Increasing exercise while staying healthy & injury-free – How much is too much, too soon?

With lockdown in full force and the weather steadily getting better, many of us are doing more exercise than we normally do and due to restrictions of gyms, running and cycling interest has taken off in many homes. This surge in activity has the potential to, for all its many positive benefits, lead to a new injury that could stop us from establishing a healthy routine. 

Typically, our cardiovascular system can develop far more quickly in response to exercise than our musculoskeletal system can. This can lead to being able exercise for longer and more intensely than our muscles, tendons and bones are prepared for, leading to overloads and injuries. 

Doing too much, too quickly, not only impacts our risk of injury, but it also has strong negative implications for our immune health, sleep quality, appetite and mood. 

So how can we structure ramping up our exercise to get us outside, keep us fit and healthy and reduce the risk of injury? 

10% rule #

The rule that’s been around the longest is the ​‘10%’ rule and is the easiest to apply for many of us. 

Increase your activity by no more than 10% week on week. 

For example — if you run 20km in week 1, then in week 2 you can only run 22km. 

https://​www​.very​well​fit​.com/sp…

A sustainable and regular routine can be built this way but it has a number of flaws. 

If you think of it like a calendar week I can run 20km on Sunday and then 20km on Monday and that is same weekly increase as doing 20km Wednesday then 20km on Saturday , but if you have noticed it’s much harder (and potentially raises injury risk) to do back to back days rather than having a few days’ rest. 

It only values the previous week as a reference point for your current week and every week as an independent variable. If you normally cycle 100km per week and then have one week where you can only do 20km, do you have to go back to 22km the following week? You would like to think you could get much closer to your normal amount. 

Individual factors are largely ignored, if you have an existing injury or no exercise background, you will want to be conservative depending on the type of exercise, potentially using less than 10% increases. Conversely if you are in very good health, are young and have a high fitness level, it would stand to reason you could tolerate larger increases (up to 25%) to build your fitness level safely. 

Acute:Chronic Ratio #

In recent years researchers in team sports began to examine these weaknesses and came up with a model in an attempt to reduce injuries. Model proposed by Hulin et al 2014 and developed by Gabbett 2016 looks at the acute:chronic ratio; How much exercise ​‘load’ am I accustomed to typically, versus how much I do on a specific day or week. 

Current weekly exercise load does not exceed my previous 4 week average by greater than 30%. 

The aim is a ratio ​‘sweet spot’ of where we can do more exercise week on week (ratio of greater than 1) to get fitter, but reduce injury risk by not increasing too much (ratio below 1.3). Gabbett’s team found an increase in injury incidence above this 1.3 value. For example – 

• If I walk 70,000 steps, each week, for 4 weeks then my ​‘chronic’ load(average) is 70,000.
• Then on week 5 I do 100,000 steps — this is my ​‘acute’ load. 
• My ratio for week 5 is 1:1.42 — so this potentially puts me ​‘at risk’. 

Gabbett TJ. The training — injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50:273 – 80. 

The theory, while developed for team sports, can be applied to most contexts be it running distance, kilogrammes lifted, steps taken and has number of supporters. 

• Many models use a rolling 7 day average (disregarding the normal Monday-Sunday) removing the issues with specific days of the week. 
• It takes into account the previous 4 weeks (or 28 days, depending on model) training to say what you can handle that current week. 
• It supports the idea that more able athletes (those with higher average exercise averages or ​‘chronic loads’) can tolerate greater increases week to week (acute loads). 
• It reduces the significance of a temporary decrease in exercise – say due to work or other commitments. 

In recent years, a number of key flaws have emerged and led to the model needing to be refined. 

• Hard to determine whether the chronic load itself (being too low) or the acute ratio being too high is the reason behind the ​‘injury’. E.g are you undertrained or overtraining? 
• It assumes activities taking place 4 weeks ago are of equal value to those taking place 2 weeks ago, which would seem very unlikely. If I do 100 press ups on a Monday , it will affect me far more on Wednesday, than it will on Friday. 
• It means that you can get the same ratio a number of different ways (by changing the order of your exercise week) so it reduces the validity of saying what is safe practice and what is not. 
• Most models include the current week in the calculation of the 4‑week average, this inherently reduces the amount of change and underestimates risk. 

EWMA – Exponentially weighted moving averages #

In recent years it has been proposed that there may be a better way to monitor exercise and training to prevent overtraining and reduce injury. Following research by Williams et al 2017, exponential weighting of exercise load can create a more relevant picture by prioritising the most recent amount of exercise in calculating ​‘chronic load’ and a relative decrease in weighting the further back you go from the current day. It makes intuitive sense that the run you did 5 days ago will increase your injury risk more than the run you completed 15 or 25 days ago, but many models don’t take this into account. 

Murray NB, Gabbett TJ, Townshend AD, Blanch P. Calculating acute:chronic workload ratios using exponentially weighted moving averages provides a more sensitive indicator of injury likelihood than rolling averages. Br J Sports Med. 2017;51:749 – 54. 

Calculating seems like a lot less simple now than the 10% model, doesn’t it? #

Well luckily automated services such as Strava and Training Peaks fill this gap automatically when you upload your session. They take your training over the past number of days (up to 42 days) , compare it to your most recent training (7 days), and determine how much load you can handle and if you are excessively ​‘fatigued’.

EWMA still has its flaws in predicting incidence of injury most notably the specific nature of the injury or injury history impacting the incidence. All models also treat each injury as an independent event and attach likelihood accordingly, something that isn’t necessarily true. 

• If you, for example, have dealt with achilles tendon problems in the past, the likelihood of this re-surfacing is potentially higher than the person who has never had an issue, when presented with the same amount of load. 
• Often we deal with small aches, pains and old injuries while exercising, and the subsequent changes in how we move, warm up and cool down will affect injury risk in ways any model will struggle to predict. 

It’s the same reason talking to member of our team about your increase in training during lockdown, or how to plan for increase in the future (e.g. race in the autumn), is the best advice to get as complete a picture as possible. 

Take home messages #

1. Increasing amount of exercise in a random manner can cause considerable issues such as injury, illness, poor sleep, appetite and mood. 
2. There are a number of ways to monitor and increase amount of exercise you do progressively, while reducing risk of problems. 
3. Increasing your activity (distance, time, reps or Kilos lifted) by no more than 10% week on week (10% rule) is a good starting point. 
4. Acute:Chronic ratio, the amount by which the current week of exercise differs from your average week, takes into account more variables but is not without flaws. 
5. Exponential weighting to prioritise more recent exercise, in determining what you can do on subsequent days, addresses more issues and has a number of online programmes and apps that can do the calculating for you. 
6. Your own individual characteristics will play a vital role in any determination of injury ​‘risk’ and speaking to strength and conditioning coach, endurance coach, physiotherapist or sports scientist should be considered in determining which model to use. 

References

Gabbett TJ. The training — injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med. 2016;50:273 – 80. 

Hulin BT, Gabbett TJ, Blanch P, Chapman P, Bailey D, Orchard JW. Spikes in acute workload are associated with increased injury risk in elite cricket fast bowlers. Br J Sports Med. 2014;48:708 – 12. 

Murray NB, Gabbett TJ, Townshend AD, Blanch P. Calculating acute:chronic workload ratios using exponentially weighted moving averages provides a more sensitive indicator of injury likelihood than rolling averages. Br J Sports Med. 2017;51:749 – 54. 

Wang, C., Vargas, J.T., Stokes, T. et al. Analyzing Activity and Injury: Lessons Learned from the Acute:Chronic Workload Ratio. Sports Med (2020).

Williams S, West S, Cross MJ, Stokes KA. Better way to determine the acute:chronic workload ratio? Br J Sports Med. 2017;51:209 – 10.