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If you are working in the elite sporting arena with elite athletes as a Physical therapist, sports physician, doctor, athletic trainer or strength and conditioning coach, chances are that you have read something lately on Load Management or The Acute to Chronic Workload Ratio. If you haven’t, you need to continue reading this blog and start changing the way you go about training and managing your athletes. If you don’t work in the elite arena, you are excused for not hearing about it. But you still need to read this blog…
Load Management is a VERY interesting topic at the moment in sports science and sports medicine circles, and there are numerous studies published on the topic in sports such as Soccer, Aussie Rules, Rugby Union, Rugby League and Cricket.1,2,3 Regardless of the sport you’re involved in, and regardless of the level of play (i.e. professional or amateur), the principles of Load Management can and should be applied to all your athletes and patients, from the professional elite athlete to the sedentary office worker.
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 in one week, you would have a weekly load of 2100 units.
From the current research, the evidence-based way to quantify “load” is by using the concept of the Acute to Chronic Workload Ratio (ACWR). It is number based, so I’ll try to keep it very simple:
- Acute workload = sum of load across a rolling 7 day period i.e. 5 days of exercise x 420units per session = 2100 units.
- Chronic workload = average of the acute load over a rolling 4 weeks i.e. 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, 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 “danger zone”, 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. 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 some ACWR values and their chance of injury. 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 health professionals working with patients/athletes who are training/working hard is that you don’t necessarily see 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, we can reduce the risk of injury when unavoidable spikes occur and minimize the chance of injury. For example; extra-time in a game of soccer, or when you get called up to play an extra 2 games of social basketball in a week when you normally play 1. 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:
- If unavoidable spikes in training occur, do not 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.
- 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.
- 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.
Opinions expressed by physiogramworld contributors are their own.