Not all strength exercises are created equal…
Updated: Mar 5, 2021
We know that strength training can have fast and significant impacts on running performance and injury prevention but why?
What is ‘strength’?
It is usually defined as the ability to exert force but, as usual, context is king as what do we want that ’force’ to do?
If we are wanting to improve performance, then we might want to increase power (P = Force x Velocity) by getting more force into the ground to increase stride length on the flat or height up a slope. The running action is like a ‘stiff spring’, we compress the spring on ground contact and store energy then release it to bounce off.
If injury prevention is the key, then getting our muscles and tendons to absorb more force without damage or losing stability is important.
So how do we get our muscles and tendons stronger?
There are only a few ways….
We can change muscle and tendon ‘architecture’. This could be by increasing the cross section of the muscle or tendon by adding more fibres, by changing the pennation angle (the angle at which the muscle fibres connect to the tendon or altering how the proteins within a muscle fibre cell transmit force to the cell wall and this involves resistance training at greater than 65-70% of a persons 1RM and reps of 8-12 per set.
Or we can improve how fast and how much the muscle fibres fire by increasing the drive through the nervous system, how many fast twitch fibres contact and how fast they do it. This is usually done by lifting heavy weights in 2- 6 reps of less per set, lifting light weights fast as in power exercises like the clean or through plyometrics.
We can also get our muscles better at creating force concentrically (shortening), eccentrically (lengthening) or isometrically (staying the same length) but this needs to be task specific. An example is the use of hamstrings in fast running where they have 2 functions, to lengthen eccentrically as the foot swings forward and to extend the hip isometrically at early to mid-stance.
Alternatively, we can get the tendons to transmit more force by increasing their cross section, improving their isometric strength and convincing the nervous system that they can tolerate high loads. A key mechanism of improving tendon performance is improving the isometric force in the muscle is attached to, a weaker muscle won’t be able to hold still and allow the tendon to lengthen and act like a spring.
Another way is to coordination, within and between muscles by doing exercises repeatedly eg. drills. But these exercises must be ‘task specific’ and must resemble some part of the running action otherwise the brain will be learning a movement pattern that it will not need to use.
Let’s evaluate a common exercise …. the clam.
The clam is an exercise that runners often use to improve their running, believing that it it will improve pelvic stability. It involves concentric contraction of the hip abductors and is anisolation exercise (separates these muscles from the rest of the body) and done lying down
Will it? Let’s apply some tests….
To improve strength by adding more muscle fibres we need to work the muscle at >65 to 70% of 1RM, for between 8-12 times for 3+ sets. Well, in preparation for this blog, I’ve just done a 100 and gave up when I got bored. The clam failed this test.
Can the clam improve neural drive and muscle fibre recruitment? Well, each of my 100 took about 2-3 seconds so no speed stimulus there. If I had been motivated to go to failure, then could have used fast twitch muscle fibres but only when the slow twitch fatigued and so hardly getting more to fire at the same time?
Were the tendons involved having to transmit major loads? Nope. Not even body weight and concentric in nature. Failed again.
Coordination? Isolation exercise so definitely little coordination there. And it’s done lying down so doesn’t resemble running at all. Failed again.
So, why do runners, coaches and Physios love this exercise? Well, it may be of use in really weak individuals and in the earliest stages of injury rehab but for anybody else who wants to improve performance?
So how do other exercises do in this exam?
What about other current favourites?
Body weight squats?