The Biomechanics of strength 1: Power and Strength!

There is a deep dark hidden secret in the world of powerlifting. A secret that no one wants to discuss and is one that is spoken about in the hushed, deep, dark corners of the powerlifting and strength communities on the internet. We will share this secret with you… If you promise not to tell anyone else, OK?

The secret is the sport of powerlifting is not actually powerlifting at all but should, by the definition of the word, be called strength lifting. As you will see in this article, we are going to discuss and dissect the distinct meanings the term ‘power’ has in the world of physics and also biomechanics, and when we consider the goals of a sport it is important to consider the roles that biomechanics plays. Biomechanics is fundamentally the study of human movement and can be broken down into several areas. The two main ones are ‘sports performance biomechanics’ and ‘clinical biomechanics’. In our next article in the series we will discuss exactly what biomechanics analysis of strength sports can offer us in terms of practical, useful information to help improve performance and reduce injury risk, plus exactly how researchers go about collecting this information.

Before we get on to the nitty gritty of biomechanics of the individual lifts many of us perform such as the squat, deadlift and bench press (which will get the attention they deserve in due course), it is important to understand some of the basic terms of biomechanics to aid in our understanding of the research, and also understand why our dirty little secret exists. So with that said, let’s start with the concept of power.

In the purely physics sense of the word, ‘power’ is a function of the amount of work done in a SPECIFIC AMOUNT OF TIME and is calculated by the equation work/distance. We have highlighted the words ‘specific amount of time’ here for good reason; if we consider any lift for powerlifting, the speed at which the lift is performed is not an indicator of whether the lift is successful, simply that we complete a lift over a set distance to the required standards. It is certainly true that if two people both lift the same weight over the same distance and one lifts it quicker, they are generating more power, BUT this is not reflected in our totals. One give away sign that things are not quite as they seem is that totals for a competition are given in kg/lbs, and the unit of power is expressed as joules per second. In sports performance terms, power is related to the capacity to produce muscle contractions at a maximal rate and this is where strength enters the equation, literally as power is a function of both strength and speed.

The amounts of work we do which is an important factor in power and is the force produced multiplied by the distance you move it.                    Work is starting to sound a little closer to the mark in terms of what powerlifting actually is, but is still reliant on the factor of force. So maybe it should be called ‘force’ lifting which would be to the delight of the Star Wars fans out there!

Unfortunately, this is not quite the case. Force is calculated from the weight of an object multiplied by the acceleration of that object. Remember, acceleration is NOT speed or velocity, it is a change of velocity. If we consider a bar on the floor, the force required to lift it requires a change in the bars position – we have to get the thing off the floor. Weight is actually given in Newton’s and is a force; To calculate this, we take a mass and multiply it by 9.81, which is the influence of gravity, to attempt to accelerate the object towards the centre of the earth. Our mass is the same everywhere, our weight changes dependant on how much gravity is acting on us!

Therefore, as we lift the bar and the bar moves from having zero acceleration to some movement away from the floor, we have managed to exert a force on the bar from our muscles that can overcome the mass of the bar under the influence of gravity! This is important to note, as this does not mean if we can’t perform a lift we are not producing muscle force (internal forces), it means that we cannot produce enough force to overcome the external load or forces.

Let’s imagine two competitors lift the same mass of say 200kg (this equals 200*9.81 = 1962 Newton’s… Sounds more impressive doesn’t it!) over the same distance of 1m (lets imagine they are exactly the same height and same technique), but the first lifter takes 1 second to complete the lift and the other takes twice as long. The acceleration of the first lifter is twice that of the second (Lifter 1’s acceleration = 1m/1s=1ms, Lifter 2 = 1m/2s=0.5ms) therefore the force produced during the lift is actually twice that in Lifter 1 vs. Lifter 2, but the same result! So Lifter 1 produces a force of 1962N (1962×1) whilst our second lifter produces a force of 981N (1962×0.5), but with the same total weight lifted!

So we are not quite ‘force lifting’, but getting closer to the mark! In sports science terms then, what we are fundamentally talking about is the concept of strength, but even that has its own distinct definitions and subcategories. Absolute strength is the maximum amount of force a person can exert with their whole body, relative strength is the absolute strength in relation to bodyweight, and strength endurance is the ability to overcome resistance continually. As you can see, powerlifting should be called ‘absolute’ or ‘relative’ strength-lifting, although this doesn’t have quite the same ring to it! On a final note on this subject, I’d recommend that you do not start a petition to change the name of the sport of powerlifting because in fact, in a lot of situations, strength and power are very closely related, so we don’t need to worry too much about semantics. Interestingly Strong Man is actually very appropriately named as it uses many of the different types of strength, including maximal, explosive and strength endurance across its numerous events.

The take home message from this article is to be aware of the factors that are involved in strength sports and to give you practical insight into how we can use physics to define how we interact with our external environment. Once we start to see how external loads affect the body and the different demands that sports have, we can use this knowledge in combination with our understanding of physiology and anatomy. This aids our understanding of the internal forces generated within the body to cope with sporting demands; This can be useful as it can tell us a whole host of things about performance and injury which can then guide training and injury prevention/rehabilitation programs. In the next article we will discuss how we measure movement, loading, and what this information can be used for in the context of strength sports.

Team TTC