How Much Running Is Too Much?

I had a patient earlier this week who's an ultra runner. She did an ultra race in December last year and then took 3 weeks off running. Her first run back was a 20 km run and she started having left knee pain since.

I told her about an interesting article I read last week about the "single-session paradigm" for running injuries (Frandsen et al, 2025). 

The study tracked 5,205 runners over 18 months. Their average age was 46 years and 22 percent of the runners were females. The runners accumulated 588,071 run sessions via the Garmin GPS watches during the study period. The researchers were interested in self reported running related overuse injuries rather than traumatic injuries.

The runners were categorized into training load "spike" states. If mileage was <  10 percent increase, it was categorized as regression. A small spike would be greater than 10 but less than 30 percent increase. A moderate spike would be greater than 30 percent but less than 100 percent while a large spike would be greater than 100 percent increase.

Weekly changes in mileage using acute : chronic workload ratio (ACWR) - 1 week versus past 3 weeks. Week to week ratio, that is change from week to week were also analyzed.

For the ACWR (weekly changes) and week to week ratio, the study did not find any clear positive association with injury. In fact in some runners, a "negative dose response" was observed meaning a higher ACWR did not always mean more injury.

They found that when there was a spike in running mileage in a single session (rather than a gradual weekly increase relative to the longest run in the previous 30 days, many injuries occurred. This was named a shift to a "single-session paradigm" for running injuries.

This matches exactly with how my patient was injured. No running for 3 weeks, then in her first run back she had her longest run in the past month. The body needs time to adapt, big increases in mileage overloaded her muscles, bones, ligaments and connective tissues.

Please note that this study had runners who self reported their injuries, they were not diagnosed, so we need to be cautious and sensible when interpreting the results. Please do not think 'never increase mileage', it is more about progressing and moderating.

Those of you who are wearing smart watches, other tech devices and perhaps using Strava, note that this study suggests that algorithms that measure your weekly mileage load rations (or ACWR) may be under calculating risk. Your devices may need to include "single session spike" metrics or at least be able to compare with longest session in the last month.

Whether you train under a coach or are self coached, plan sessions so that large increases in distances are avoided. Or make sure you monitor carefully and plan extra recovery. Do not just tally weekly mileage, look at how the session distances compare to your maximum long run in the past month. Monitor your "David Goggins /monster sessions" that deviate from your regular training.

The average mean age of the runners was 46 and 76 percent were male. Younger athletes and elite athletes may be different. Other than distance, I will also include running pace, prior fatigue levels, surface of run and shoes to be monitored.

For healthcare professionals working with ultra runners, you can educate them about the single session spikes having higher risk than weekly totals, like I did with my patient. Ask them in detail about their training regime and pay close attention to the longest run in the recent 30 day window.

Reference

Schuster Brant Frandsen J, Hlme A, Parner ET et al (2025). How Much Running Is Too Much? Identifying High-Risk Running Sessions In A 5200-Person Cohort Study? BJSM. 59 (17): 1203-1210. DOI: 10.1136/bjsports-2024-109380

Should Youths Run Long Distances?

Picture by Richseow from Flickr

I had a friend ask me on Thursday if his friend's kids should come in to our clinic for physiotherapy or sports massage as they were complaining of feeing 'tight' in their muscles. This year, some of the National School Games are allowed to proceed (after being called off because of Covid-19 last year), so many school athletes are competing again.

I do not recall having such privileges during my time. Perhaps we were hardier or maybe ignorant about recovery and whatever help you can get from sports medicine/ physiotherapy. Besides, I was never into running high mileage during my school days. There were other teenage runners who mentioned that they clocked 100 km a week, while I seldom got above 30 km. We did a lot of quality intervals rather than quantity. Definitely no junk miles. Preparing for the GCE 'A' levels did not leave us much time to run that much either.

There have been studies of youth athletes (not specific to runners) that show sport specialization makes them more prone to injury. Especially those who played their primary sports for more than eight months in a year. These youth athletes had more overuse injuries in the upper and lower limbs compared to those who spent less time in their primary sport.

Youth athletes who participated in their primary sport more hours each week than their age in years had more injuries of any type. They were also more likely to have a history of overuse injuries if time spent training exceeded recommendations for their age. Hence it is important to do different sports for youths. And not to push them.

A running specific study on track and cross country events (989 girls and 1022 boys between 12-18 years) found that youth athletes who specialized had more overuse and previous injuries of any kind compared to those who did not specialize (Post et al, 2017)

Another study (of 126 female cross country and distance track and field athletes) found an increased risk in those runners who specialized compared to those who did not (Rauh et al, 2018).

In order to reduce the risk of running related injuries in the youth runner, we must take into account the complex interaction of various factors, including growth related changes unique to this population. A summary of the risk factors are in the table below taken from Krabak et al (2021).

In addition, the following recommendations are based on expert opinions in the study by Krabak et al (2021). A musculoskeletal screening on your youth athletes for previous injuries, menstrual dysfunction (girls) biomechanical concerns and training errors.

Youth runners should take part in high impact and multidirectional activities focusing on control of the back, hip and lower extremities through puberty to reduce injury and promote bone health.

Make sure your youth runners have at least one rest day a week, 1-2 weeks off every 3 months and limit participation to less than 9 months each year. Single sport specialization should be discouraged until they pass puberty.

Self motivated youths can be allowed to take part in long distance events if they follow an acceptable supervised training program, maintain normal growth in height and weight and are healthy with good nutritional intake.  

So all physical education teachers, coaches and parents, if your youth athlete has BMI < 17.5kg/m2 or body weight below 85 percent of normal for their age, bone density scores of Z > 1.0, untreated eating disorders, high risk stress fractures (in femoral neck, proximal tibial or navicular bone) and female runners without menarche by 16 years old or less than 6 menstrual cycles in the past 12 months then they will require further medical evaluation.

References

Krabak BJ, Roberts WO, Tenforde AS et al (2021).Youth Running Consensus Statement: Minimising Risk Of Injury And Illness In Youth. BJSM. 55: 305-318. DOI: 10.1136/bjsports-2020-102518.

Post EG, Trigsted SM, Riekena JW et al (2017). The Association Of Sport Specialization And Training Volume With Injury History In Youth Athletes. AJSM. 45: 1405-1412. DOI: 10.1177/0363546517690848.

Rauh MJ, Tenforde AS, Barrack MT et al (2018). Associations Between Sport Specialization, Running-Related Injury, And Menstrual Dysfunction Among High School Distance Runners. Athl Trg Sp Health care. 10: 260-269. DOI: 10.3928/19425864-20180918.

Overuse Injuries? Or Is It Related To Your Training Load?

Picture by richseow from Flickr

A pair of physiotherapists from the Australian Institute Of Sport (AIS) has suggested that overuse injuries are not caused by how much you train but rather by how your training load changes.

They found that comparing your total workload in the most recent week to the rolling average of the last four weeks of training could predict how likely you were to get injured. The term they used was acute versus chronic training load ratio. They suggest that a ratio above 1.5 is a risk factor for injury.

Consider another study done on a group of elite Australian Rugby League players (St. George Illawarra Dragons) for two seasons.

The players' training load was measured using GPS to track how far they ran during training sessions and games. Interestingly, more training did not seem to correspond to greater injury risk, even with back to back matches with less than a week of recovery. They actually found that players with a high chronic (four week average) workload of running 18.9-22 kilometres were less likely to get injured compared to those who trained less.

However, when they measured acute : chronic load ratio, players with a ratio above 1.6 (increasing training load by 60 % compared to their weekly average over four weeks) were far more likely to get injured. A ratio above 1.2 also put the players at risk, but less than those above 1.6.

Let's say you run 50 km a week consistently but suddenly this week you bump it up to 75 km (acute : chronic ratio of 1.5). You have just increased the chances of injuring yourself.

Or if you normally run 50 km a week but due to illness, work or travel commitments missed some training for a month or two and then decide to run 50 km a week again. That increase in mileage also increases your acute : chronic load ratio. So that is actually a training load error and not an overuse problem.

So if you had to take some time off training and want to resume training again remember to ease back into your training otherwise your acute : chronic training load increases and so will your chances of getting injured.

References

Drew MK and Purdam C (2016). Time To Bin The Term 'Overuse Injury': Is 'Training Load Error' A More Accurate Term? BJSM. DOI: 10.1136/bjsports-2015-095543.

Hulin BT, Babbett TJ et al (2016). Low Chronic Workload And The Acute:Chronic Workload Ratio Are More Predictive Of Injury Than Between-match Recovery Time: A Two-season Prospective Cohort Study In Elite Rugby League Players. BJSM. DOI: 10.1136/bjsports-2015-095364.