Running Twice A Day?

Remember earlier in the year I wrote about how it wasn't really increasing total weekly mileage that caused running injuries. Instead, huge single session mileage increases known as "single-session paradigm" more likely caused injuries. That study (Frandsen et al, 2025) found that large jumps in a single-session distance predicted injuries much better than large jumps in weekly mileage.

The 5,205 runners were followed over 18 months and accumulated 588,071 run sessions. The authors found that instead of keeping your longest run to within 10 percent of your previous longer run, a 10-30 percent increase increased your injury risk by 64 percent. A 30-100 percent increase increased risk by 52 percent while more than 100 percent increase increased risk by almost 128 percent.

To increase mileage safely, instead of running say 10 km at a go, you can run 5 km in the morning and a second 5 km in the evening. Each 5 km run stays well within what your body can tolerate. Instead of doing one run further than what your body can normally handle, you can log more volume by running 5 km in 2 manageable sessions separated by many hours of recovery.

Moreover, a 5 km run definitely feels easier than the last 5 km if you are running the last 5km in a 20 km run. Your running form stays better, you have less fatigue and that second run may feel better after a stressful day at work.

When I used to race triathlons, I can run up to 15 km in the morning and then do another easy 5 km in the late afternoon. It allows me to log 20 km without needing to do all 20 km in the morning.

While it's not mandatory to run twice a day, it's probably one of the simplest and safest way to increase mileage compared to running as many days as you already can. Especially if that is your goal without getting injured.

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

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

Your Workout Today May Trigger A bright Idea Next Week

Picture from Triana et al (2024)

What if I told you your exercise session today can trigger a bright idea next week? That's exactly what a recent study by Finnish researchers found. They tracked a person's brain and behavioural activity for 5 months using brain scans and data from smart phones and wearable devices. 

This research (Trinan et al, 2024) was unusual since few brain scan studies involve such detailed monitoring over months. Using wearable technology in this study was crucial, especially since brain scans (while being useful) only shows the subject lying still for 30 minutes. 

2 distinct patterns were identified by the researchers. A short term wave that lasted under 7 days and a long term wave by up to 15 days. The short term wave reflects rapid adaptations like how focus is affected by poor sleep although it recovers quickly. The long term wave suggests more gradual, lasting effects, especially in areas tied to our attention and memory.

The study found that our brains do not respond to our activities of daily living in immediate, isolated bursts. Our brain activity evolves in response to our sleep patterns, physical activity, mood, and respiration rate over many days. This means that your exercise session or a restless night from the previous week can still affect your brain. Hence your memory, cognition and attention can be affected well into the next week.

It is a great study linking brain activity with environmental and physiological data as tracking our brain changes in real time can help detect mental health and neurological disorders early. This allows for earlier interventions and better outcomes.

Even though this study was not focused exclusively on exercise, the results showed that we definitely need a consistent exercise routine and maintain good sleep habits for our overall well being. I find myself particularly sensitive to these as I age. 

Reference

Triana AM, Salmi J, Hayward NME et al (2024). Longitudinal Single-subject Neuroimaging Study Reveals Effects Of Daily Environmental, Physiological, And Lifestyle Factors On Functional Brain Connectivity. Plos Bio. DOI: 10.1371/journal.pbio.3002797