The Science of Training Load: Finding the Sweet Spot Between Fitness and Fatigue

Fitness and Fatigue – The Intrigue of Training

When trying to improve our athletic performance, understanding and managing training load is paramount. Training load, a multifaceted concept, encompasses both the short-term effects of fatigue and the long-term benefits of fitness. Striking the right balance between these two components is crucial for optimizing athletic performance and preventing overtraining and injury. This post will dive into the intricacies of training load, exploring fatigue and fitness, the methods for measuring and monitoring these concepts, and ultimately how we can achieve our training goals.

Monitoring Fatigue can be tiresome

When we’re evaluating our current status (or current performance ability) the question we are really asking ourselves is “How could we perform right now, if tested, compared to our ideal, optimal performance?” For example, if I asked you to run a marathon two days in a row, you would almost certainly do worse (or at least feel worse) on the second attempt, because you are still sore, tired, and… well... fatigued from the marathon 24 hours prior. When evaluated this way, it’s clear that the effects of the prior day would have an impact that detracts from your optimal performance capabilities.

But, of course, it’s much more granular than that. Nutrition, sleep, stress, recent activities, illness, etc. all play a role in how prepared we are for race day (when we shoot to achieve our optimal performance) (1)(2). Now, some of these elements can be monitored and modified, so we’ll dive in a bit deeper below. (And if you are looking specifically for race day prep tips, be sure to check out Episode 11!).

At this point, you may be thinking “Well I don’t need to perform optimally EVERY day, as long as I rest and taper for race day, then the more work I put in now, the better I will be!” However, I am happy to share that the ideal marathon training is NOT to run a marathon every single day. In fact, overdoing it may be even riskier than doing nothing at all!

Researchers have noted that athletes are at increased risks of injuries and illness as they move toward higher levels of exertion and training load (3). Athletes are more likely to sustain both non-contact injuries, and come down with illnesses when their loads are high (3). Interestingly, according to the ‘open window theory’ (supported by several studies), athletes are at higher risk of getting upper respiratory infections immediately following high-intensity endurance events (such as marathons) due to a temporary decrease in the immune system (4).

Okay, so we established that it’s important not to overdo it, so what can I do to optimize my approach?

Luckily for us, looking at the ‘Trends’ tab on Athlytic we can see a few very helpful sections in guiding our approach to this! 

Recovery vs. Exertion

First, let’s check out Recovery vs. Exertion. This section is geared toward identifying some of the metrics of recent fatigue (perhaps stress, poor sleep, illness, etc. - determined by HRV) and compares it to your levels of exertion that day. This trend offers fairly acute insight into your current training and if you are consistently working harder than your recovery would suggest, you may be putting yourself at the increased risk of injury and illness we discussed above (5).

Training Load

Next, see the Training Load section, comparing Fitness vs Fatigue. This view offers a longer term look at your exertion. Our goal is to see the ‘fitness’ line increasing over time, a sign of successfully getting stronger!

That said, getting stronger and stronger requires several ‘fatiguing’ exercises, as well. While these do increase our fitness over time, we want to be sure that we are mindful of our goals, as well. Here, you should look for dips in the ‘fatigue’ line indicating a successful rest or taper prior to an event or race. This can help you identify whether you are appropriately improving and when you are ready to perform at your best!

Conclusions

“Work smarter, not harder.” Hopefully, this isn’t the first time you’ve been told that you don’t need to treat every day like its race day, or that you don’t need to run a marathon every day. Listening to your body, and making informed decisions based on the data your body provides, can help you make sure that you stay healthy, injury-free, and ensure that all your hard work is worth the effort!

So, rest, recover, train, and gain!

Sources and Further Readings:

1. Pyne DB, Martin DT. Fatigue - insights from individual and team sports. In: Marino FE, editor. Regulation of Fatigue in Exercise [Internet]. New York: Nova Publishers; 2011 [cited 2024 Aug 18]. p. 177–86. Available from: http://www.scopus.com/inward/record.url?scp=84895379589&partnerID=8YFLogxK

2. Halson SL. Monitoring Training Load to Understand Fatigue in Athletes. Sports Med. 2014 Nov 1;44(2):139–47. 

3. Jones CM, Griffiths PC, Mellalieu SD. Training Load and Fatigue Marker Associations with Injury and Illness: A Systematic Review of Longitudinal Studies. Sports Med. 2017 May 1;47(5):943–74. 

4. Kakanis MW, Peake J, Brenu EW, Simmonds M, Gray B, Hooper SL, et al. The open window of susceptibility to infection after acute exercise in healthy young male elite athletes. Exerc Immunol Rev. 2010;16:119–37. 

5. Mandorino M, Figueiredo AJ, Condello G, Tessitore A. The influence of maturity on recovery and perceived exertion, and its relationship with illnesses and non-contact injuries in young soccer players. Biol Sport. 2022 Oct;39(4):839–48.