Ew… planks. The longest 30 seconds of your life. The bane of your existence, your least favourite word that could leave your trainer’s mouth. BUT – so, so important – why?
To answer this question – let’s get nerdy. Skeletal muscles are composed of fibers, with many different characteristics. One of the most common ways to differentiate between these fibres is based on how fast they can produce force – aka twitch time. Fast-twitch fibres both develop force and relax rapidly, but tend to fatigue more rapidly. Slow-twitch fibres take longer to both develop force and relax, but are much more fatigue resistant.
Each individual muscle in the human body has a combination of slow- & fast-twitch fibres, but the ratio between the 2 differs from muscle to muscle and from person to person.
Take the calf muscles for example. There are 2 primary calf muscles – the gastrocnemius (“gas-trock-nee-me-us”) and the soleus (“soul-ee-us”). The soleus is an anti-gravity muscle. It is ‘on’ at all times due to its role in maintaining an upright posture, and is almost completely made up of slow twitch fibres (80-90% slow-twitch). Conversely, the gastrocnemius muscle (which contains a large amount of fast-twitch fibres) is not often activated, but when ‘turned on’, is meant for propulsion and power.
Lacking sufficient muscular endurance in our slow-twitch fibres is usually how we find ourselves in poor postural positions – which leads to unhappy joints.
Think of the stabilizing musculature of the shoulder – generally referred to as the Rotator Cuff. Imagine that – due to fatigue, the slow-twitch muscle fibres lose their contractile ability. Suddenly, your shoulder joint is required to do a heavy, fast, or reactionary movement – such as catching the stair railing when you trip. That loss of muscular endurance in your slow-twitch fibres leads to increased reliance on the fast-twitch fibres for postural integrity, rather than their main job of explosive, strong movement. As a result, injury risk can increase, and neither fibre type is doing its job well.
Doing muscular endurance-based exercises such as plank holds, push ups, wallsits, pullups, etc… allows for those slow-twitch muscle fibres to do their job well, which also allows our fast-twitch fibres to do their job well. Slow-twitch muscle fibres need sufficient endurance to be able to control and hold a particular joint in its proper position, thereby allowing the fast twitch fibres to perform their job of contracting with a desired amount of force.
This information doesn’t mean that planks or push ups are suddenly going to become easier. However, we hope that this leads to a greater understanding and appreciation towards these types of exercises. And we hope that “planks” is now less of a “bad word” in the gym