• James McMurray

Why looking at weekly mileage is not enough!

There is one comment you hear at almost all training sessions, races, and any social event where runners are present; “what’s your weekly mileage?”

Sure there are some great reasons why athletes and coaches can look at mileage, it is one of the indicators for the amount of training you are currently doing, it is a good quantifiable value that is easy to measure and monitor progression over time. However, there are many reasons why looking at weekly mileage can be very misleading, and should never be looked at in isolation.

Last month, the Journal of Orthopaedic and Sports Physical Therapy (JOSPT) released an article explaining why athletes and coaching should move away from using weekly mileage in isolation and should start to include other measures to optimize quantifying training load (Paquette, 2020). This article highlighted 3 issues that all athletes and coaches need to be aware of:


1) Other factors in your life that can influence training loads

2) The problems with only using running distance to quantify training load

3) Other alternative methods to quantify and monitor training stress that you can use


Other factors in your life that can influence training loads


Training load is essentially the amount of stress (load) that your running training puts on your body. The more stress, the more likely you are to get injured. Athletes and coaches need to find that fine line between high levels of training to get the best performance and high levels of training that lead to injury. How I like to put it is; the quickest athlete is the athlete who can train the hardest without getting injured.

The issue with this is training load is very complex, there are a vast range of factors that can increase the load on your body. Paquette et al. state that training stress is influenced by external (i.e., application of mechanical load) and internal (i.e., physiological/psychological effort) training load factors.


External factors include:

· Volume (weekly mileage)

· Pace (how fast you are running in each run)

· Type of ground you are running on

· Hill vs flat running

· Weather (heat, cold, wet, wind)

· Other training you are doing, for example weight training

· Other physical activity you are doing


Internal load factors include:

· Level of fitness

· Stress levels

· Quality of sleep

· Diet

· Illness

· Motivation


The problem with only measuring running distance to quantify training load


Measuring running distance alone ignores the other external factors in your training, such as pace, and does not factor the internal factors, such as sleep levels. This can massively misrepresent overall training stress.

For example one week you could run 40miles at a slow pace mostly on soft grass, and the following week you could run 20miles but you have just been sacked from your job and you ran mostly on pavement. If you only monitored mileage, would think you had an easy week, in reality, your body have gone through a higher amount of load which could increase your risk of overloading your muscles/bones/tendons, which could ultimately lead to injury if this was continued for a longer period of time.


Other alternative methods to quantify and monitor training stress that you can use


Monitoring the other external factors can give a more accurate representation of the load you are going through. But only measuring external factors alone, still isn’t enough as it doesn’t take into account the internal factors.


For example. You could do a session in September and aim to run at a pace of 5 minutes per mile. You then repeat this session a month later and try to target the same time. You are however fitter after a month of training, and thus 5 minute/mile isn’t going to get the optimum amount of load on your body. Like wise you could repeat the session again, but this time you have a few G & T’s the night before and only got 5 hours sleep. This time running at 5min/mile might be too much for you in this session.


(I would just like to point out at this moment that overloading your body in one session would not increase your risk of injury significantly, but if this was a trend over a period of weeks/months it will increase your risk)


It is relatively easy to monitor external training load with the use of satellite watches, accelerometers, HR monitors, and software such as Strava or training peaks that can accumulate mileage, running pace, and HR into one algorithm that shows your relative effort level week by week, and the trends over time.



Credit: https://pixabay.com/users/rottonara-596655/?tab=popular


However, measuring internal factors can be a little more challenging. If you are part of an elite training team, or play for a premier league football club, or supported by British Athletics. They can use objective measures that require a little bit pricier equipment such as lactate levels, cortisol levels, VO2 Max testing, and biomechanical measures such as tibial shock, foot strike angle, ground contact time, and leg stiffness.

But how can you measure internal factors as a recreational runner? Well the obvious choice is measuring HR as this will be indirectly influenced by stress levels etc. But another viable option that you can use without spending a whole lot of money is taking a rating of perceived exertion (RPE) after each run/session. An RPE is basically scaling how you felt on a run from 0-10 (or you can use any scale you like, for example the Borg scale runs from 6-20, and has a fairly good correlation with HR and blood lactate levels). It must be noted however, that if you plan on using RPE, you will have to be honest with yourself and consistent with your ratings. This maybe an issue with novice athletes who may find it difficult to rate their effort, because they do not have any previous experiences to compare it too.


So, to clarify so far you have measures for external factors of load:


· Mileage

· Pace

· HR


And you have indirect measures for internal factors of load:

· HR

· RPE


Combining the both would therefore be the most accurate representation of training load. You can do this with the TRIMP method, which stands for TRaining IMPulse. The original version uses training volume (measured in minutes) and training intensity (measured as average heart rate).


For example:

Monday: 60 min at 130 bpm TRIMP = 60 × 130 = 7,800

Tuesday: 30min at 190 bpm TRIMP = 30 x 190 = 5,700

Wednesday: 50 min at 120 bpm TRIMP = 50 × 120 = 6,000

Thursday: 40 min at 170 bpm TRIMP = 40 × 170 = 6,800

Friday: (rest day)

Saturday: 40 min at 180 bpm TRIMP = 40 × 180 = 7,200

Sunday: 90 min at 130 bpm TRIMP = 90 × 130 = 11,700

Total:

Time = 310mins

TRIMP = 45,200

And then you would repeat this each week and compare the TRIMP values. However, as you could probably tell from the values, time has a massive influence on the value, and a long slow run could have more of a ‘load’ than a short quick session that causes lactic acid bursting out your ears.


Another alternative you could use is the modified TRIMP that uses RPE.


For example:

Monday: 60 min at 4 RPE TRIMP = 60 × 4 = 240

Tuesday: 30min at 9 RPE TRIMP = 30 x 9 = 270

Wednesday: 50 min at 2 RPE TRIMP = 50 × 2 = 100

Thursday: 40 min at 7 RPE TRIMP = 40 × 7 = 280

Friday: (rest day)

Saturday: 40 min at 8 RPE TRIMP = 40 × 8 = 320

Sunday: 90 min at 2 RPE TRIMP = 90 × 2 = 180

Total:

Time = 310mins

TRIMP = 1,390

The Acute:Chronic Workload ratio is another method of monitoring load. This looks at the ration between short term (7 days) and long term (~28days) workload. However, it is a more complex concept which will have to be discussed in an article for another day!


This method has yet to be validated, and there is some disagreement in the literature on how accurate it is in predicting injury.


So, what does this all mean James?


If you want to measure the changes in training load throughout your training, you need to consider the external and internal factors. Mileage is only one of many external factors and doesn’t take into account the internal factors of load.

If you want an easy and simple way to measure both external and internal factors of training load, keep on using mileage, but consider how fast you are running, and if your runs include pavement, wind, hills, and accommodate for this. You should also use RPE to keep an eye on the internal factors, if your RPE is high all week, next week maybe it would be an idea to keep it low and cap yourself to a certain RPE in your runs.

RPE is a good quick easy option but it is only an estimate of your training load. It is not a direct measure of the exact load the tissues in your body is subjected to. So, make sure you use it as a rough guide and keep it a little bit flexible.

Thanks for reading

James

Sport and Exercise Health Science BSc

Student Physiotherapist



Reference:

Paquette, M.R., Napier, C., Willy, R.W. & Stellingwerff, T. 2020, "Moving Beyond Weekly ‘Distance’: Optimizing Quantification of Training Load in Runners", The journal of orthopaedic and sports physical therapy, , pp. 1-20.

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