Article by the Drummond Team
Plyometrics is a fantastic form of training that many personal trainers will have used at some point in their own training programmes at one point or another. It is a key time of year where you may be thinking of including it in many pre-season programmes.
The benefits are widely accredited;
- You burn more calories in a given time,
- You increase the power and strength in the legs which will help all other aspects of training,
- You even enhance neuromuscular facilitation and thus have greater joint stability
These benefits are all benefits we would love to give to our clients, but one question we need to ask is whether this type of training is suitable for our clients?
Before we discuss this let us try and get a greater understanding of plyos:
Fred Wilt, a US long distance runner and track and field coach, is widely credited with coining the term plyometrics – he did so after watching the Soviet track and field team training for their events in the 1980’s. However, Yuri Verkhoshansky created this type of training in the former Soviet Union in the late 70’s and early 80’s, which he called ‘jump training’.
So what is plyometrics?
Plyometric is derived from the Greek word pleythyein meaning, “to increase”. Plyometrics is ‘power training’ by eliciting the stretch-shorten cycle of a muscle fibre it enables a muscle fibre to reach a maximal strength contraction in as short a time as possible. It also improves the proteins in muscle and tendon and increases the passive stiffness of the muscle springs.
The original form of plyometrics developed by Verkhoshansky involved the athlete dropping down from a height bringing about an involuntary eccentric contraction, this is followed by an amortization phase/or rest period, and then an explosive concentric phase as the athlete jumps upward again. The idea is to decrease the time spent in the amortization phase between the landing and the take-off, thus increasing speed and power. The harder and faster that the athlete drops down into the eccentric (pre-stretch) phase, the harder and faster muscle contraction can follow into a more powerful movement.
More recently another type of plyometrics has developed whereby the individual still jumps, but the time spent in the amortization phase is longer and the intensity is much less. This is not truly plyometric in the form that Verkoshansky developed the concept.
In the fitness industry the name plyometrics is often given to all jumps, but not all jumps are plyometric. A jump can be just a jump, if not started from the eccentric amortization phase, landed back into that phase and the elastic energy re-used for the next jump. I often see trainers who advertise a session as plyometric but are just adding normal jumps.
So what makes the difference?
It’s the explosive-reaction from the eccentric contraction that makes it plyometrics. It’s often referred to as the ‘muscle spring’. If you picture a weight on top of a spring when it is still it has no movement power because the spring cannot produce energy only store it and return it. When you apply the force to it and release it its metal coils will use the stored force and return when released. The stiffer the spring, the more economical and powerful it is. Muscles have tow mechanisms involved, one neuromuscular and one biochemical. The myotatic reflex and muscle and tendon passive spring effectiveness.
Myotatic Reflex (neuromuscular)
To get depth into the eccentric phase it involves rapid stretching and then immediate successive contracting of the muscles leading to the muscle power outcome. This improves the function of the nervous system and enhances the neuromuscular relationship and improves the passive stiffness of the muscle spring.
It is the activation of ‘the myotatic reflex’ commonly known as the stretch reflex’ which enhances the given muscle to contract. These are neurons called stretch sensory receptors, which promote a reflex action built into the deep intra-fusial fibres of muscle as a mechanism to tell the muscle to contract if over stretched. For example, when the feet hit the floor from landing from a jump the quadriceps will stretch, a message instantly gets sent to your spinal cord that causes a reflex contraction of the same muscle that is being stretched.
Muscle & Tendon (biochemical)
As a unit, muscle and tendon work on the same principle as the spring. They store and return energy like the metal spring. This can be improved by training to increase the elements that make up our springs and increase their ‘passive stiffness’. In striated muscle this is due to a protein called ‘titin’. titin also known as connectin, is a giant protein that functions as a molecular spring, which is responsible for the passive elasticity of muscle. It is composed of 244 individually folded proteins that unfold when the protein is stretched and refold when the tension is removed.
Titin is important in the contraction of skeletal muscle. It connects the Z lines to the M lines in a muscle sarcomere to which Myosin attach. Titin protein contributes to the force transmission at the Z line and the resting tension in the sarcomere, which in term limits the range of motion in the sarcomere, contributing to passive stiffness of the muscle.
In tendon we have an abundant protein called collagen, which is aligned to produce a thick rope-like connection between muscle, and bone that stores the energy between the two. Training increases the number of chemical cross-links between the collagen molecules, the more there are the stiffer the tendon becomes.
The long-term objective of plyometric training is to increase passive stiffness of muscle and tendon by creating shorter titin molecules and more cross-linked collagen in tendon to make a tighter spring and therefore a more powerful spring and improve the neuromuscular response of the myotatic reflex action.
Exercises can include, sprints, skipping, bounding, depth jumps, hurdle jumps, foot tucks and five-jump tests. The key is quickness when performing them. Not to just jump, skip or bound. You have to move from each jump as fast as possible. This also trains the natural pattern of muscle activation through the neuromuscular response.
What we now need to decide is whether this type of training is suitable for all of our PT clients.
Elizabeth Quinn, Sports medicine guide, notes “Most athletic injuries are caused by forces upon musculoskeletal structures that exceed the structure’s tensile limits”, so therefore we need to start off basic and progress. I.e. not starting with depth jumps or bounding but perhaps building up to these by doing squat jumps and lateral jumps or even skipping.
Dintiman & Ward authors of Running Speed, also add caution. If not implemented correctly and at the appropriate time in a periodised programme they can be dangerous. Injuries include, compartment syndrome, lower back problems through spinal compression, tendon, ligament, knee and ankle injuries. “These injuries are often the result of too many workouts per week, too many jumps per workout, incorrect form, jumping on hard surfaces and using plyometrics at too early an age”. This includes training age.
Muscle develops at a faster rate in a training programme than bone, tendon or ligament. The joint stress through the weight bearing joints is at its highest during plyometric training. Whilst you may have undertaken a period of strength training with a client you have to ensure full joint stability has also developed to withstand the tensile explosive nature of the activity.
If we are taking on a new client who has a very young training age, then I think it is safe to say that this type of training should not be implemented to begin with. We need to know if the client has an injury history or chronic joint pain, if so then this should be avoided completely, but if not and after a period of stability, strength and or endurance training, I believe that plyometrics can be used as a great addition to our toolbox. It can be a fun and punishing way to work your client out. It needs to be included when the client is fresh and towards the start of a session after a thorough warm up, and not at the end of a session as a ‘filler’, but also used sparingly, so plenty of time to recover.
I have heard the following term banded around various gyms; ‘you need to be able to squat 1½ times your bodyweight before you start plyometrics’ – however, skipping is a form of plyometrics and I’m not sure it is correct to say you need to be able to squat over 100kg before you can skip!
There is no doubt about the effectiveness of this form of explosive training if implemented well. Finnish researchers have shown that replacing up to 30% of endurance training with this type of explosive strength training for nine weeks decreases 5k running time in elite cross-country runners by 2.7%(6).
In conclusion, I think plyometrics can be used by PT’s for clients of all abilities, bar complete beginners, but a thorough injury history check and dynamic postural analysis is needed to ascertain whether this is safe or not otherwise training can be completely de-railed and injury the result.
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