Earlier this year I attended the “Mastering Load Symposium” in Melbourne and I found it to be one of the most valuable weekend courses that I have ever attended. The quality of presenters was world-class, and the value of the information delivered was such that it crossed all age groups and levels of sporting ability/fitness levels. For example, unlike a weekend course on the shoulder where you only get to apply your new found knowledge to patients with shoulder pain, load management can be applied to each and every patient/client that walks into your room. Furthermore with the amount of high quality research being published in the area, it is very clear that load management is evidence-based physiotherapy practice, and is – in my opinion – more valuable than manual therapy, and it should be part of every patient’s injury management plan (1).
I could get a bit carried away on this topic and write for days, so for ease of time and ease of reading, I’m going to break load management down into 2 separate blogs, on the 2 most important concepts that I took away from the weekend:
- Part 1 – The acute to chronic workload ratio (ACWR)
- Part 2 – The effect of de-training
I have chosen these 2 topics as I feel that they both spread far and wide, across all age groups, and all sporting codes/physical activities. Before I get too ahead of myself though, I should explain load a little. Load is typically broken down into two variables:
- External Load – eg. distance run, weight lifted, kms cycled/swam, repeated sprints/jumps
- Internal Load – eg. heart rate (HR), rate of perceived exertions (RPE) and/or well-being scores
It usually takes into account training sessions, gym sessions and games. One very simple way to measure load is by using “Sessional RPE” which is:
- Training session time (mins) x intensity (RPE).
- Example: 60 minute training session of 7/10 RPE = 420 units. If you had 5 training sessions like that in one week, you would have a weekly load of 2100 units.
The other way to measure load is by using GPS, if you’re lucky enough to have a few units lying around. Although not as accurate as GPS, heart rate/lactate recordings, Sessional RPE has been found to be highly effective in quantifying training intensity.
The concept of ACWR has been extensively looked at by researchers in AFL, cricket and rugby league(2-4) . Even though it has been largely looked at in professional sports, the principles of it can be applied to the general public of all fitness levels and ages. It is very numbers based, so I’ll try to keep it very simple:
- Acute workload = sum of load across a rolling 7 day period ie. 5 days of exercise x 420units per session = 2100 units.
- Chronic workload = average of the acute load over a rolling 4 weeks ie. assuming that you gradually increase your training loads per week to get fitter; week 1 (2100), week 2 (2200), week 3 (2300), week 4 (2400) = 2100+ 2200+2300+2400 /4 weeks =chronic workload of 2250 units.
- If in week 5 you had a workload of 2500, your ACWR is 2500/2250 = 1.11
- Side note – if you don’t know how many units per week you should be training at, pre-season training in rugby league players showed that players were 50-80% more likely to sustain an injury within a training load range of 3000-5000 units. Now this shouldn’t be used as a blanket “dangerzone”, as each sport and each athlete will have different limits of what load they can handle. So know your athlete, and start to understand what loads they can comfortably handle.
OK, so the ACWR is all nice to know but what does all that mean? Well, researchers have found that there is a “sweet spot” to have a reduced risk of non-contact soft tissue injuries, and that “sweet spot” is a ACWR between 0.8 – 1.3(see image below).
As you can see, the training plan listed above lies within the “sweet spot”.
As you should also be able to see is that with a ratio of 1.11 there is a bit of wriggle room for your training to be increased over the next month to get more out of your athlete. However, if you haphazardly increased the training intensity for week 5 and the load for that week was 5000 units, you would find that you would get a ACWR of 5000/2250 = 2.25 – and your athlete would be in a whole lot of trouble.
Below are the some ACWR values and their chance of injury. If you click on the link above, you’ll see an image of the ACWR and it is interesting to note that 0.8 ACWR has a higher degree of injury risk than 0.8 – 1.3, which suggests that under-training is just as detrimental as over-training:
- ACWR 0.8 = 5-7%
- ACWR 0.8 – 1.3 = 5%
- ACWR 1.3 – 1.75 = 7-10%
- ACWR 1.75 – 2.0 = 10%
- ACWR >2.0 = 15%-20%
So the problem for us as health professionals working with patients/athletes who are training/working hard is that you don’t necessarily an injury during a spike in training. In rugby league players, evidence tells us that the injury usually presents 7-10 days after the spike. In cricket fast bowlers injuries can present as late as 21-28 days later. As a rule, expect an injury between 1-4 weeks after your athlete/patients training has spiked compared to their chronic fitness.
So what is really valuable of being able to quantify training loads and know your patients ACWR, is that we can reduce the risk of injury when unavoidable spikes occur and minimise the chance of injury. For example unanticipated increased bowling workloads in a test match, extra-time in soccer or when you get called up to play an extra 2 games of social touch in a week when you normally play. This is simply done by reduced training load/reduced training time/reduced intensity at training to get your training consistently back in the ACWR “sweet spot” in the subsequent 1-4 weeks.
So there you have it, ACWR in a nutshell. In my opinion, the key messages to take home about ACWR are:
- Don’t increase training loads greater than 10% from week to week.
- If unavoidable spikes in training occur, dont panic! Reduce the training loads over the next 1-4 weeks to get the ACWR back into the “sweet spot”.
- Under-training is just as bad as over-training.
- High loads are not the problem, it is how you get there that is.
I hope I have explained it well enough for you all to understand and given the concept of ACWR justice to the original authors. The next blog will up later this week on the effects of de-training and risk of subsequent injury. As always please feel free to share this blog to people that may find this beneficial/useful, and please let me know if I have missed the mark, or have any questions on this topic.
- Drew MK, Finch CF. The Relationship Between Training Load and Injury, Illness and Soreness: A Systematic and Literature Review. Sports medicine (Auckland, NZ). 2016 Jun;46(6):861-83. PubMed PMID: 26822969. Epub 2016/01/30. eng.
- Hulin BT, Gabbett TJ, Lawson DW, Caputi P, Sampson JA. The acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players. British journal of sports medicine. 2016 Feb;50(4):231-6. PubMed PMID: 26511006. Epub 2015/10/30. eng.
- Gabbett TJ. The training-injury prevention paradox: should athletes be training smarter and harder? British journal of sports medicine. 2016 Mar;50(5):273-80. PubMed PMID: 26758673. Pubmed Central PMCID: PMC4789704. Epub 2016/01/14. eng.
- Blanch P, Gabbett TJ. Has the athlete trained enough to return to play safely? The acute:chronic workload ratio permits clinicians to quantify a player’s risk of subsequent injury. British journal of sports medicine. 2016 Apr;50(8):471-5. PubMed PMID: 26701923. Epub 2015/12/25. eng.
Article by Mick Hughes, Physiotherapist & Exercise Physiologist
Mick Hughes is a Physiotherapist with 7 years experience working in private practice sports physiotherapy clinics.