By Tom Goom (@tomgoom)

Originally posted on RunningPhysio blog

A key concept in preventing and managing running injuries is understanding the balance between training load and your capacity to handle that load. In a nutshell it’s a case of working within your limits and not pushing your training beyond what your body can cope with. Today we look at finding the balance and some important recent research…

The picture above shows a common scenario I see everyday treating runners in clinic; training load outweighs load capacity. They’ve pushed their training on, increased too rapidly and exceeded what their body can cope with. The result, something hurts! Our bodies are amazing, we’re made up of complex, living tissue that constantly adapts to load. Push it too far though and it can’t adapt quickly enough and what we often see is a reactive response. Tendon is a good example of this. When the load on the tissue exceeds its capacity to manage that load it reacts, often becoming swollen, sensitive and painful.

Unfortunately injured tissue’s ability to handle load is usually reduced. Scott Dye covers this nicely with his idea of an ‘envelope of function‘;

Staying with the tendon example, following injury a tendon that used to manage 20 miles or more of running may be painful with even a few minutes. This initial pain settles but it’s still likely that it won’t cope with going back to 20 miles straight away. Its capacity is reduced and will need gradually building up again. This is part of the reason why injury recurrence is common and previous injury is one of the key risk factors for developing further running injuries in future.

Training load

Tissue load is dependent on your training volume (how much), intensity (how hard), frequency (how often) and type. That’s not where it ends though, your other sports, work, habits, hobbies and anything in life that loads tissues all forms part of your overall load.

Loading tissues through sport and exercise is healthy and promotes adaptation such as strength gains, improvements in fitness, and even tissue healing. Problems often occur when tissue load increases too quickly which we commonly see from training error in runners. This graphic neatly summarises the key goal to avoid overloading your tissues, change gradually…

For more on this see our previous articles on injury prevention.

Tissue load capacity

The body’s ability to handle load is dependent on a host of factors including strength, movement control, flexibility, running gait and other biomechanical factors. Recent research by Jill Cook and Sean Docking highlights the importance of improving tissue capacity, not just in the injured tissue but throughout the kinetic chain,

Clinicians need to be thoughtful and skilled in normalising capacity across all soft tissues of the kinetic chain after injury to a single tissue.

Patellofemoral pain is a good example of this. We recognise that several areas from the hip and trunk down to the foot and ankle can influence load on the patellofemoral joint;

This excellent slide is courtesy of @DrChrisBarton, whose recent paper on best practice management of patellofemoral pain highlights the need for education to encourage activity modification alongside rehab that addresses all needs of the kinetic chain. Lack et al. (2015) provides further support for this with their evidence of the effectiveness of gluteal strengthening for patellofemoral pain.

If we can identify which area is key for each individual patient then we can maximise load capacity locally in the injured tissue and in all relevant tissues around it through targetted strength and conditioning.

A combined approach of modifying training and appropriate strength and conditioning is ideal for reducing running injury risk and redressing the balance between loading habits and tissue capacity;

A key concept from Cook and Docking (2015) is that rehab needs to be progressed so the load capacity of the tissues meets the needs of the patient. The picture below illustrates this nicely. They go on to raise another important point, it’s unlikely passive interventions (like massage, manipulation, acupuncture, injections etc) will have long term effects on tissue capacity. They may have some role in reducing pain but, put simply, you can’t massage strength into someone’s legs!

Source Cook and Docking (2015), courtesy of @BJSM_BMJ, reproduced with permission.

More than mechanics!…

Of course though we must remember we are much more than mechanics, and a bundle of tissues responding to load! Multiple personal factors play a part too and must be considered.

Research is starting to explore the role of sleep in injury risk and performance. Evidence from adolescent athletes suggests injury risk increases with less than 8 hours sleep per night. Stress may play a crucial role and has been found to slow healing by as much as 40-60%! Mental health may be a key factor and a positive view of return to sport has been associated with a greater likelihood of returning to your pre-injury level.

Diet and energy availability may also be play a role in injury risk. They have been found to be implicated in the development of bone stress injuries alongside a number of other factors that affect bone load capacity (Warden et al. 2014);

High BMI is associated with increased risk of running injury and has been linked to tendinopathy and plantar fasciitis. Evidence suggests age, genetics, hormonal changes around the menopause, metabolic issues and the use of certain antibiotics may all influence the risk of developing tendinopathy.

All of these factors have a link with tissue load capacity or its ability to adapt to load. Beyond this though we need to remember that pain isn’t just down to changes in the tissues. Pain itself will influence tissue capacity and needs to be addressed as a priority. Our beliefs, values, experience and attitudes towards this pain will all have an influence and can’t be forgotten. For more on this see @DerekGriffin86’s excellent guest blog ‘Why do I hurt?‘. Even the brain itself could potentially influence load capacity. Recent work by Rio et al. (2015)found cortical inhibition in athletes with patellar tendinopathy which reduced following isometric exercise and there’s evidence the brain may play a crucial role in regulating exercise performance.

The take home message here is that our ability to manage load and to train as much as we want to is affecting by a host of factors, all of which need consideration, especially following injury;

Closing thoughts: if you want to reduce injury risk, or plan effective rehab try to balance training load with capacity to handle that load. Sensible training structure with a planned, gradual progression and individualised strength and conditioning can be a powerful combination in achieving this. Remember too though that pain and injury go well beyond just ‘issues in the tissues‘! Consider if stress, sleep or general health concerns may be playing a part. And finally…

…A BIG thank you to @AdamMeakins who very kindly put together this video after our recent Running Repairs course which includes a little on tissue capacity and key points from the weekend. We have more courses coming up in 2016, see our course page for more details.