What is FATIGUE? And Why We Want to Avoid it at ALL Costs (biomechanically speaking).

"Fatigue" is what you think it is.  It is that feeling of getting tired, so when running, swimming etc things are just starting to get harder and harder. You can't hold your splits, you can't hold your form, or worse, things are starting to get sore.

But for the clinician, fatigue is far more subtle, and less obvious, but waaaaaay more important than you probably realise.

Rule No. 1: "Delay the Onset of Fatigue".

As a movement clinician this is my no. 1 focus when treating athletes, especially those with movement-specific pain. Performance indicators tend to drop, and risks of injury tend to increase with fatigue.

A classic article written in 1991 by Williams et al entitled Changes in Distance Running Kinematics with Fatigue (1) shone a light on the effects of fatigue with respect to running patterns (or kinematics).  The original study looked at kinematic changes for the study group as a whole (under various fatigued and non/competitive environments) and as a whole they found that the effects of fatigue were minimal.  But when they looked at the individuals data, the changes were highly significant in most cases. 

This is still supported when looking over the fairly large battery of contemporary research papers (2) dedicated to this subject: there is NO consistency saying 'with fatigue X will happen'.  There are suggestions that, across a significant proportion of the population, X ( trunk lean angle, hip flexion angles, increases in non-dominant ankle eversion(3)) will happen, but this all depends on the individual.  Which is why I keep saying to athletes, don't try and run like Kipchoge, ride like van Aert, or paddle like Carrington, we need to get you working in the most efficient way we can for you!

What is 'Fatigue', by Definition?

Firstly, and most importantly, 'fatigue' is an inbuilt safety mechanism.  It is there to prevent injury. Makes sense. 

But according to Abbiss et al (4), they start by outlining fatigue in a manner that is relative to the clinician: a Biomechanist considers fatigue relative to force output of a muscle, a Physiologist may define it as failure of a specific physiological system, and a Psychologist may see fatigue as a 'sensation' of tiredness.  

For the purpose of this article, following on with Abbiss' outline, 'fatigue' can be defined as 'sensations of tiredness and associated decrements in muscular performance and function'.  This is more effective for you, because until you get home after your run/ride and look at your Garmin/Stryd data, you won't be able to determine if there were any kinematic changes, just the sensations of tiredness (unless you had a really hard session/race and the wheels fell off). With this awareness of tiredness/fatigue, you can see if there is any correlation to changes in your data.  For the well trained athlete, the likelihood will be low, but as you'll see below, if you're working around an injury this is an important consideration to keep in mind.

Now, I'm the first to admit, one could take this too far and start to panic at the first onset of 'sensations of tiredness', but I'm a very strong advocate of 'scanning' the body when moving, so you can be conscious of where negative changes may come from and therefore this gives you a focus - especially when you apply the strategies outlined below.

What does Fatigue 'Look' Like in Running?

1. NO FATIGUE:

This is a graphic from Stryd, where you can see over the length of the run the cadence (top green line) has stayed perfectly horizontal which shows no lowering of cadence. This suggests the runner has not fallen into fatigue (or is very well trained).

2. FATIGUED:

You can see in this run, at the beginning of the orange arrow (between the two vertical green lines), there has been a sudden increase in power as the runner has clearly put in a conscious effort. Just before line 2, you can see the cadence has suddenly dropped, and power keeps dropping.  From that point onwards there is a very slow, but constant drop off in cadence.  Leg stiffness (blog post here) starts to drop away as well. The runner has 'blown up'.  

Now you don't need a Stryd (although if you're a passionate runner I do suggest getting one), in order to visually see this sort of fatigue effect, but if you're using a Garmin, Polar or similar, it is highly worth while spending the time looking over the data of your training or race runs, to make some 'assumptions' as to when fatigue kicked in. 

As you'll see below, there is a lot of value in an athlete falling into fatigue.  Where I put my foot down and tell an athlete they should avoid being in fatigue, is when coming back from injury.  At least in the acute stages of rehab, as poor movement patterns induced by fatigue may overload the tissue or injury site being rehabbed (talk to your lead health care practitioner about this).

How to Reduce the Effects of Fatigue:

In no particular order, because they're all related: 

1. Efficiency: Know, as well as you can, by getting a gait analysis, swim analysis, bike analysis, where your technique may fall out of 'efficient'. Or (insert self promotional moment here), jump on my Efficient Runner (and very soon Efficient Cyclist and Triathlete) programme so that you can learn how to self analyse your gait. I have always told the athletes I'm assessing, the faults we're finding are an opportunity to get better, so go in to this with a positive mindset.  Therefore, if you know when you're running fatigued you have a tendency to start to do X, then you'll have the awareness to mitigate this change by doing Y. Eg: 'As soon as I get fatigued, I start to 'sit in the bucket'. To manage this I really focus on keeping my hips pushed forward'.

2. Body Scan: In a recent interview with long distance triathlete Patrick Lange, he was saying how he spends a lot of time on the run looking for changes in his running technique.  Top NZ swimmer Lewis Clareburt was being interviewed on Radio New Zealand a few months ago, and he was posed the question "don't you get bored just staring at the black line in the pool for lap upon lap", to which his answer was "no, because I'm constantly thinking about what I'm doing in the moment" (Link HERE) .  A good friend of mine, Moss Burmester (World Champion and Olympic swimmer) says 'practice doesn't make perfect. PERFECT practice makes perfect' to bed in technique. All these strategies create a level of awareness so that you can adjust the technique, or be more resilient with your current technique, even when you know fatigue is there.

• Runners: are your feet/arms crossing over your centerline? Are your shoulders starting to lift?
• Cyclists: are you starting to get heavy on the hands? Are the knees clipping the top tube?
• Swimmers: is the pelvis starting to drop? Are you still rotating well?

3. Build Appropriate Strength: 'Appropriate', what does that mean? Each code has different evidence-based guidelines as to how to build the 'perfect strength'. The fine balance between time spent running/biking/swimming, plus core, plyometrics, and resistance training in the gym, it varies between the codes.  Think of this as locking in technique so as to delay the onset of fatigue. (New blog post coming on swimming soon).

4. Economy: Get a coach, or get an online coaching plan from a reputable coach. Yes, there is a cost, but too many athletes (runners in particular) either do too much, or spend too much time running too fast.  Also, too many athletes don't understand the concept of 'adaptation occurs with recovery', and think more is always better.  So working to a plan that a professional has either created for you, or a generic plan for an event, will put you in far greater stead for reducing the likelihood of an overuse injury, or blowing up on race days due to poor training.

Final Note:

Fatigue has it's place.  As mentioned above, when you recover from being physiologically fatigued, then you will adapt and become a more economical athlete (specificity of training).  Just don't let fatigue change your technique too much so that you fall into bad practices and head down a slippery slope towards inefficiency.

References: 

1. Williams, K. R., Snow, R., & Agruss, C. (1991). Changes in Distance Running Kinematics with Fatigue. International Journal of Sport Biomechanics, 7(2), 138-162. Retrieved Oct 9, 2023, from https://doi.org/10.1123/ijsb.7.2.138

2. Winter S, Gordon S, Watt K. Effects of fatigue on kinematics and kinetics during overground running: a systematic review. The Journal of Sports Medicine and Physical Fitness. 2017 Jun;57(6):887-899. DOI: 10.23736/s0022-4707.16.06339-8. PMID: 27074435.  /  Nicol C, Komi P, Marconnet P Effects of marathon fatigue on running kinematics and economy 1991 

3. Kilblauer et al, Kinematic changes during running-induced fatigue and relations with core endurance in novice runners. Journal of Science and Medicine in Sport. 2014

4. Abbiss, C.R., Laursen, P.B. Models to Explain Fatigue during Prolonged Endurance Cycling. Sports Med 35, 865–898 (2005). https://doi.org/10.2165/00007256-200535100-00004