Movement Forces Explained: How to Load the Body Functionally in Moving

I've been talking about ‘movement forces’ for 15 years, and I still get blank looks from people when I mention that slowing down from changing direction in an agility drill involves multiple times body-weight.

I remember doing a boxing session with Peter Bridges, he was getting me to throw an efficient left jab, and he asked me to hit him with my body-weight.  In other words my left jab should have had 84kg of force behind it.  When I teach someone to hit a volley, I want them to volley with their body-weight.  The ground gives me the ability to organise the movement, so that I can direct the distal aspects of my body in relation to the task.

In the Sports Science literature, movement forces are usually mentioned along-side injury.  What this tells me is that we do not understand how to utilise the forces inherent in movement very well because movement itself is not understood very well.

This blog will explore the load we produce when we move, so that we can be clear on movement forces as training.  From this clarity we can begin to consider how to apply this in the training we are currently doing.

Movement includes task factors such as type of movement, velocity of movement, and internal factors such as muscle activity.

Load can be defined as the sum of all the forces and moments acting on a body.  The term ‘External Force’ describes the forces which are acting externally to the body.  The term ‘Internal Force’ describes forces which are acting on an internal structure in the body such as muscle, joint, tendon etc.

Types of Force
Impact forces are forces which reach their maximum value earlier than 50milliseconds (ms) after first contact.  Impact forces typically occur during landings.

Active forces are forces which reach their maximum value later than 50ms after first contact.  Typical active forces occur during walking, running, take-off for jumps and during most movements that are not connected with landing.  They are forces which are produced by muscle activity in the field of gravity, brought about in the task.]\

Fig.1. Maximum External Impact Forces at the Ground. From 'Olympic Book of Sports Medicine' (1991)

We can see from Figure 1 (click on the image to enlarge it for ease of reading), that sprinting in spikes involves dealing with 5-7 times body-weight.  The step phase in triple jump can have us dealing with 9-14 times body-weight, and that landing from a rebound in basketball involves 4-6 times body-weight.  Given the magnitude of these forces, how well do you think we are coaching movement in our schools and sports clubs?  Can you see the opportunity inherent in understanding being able to harness movement forces in training?  How do I cool-down from sessions involving big movement forces, so as to re-boot the body and set myself up for long-term adaptation so that tightness is not such a problem?

Fig 2. Maximum External Active Forces including sports activities and trampolining. From 'Olympic Book of Sports Medicine' (1991)

Figure 2 shows that trampolining take-off involves 5-8 times body-weight, so what training opportunities does this afford?

• Continuous tuck jumps
• Continuous low squat jumps, not coming up out of the position
• Continuous hops, cycling the heel to backside
• Spin jumps

It is not difficult to consider how this type of training transfers to moving functionally, while also gaining neurological and metabolic adaptation.

Fig 3. Summary of Internal Active Forces. From 'Olympic Book of Sports Medicine' (1991)

Figure 3 shows the loading at the ankle joint in sprinting is up to 14 times body-weight.  Stair climbing loads at the hip joint are up to 5 times bodyweight, and loads at the tibiofemoral joint from short drop landings are up to 24 times bodyweight.  I remember doing drop jumps with Cathy Freeman in 1999, prior to Sydney Olympics.  She found this type of training very challenging, despite the level of her adaptation from running.  This is because the internal structures of the lower extremity have to deal with absorbing the load while concurrently being asked to produce force by jumping.  Top-level Parkour athletes like David Belle are so impressive as movers because of the incredible adaptation they have from the complexity of their training and the big landing forces they constantly deal with.  I have seen him jump from a 2 storey car park onto a concrete footpath, and absorb the landing easily (see clip).  Imagine the bone density of an athlete such as Belle!

In summary, I have presented a case to show how important it is to understand the forces we generate when we move.

• These forces are ideal for functional training, when one moves with good alignment, stability and coordination.
• Movement forces can be used as training throughout a life span and it is incredibly important that we retain as much function as possible as we age.
• Training on different surfaces bring about different adaptation, this includes trampoline and mini-tramp as training tools.
• Ground contact time is an important neurological adaptation, and we can also use auditory feedback to determine how well we are moving.  Charlie Francis, the coach of Ben Johnston used to send athletes in off the track when their foot-falls became too heavy.  This fatigue is neurological.
• Agility, jumps, hops, landing, rolling, and Parkour activities are both interesting and challenging ways to load and complex training.
• Overspeed training using power-bands creates adaptation by increasing neurological quickness.
• I am now offering Power-Band training as a class for those who want to move better, by using movement as load.

Article by Mark McGrath
www.markmcgrath.com.au