Runners? Check. Playlist? Check. Dry weather? Check.
You’re all set for a great run, but just as you hit your stride, those dreaded shin splints arrive. Sound familiar?
Running is a great way to build fitness, manage weight, and enjoy a regular burst of feel-good endorphins. But all these positive gains can be forced into a holding pattern if you are one of the 13–20 per cent of runners who develop shin splints, also known as medial tibial stress syndrome (MTSS).
What causes MTSS?
Given how common MTSS is, it may be frustrating to learn that the jury is still out on its exact cause. The most popular theory is that as the foot strikes the ground, repetitive loads transferred to the tibia (shinbone) cause bone stress along its inner border. Another theory is that the pain is due to traction along the sensitive lining of the bone, called the periosteum, from the pull of the exercising calf muscles that attach there.
How do I know if I have it?
MTSS presents as pain felt over a length of at least 5 cm along the inside border of the tibia, at the muscle-bone interface. The tender area is typically in the lower third of the shin, and there may be swelling of the soft tissues over the bone itself. If you push down slowly but firmly over the skin, your fingertip may leave a depression. The pain may ‘warm up’ and improve as you continue to exercise, only to recur afterwards, and can ache into the next morning.
Who is most at risk?
One 2015 meta-analysis looking at more than 100 potential risk factors for MTSS found four key predisposing factors:
1) Higher body mass index (BMI): People with a high BMI were more likely to suffer from MTSS, irrespective of the proportion of muscle versus fat contributing to their total weight. It’s thought that the heavier loads transferred to the tibia cause increased bone stress and overstimulation of the sensitive periosteum lining the bone.
2) Flat feet or excessive pronation: A more mobile foot that rolls in as weight is transferred onto it limits the tibia’s ability to rotate inwards and dissipate impact forces, thereby subjecting the tibia to higher repetitive stresses.
3) A greater degree of ankle plantar flexion: This increased range of movement (when pointing your foot like a ballerina) was a surprising risk factor, and a few theories on its role in MTSS have been postulated. One is that these runners are more likely to strike the ground with their forefoot, and so put greater strain on the calf muscles that hold the heel off the ground. Weakness of the anterior calf muscles may also play a role.
4) A greater range of outward hip rotation: This increased hip mobility (when sitting cross-legged on the floor) is thought to alter the transfer of loads from the femur to the tibia, putting increased stress through the tibia’s inner aspect.
Other factors associated with MTSS include being female, increased calf girth, and having less than 5 years of running exposure.
Can it be prevented?
The good news is, MTSS can be prevented for the most part. Stick to running on level grass, gravel or synthetic track, and avoid hard bitumen and hills. Replace worn runners and invest in shock-absorbing inserts. Don’t forget about good nutrition, which is essential to fuel your body and maintain healthy bones.
When commencing or returning to a running program, it’s best to ‘start low and go slow’. Your bone is constantly remodelling and adapting to the loads you subject it to, so ease into your running program by alternating walking and jogging intervals over a manageable distance, and sticking to 2–3 runs per week. The bony adaptations occur during the recovery phase, so avoid weight-bearing impact exercise two days in a row, although you can certainly cross-train on these days with a swim, cycle or yoga class.
If you have flat feet or excessive pronation, don’t hand in your runners just yet! First, ensure you have appropriate footwear with arch support and cushioning insoles. You can also do a strengthening program to train the small muscles in your feet to provide greater stability. An easy starting exercise is to sit in a chair with a towel stretched out along the floor in front of you. Place your foot on the towel with your heel at the end closest to you. Now use your toes to scrunch the towel up and drag it under your foot, trying to pull the whole towel underneath your foot so that you gradually reach the far end. Once you get these intrinsic foot muscles strong, you need to work on endurance. A sport’s podiatrist or physiotherapist can help by providing a progressive strength and endurance program.
If you have a greater range of ankle plantar flexion, you can do exercises to strengthen the calf muscles, as well as stretching and massage to restore normal resting tension in the muscles. For increased hip mobility, you can strengthen the muscles that control the hip joint.
If all else fails and MTSS symptoms do develop, make sure you see your local sports physiotherapist or sports physician, who will be able to help you get back on your running feet.
Dr Bianca Scotney (Sport and Exercise Medicine Physician) is part of the team at Olympic Park Sports Medicine Centre.
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