Key points
- Training quickly is a unique stimulus. Whether it’s valuable or not depends on who you are, and what you want from training
- True plyometric training demands ground contact times <200ms and emphasises the “spring” that you see in elite track athletes. “Plyo” training with contact times or force production times >200ms should be conceptualised as “power” training, and is more similar to the qualities a running back needs to break the line of scrimmage, or a lineman needs to block rapidly.
- The key variables to consider when determining “plyo” intensity are: impact momentum of the body, impact velocity of the foot/shin, time on floor, and exit momentum. Remember that momentum is mass x velocity, so impact momentum can be increased by increasing entry speed, or adding weight to the system
1 - What is plyo training
Plyometric training is a vague term, and is usually used to describe two completely different types of training as if they were the same.
When we zoom in on the muscle-tendon unit (MTU) and how it behaves under high speeds and high forces, we see relatively binary behaviour.
When more time is available, and more concentric “pushing” is required, lengthening and shortening across the joint/MTU predominantly takes place through length change of the muscular tissue. We’ll see this when the organism has more than >200ms to produce force.
When less time is available, and more elastic “pop” is required, the overall excursion at the joint will reduce, and will predominantly take place through deformation of the elastic structures within the MTU (tendon, titin filament, fascia). This is literally how a movement becomes “elastic”. Elastic MTU behaviour can only take place when muscle behaviour is isometric, and will be expressed when the system has <200ms to produce its force.
For context, here are some rough averages of the time available to produce force in a series of tasks:
- Heavy lifting: theoretically unlimited, practically up to 7-8s
- Standing vertical jump: 400-600ms
- Running two-foot vertical: 300-500ms
- High jump: 150-200ms
- Long jump: 100-150ms
- Sprinting: 75-120ms
True plyometric training aims to overload the elastic strategy, and therefore has the following qualities
- Isometric muscle state
- Some kind of initial flight/fall/impact
- Very short contact times <200ms
Fast training that fails to meet this criteria is not plyo training, but can be thought of as “power training”. Power training generally seeks to maximise the eccentric rate of force development of the involved muscles.
2 - Monitoring Plyometric Intensity
When we look at models to describe sprint running, we find that the vertical forces produced in running can be modelled by 1) the vertical forces produced by the foot, ankle and shin, and 2) the vertical forces produced by the remainder of the body. Considering sprinting is the most “natural” form of plyometric, we can extrapolate this to safe that the intensity in plyometrics is mostly moderated by:
- the impact momentum of the foot, ankle and shin: how hard the foot attacks the floor
- The impact momentum on the entire body: the speed at which the centre of mass (think hips) hits the floor
The reason we use momentum instead of speed is because momentum includes mass, so this way allows us to consider how weighting plyos affects their intensity.
Using momentum, we know that the change in momentum into the jump vs the momentum out of the jump (mass x takeoff velocity) is equal to the jump impulse. If we divide the jump impulse by the ground contact time, we have the ground reaction force.
Therefore, more intense plyometrics will have
- Greater impact momentum of the body
- Greater impact momentum of the foot, ankle and shin
- Shorter times on the floor
- Greater takeoff momentum
3 - Scaling Plyometric Training
When we combine the above with the knowledge that we must always preserve very short ground contact times to maintain elastic states, we can then deduce that we scale plyos based on impact velocity on takeoff velocity. We can also change between double and single leg (where single leg is more intense)
This is how we create our “scale” of plyo intensity
- Double leg, short contact, submaximal = light pogos
- Alternate leg “bounding”, short contact, submaximal = light bounds
- single leg “hopping”, short contact, submaximal = light hops
- Double leg, short contact, moderate intensity = tuck jumps
- Alternate leg “bounding”, short contact, moderate intensity = medium bounds
- single leg “hopping”, short contact, moderate intensity = medium hops
- Double leg, short contact, high intensity = drop and depth jumps
- Alternate leg “bounding”, short contact, high intensity = intensive bounds
- single leg “hopping”, short contact, high intensity = intensive hops
So basically, we go from light to moderate to intensive “effort”, and we go from double-leg to alternating to single-leg.
Please note that athletes who are not sufficiently “springy” WILL NOT be able to perform “true” plyometric behaviour (contact time <200ms) beyond a certain level, no matter how hard they try. Kind of like heavy lifting, “you’ve got what you’ve got” until you develop further
4 - Programming Plyos
So now it’s really easy to program our plyos.
Low intensity plyometrics can be performed up to 6 times per week, 150-500 contacts per session
Medium intensity plyometrics can be performed 2-4 times per week, 60-100 contacts per session
Intensive plyometrics can be performed 1-3 times per week, 15-50 contacts per session
Where:
- a set of 10 double-leg plyos is counted as 10 contacts
- A set of 10/leg bounds is counted as 15 contacts
- A set of 10/leg hops is counted as 20 contacts
Because the real overload here comes from the entry momentum, ground contact and exit momentum, you can introduce as much variation as you want. However, the more you move outside the sagittal plan, the less intensity you can create. Hence, Lighter and medium intensity plyos can be extremely multi-directional, whilst more intensive plyometrics should focus more on vertical and forwards