Running is one of the most popular sports in our modern society, with recreational runners accounting for the majority of participants. The ease of running makes it a very popular sport – all you need is a pair of running shoes and you are good to go. The health benefits of running are well known, which include stress relief, reduced risk for chronic diseases of health (cardiovascular disease, high blood pressure, diabetes, etc.), and improved levels of fitness. The most common reported negative outcome which is associated with running is injury. There are a lot of possible reasons for injury occurrence in running, but one aspect which is commonly spoken about is running biomechanics. The biomechanics of running are complex, so here we want to highlight just a few key points.
Dynamic forces in various directions are applied though the joints, tendons, muscles, and bones when running. Of particular interest when it comes to running, is the ankle and knee joints, achilles and patellar tendons, as well as the gastrocnemius, soleus, adductor, and hamstring muscles. These forces change with different speeds, as well as with acceleration or deceleration. The different speeds at which we run can be classified as below:
Walking – 0-2m/s
Jogging – 2-4m/s
Striding – 4-6m/s
Sprinting – >6m/s
When running, research has shown that the ankle planter-flexors muscle group contributed most of the force to forward and upward motion during the stance phase. Particularly, soleus is the primary contributor to this force production. Therefore, the calves are an essential (if not the most important) component to high speed running. They can produce forces up to 6-8x bodyweight (BW) in jogging, and 7.5x BW in sprinting. The quadriceps and gluteal muscles seem to play the biggest role in the late swing phase and initial stance phase, producing mostly high negative forces i.e. deceleration in preparing for stance phase. The quadriceps produce forces of up to 4-7x BW in running.
To give an example, if we look at a runner that weighs 80kg, the achilles tendon would need to be able to produce forces of up to 640kg (8x BW). Consider that if this athlete did a single leg calf raise with no weight, that would equate to 80kg (1x BW). Add a 100kg barbell to that calf raise, and you are only at 180kg. Obviously 640kg would be a peak force output, so it is unlikely that you will need to produce this over and over again during running. There is some research that suggest doing around 1.5-2x BW for 6 reps per set is enough to adequately stimulate a compensation response in body tissue to withstand repetitive submaximal loading. In this case, sets of single leg calf raise for 6 reps at 160kg would be enough.
So how does this fit into injuries in runners? We talk a lot about tissue capacity to handle load. Load is a term that vaguely describes various forms of stress and strain. Peak forces, low grade forces, sub-maximal forces, high velocity forces, and repetitive forces are just a few of the various types of loading. Running requires a repetitive low-grade force for an extended period. Increasing the speed of the run (closer to a sprint) would require more high velocity load over a shorter period. Think of a battery. There is a limited amount of stored energy in that battery. Eventually it will run out. Low grade loading will take longer to drain the battery than high velocity loading. Eventually, in either scenario, the battery will run out. This is the same as tissue capacity. Large amounts of low-grade effort (microdamage) will eventually lead to tissue fatigue and failure, resulting in injury. Just as moderate amounts of high velocity repeated efforts will also lead to injury.
You may be wondering why would I run if I am bound to get injured at some stage. Well, there is good news. Injuries can be prevented (although research struggles to prove this for a fact). But we do know that the body is an adaptive organism, ever changing according to the demands placed on it. So, if you just spend some time getting the body to be able to handle more and more load, your chance of getting injured should be reduced (in our experienced opinion). Here are five tips for increasing your tissue capacity to handle the load of running:
- Progressive running overload (volume and intensity)
- Strength training of functional movements associated with running.
- Isolated tissue capacity training specific to running (peak force, high velocity, deceleration, and endurance capacity)
- Running technique is important.
- Incorporate rest in your training schedule to allow tissue regeneration.
Want to know more of some specific exercises and strategies to increase your capacity to prevent running injuries? Our next blog will dive into some of the practical applications. Keep a watch out for the writeup.