334.
Nummela, A., Keranen, T., & Mikkelsson, L. (2007). Factors related to top running speed and economy. International journal of sports medicine, 28(8), 655-661.
Potach, D., Chu, D (2008). Essentials of Strength and Conditioning. 3rd ed. Leeds: Human Kinetics. pp. 414-440.
Potach, D., Katsavelis, D., Karst, G., Latin, R., & Stergiou, N. (2009). The effects of a plyometric training program on the latency time of the quadriceps femoris and gastrocnemius short-latency responses. Journal of sports medicine and physical fitness, 49(1), 35-43.
Purves, L. (2011) ‘Body-weight leg workout for runners’, Livestrong, [Online] Available at: http://www.livestrong.com/article/524203-body-weight-leg-workout-for-runners/ (Accessed 05/05/12)
Ronnestad, B. R., Kvamme, N. H., Sunde, A., & Raastad, T. (2008). Short-term effects of strength and plyometric training on sprint and jump performance in professional soccer players. The Journal of Strength & Conditioning Research, 22(3), 773.
Shepherd, J. (2012) 'The Drop Depth Jump: A plyometric exercise to increase vertical leap and improve jumping ability', Peak Performance Sporting Excellence, [Online] Available at: http://www.pponline.co.uk/encyc/depth-jump.htm (Accessed 05/05/12)
Mechanical Model
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