How Long Does Your Running Shoe Last?

Picture from Run Repeat

Ever wondered how long before you need to change your running shoes? A bit of history on midsole technology. Previously, the midsoles in running shoes were all made with ethylene-vinyl acetate (or EVA). Then Adidas managed to secure (Adidas bought the technology from BASF) their Boost midsole out of thermoplastic polyurethane (TPU) in 2013 which led to many marathon world records falling. In 2017, Nike's super shoe, the Vaporfly, was made of polyether block amide (PEBA) and it is still the current dominant midsole.

Previous anecdotal evidence and hearsay suggest EVA midsole running soles tend to last between 300 to 500 miles (480 to 800 km). There was an older study supporting this information (Cook et al, 1985). The researchers measured shoes shock absorption at frequent intervals between 0 to 500 miles. 

A machine was used to simulate running impact as well as 2 vounteers who actually ran 500 miles (pictured above). The 2 human volunteers show similar patterns compared to the machine (see diagram). Human testing showed that EVA midsole shoes retained 80 percent of shock absorption after 150 miles (240 km) and 70 percent after 500 miles (800 km). The curve then flattens out between 300 to 500 miles which is probably where we get shoe lifespan information from.

More recently, a bunch of researchers teamed up with the brand On and manufactured prototype running shoes that were almost identical (Rodrigo-Carranza et al, 2023). One had the new PEBA super foam while the other had the traditional EVA midsole. 

Shoe testing from Rodrigo-Carranza et al (2023)

Both versions also had a curved carbon fiber plate. They tested the shoes before and after 280 miles (448 km). 22 runners performed a running economy test to measure how much energy they used at a given pace, once in fresh shoes, once with pre-worn shoes. The researchers themselves actually ran 280 miles (448 km) in each pair of shoes to pre-wear them for the research!

The researchers found that the new super foam did lose their powers quicker. In fact they were no better than the traditional EVA midsole when they did. A key finding was that energy consumption while running with the new PEBA midsole shoe was 1.8 percent less than using the new EVA shoe. This strengthens the case that the super foam itself is more important ingredient since both versions of the prototypes had carbon plates in them.

Another key finding was that after 280 miles (448 km), there was no significant difference between the 2 shoes. The EVA did not lose anything while the PEBA super foam shoe got 2.2 percent worse. Please note that not all PEBA foams are created equal. On's super foam may not be totally similar to Nike's and other brands.

I have not converted to super shoes yet as I do not like them stacked too high. Moreover, I currently only run 2-3 times a week and I rotate between 2 to 3 pairs of shoes with EVA and TPU midsoles. I run in them until they start to feel "flat". It is relatively easy to feel especially if one of my other newer pairs still feels supportive by comparison. I usually retire that "flat pair" from running but will still use them for walking. If you're using the PEBA foam super shoes, you may have to change them earlier.

If you are interested, have a look at Run Repeat, where infomation on a huge range of high performance super foams are available. The author, Carlos Sanchez runs 100 km a week and has run three sub 3 hours marathons. Sanchez suggests that shoe foams take more than 24 hours to 'recover' and some foams recover faster than others so you may want to rotate your running shoes to maximise comfort and shoe life.

References

Cook SD, Kester MA and Brunet ME (1985). Shock Absorption Characteristics Of Running Shoes. AJSM. 13(4): 248-253. DOI: 10.1177/036354658501300406

Rodrigo-Carranza V, Hoogkamer W, Gonzalez-Rave JM et al (2023). Influence Of Different Midsole Foam In Advanced Footwear Technology Use In Running Economy And Biomechanics In Trained Runners. Scan J Med Sci Sp. DOI: 10.1111/sms.14526

Is There An Ideal Running Cadence Rate?

Picture from Tracksmith

180 steps per minute seems to be the accepted magic number for cadence (or the number of steps) in long distance running. If you read the old Runners World magazine, you will know that legendary running coach Jack Daniels got that magic number by counting the number of steps the elite runners took at the 1984 Los Angeles Olympics.

This is also part of the 'ideal running form' criteria. It is also a relatively simple quantity to measure and change since it's much easier to tell a runner to increase their cadence than altering than heel strike.When you take smaller, quicker steps, it optimizes your efficiency and minimizes your injury risk by reducing impact on your knees and hips with each step. 

What if you can turn over your legs even faster? Watch the elite female Japanese marathoners when they race, they get close to 200 steps per minute. Does more mean better? What does current research say?

Burns and colleagues (2019) found that running cadence varies greatly. It actually depends on your running speed. Your cadence will differ when doing a track interval session versus an easy recovery run.

They studied 20 males and females who placed in the top 25 male and female finishers at the 2016 Ultra Running100 km world championships. The race was held in Spain and consisted of 10 laps of 10 km each lap along an almost completely flat course. This is ideal to determine if there were any specific characteristics that had an effect on cadence. Data was collected from the smart watches of the runners.

A survey was done after the race via email asking about their age, weight, height, training, racing experience and their racing speed.

Only speed and height of the runners have an effect on each individual runners' cadences. The study showed that when the runners run faster, their step frequency increased. Taller runners also had lower step counts compared to shorter runners. This study found that every extra inch in height was associated with a decrease of just over 3 steps per minute in cadence. A 6 foot tall runner in the race took about 18 steps per minute less than another runner who is 5 foot 6 inches.

Makes sense that longer legs will take fewer steps each minute to cover the same distance. 

The lead author, Burns, finished 5th in the race and included himself in the study. The runners' cadences differed greatly, ranging from 155 to 203 steps per minute. The highest and lowest averages actually finished within a couple of minutes of each other. 

Guess what number came up when Burns took an average of all the runners' cadences? 182 steps a minute. Now, that is really close to the optimal 180.

The study also showed that fatigue had no effect on cadence, possibly due to the very flat course. Even when the ultra runners were in the later stages of the race, they held the same pace from the start. In fact they had even faster step counts near the finish when they ran faster despite being tired.

According to the article, there are only 2 ways to increase your cadence, become shorter (like the elite female Japanese marathoners) or go faster. Bear in mind that everyone has a different optimal cadence. Having a higher cadence (than 180) does not necessarily make you a better runner. 

Burns finds that when he is fitter, his cadence is lower at a certain pace since his steps are longer. When his cadence is faster than normal at the same pace, he uses that as a sign that he needs hill work or speed work to get stronger. 

That is a much better way to use cadence to improve your running rather than aiming for a specific number. Especially when everyone's mechanics are different. It is also a good and simple aspirational goal for runners since many runners overstride and land on their heels, putting excessive forces on their knees. 

Reference

Burns, GT, Zendler JM and Zernicke RF (019). Step Frequency Patterns Of Elite Ultramarathon Runners During A 100-km Road Race. J Appl Physiol. 126(2): 462-468. DOI: 10.1152/japplphysiol.00374.2018

How To Be A Better Trail Runner

Picture by Melvin Lee

Many of my patients are now running on trails, making the switch from running on the road which they say is boring. There are also many more organized trail races world wide, and many of our patients participate in these trail races.

What does it take to become a better trail runner? A recent published study compared elite and recreational trail runners in a series of lab tests and found that the elite runners were more efficient over both hilly and level terrain (Besson et al 2023). As a result, they required less energy to maintain a given pace. They were found to have greater leg strength compared to recreational runners. 

The same researchers found similar results when they compared elite trail and elite road runners. The trail runners had stronger leg muscles and were more efficient on hilly terrain (Sabater et al, 2023)

So, do leg strengthening exercises if you want to run better on the trails. Other than visiting the weights room, you can carry a heavier backpack while climbing stairs or walking/ running up and down stadium steps. I used to wear a weight vest while training for the Oxfam Hong Kong Trailwalker event at the old National Stadium steps. It definitely made the uphill sections easier during the event.

Another pattern that has turned up in studies of hilly running trail races is to keep your effort and not your pace constant. The faster finishers showed greater variability in their pacing. They ran slower (or walked) on the steeper sections and ran faster on the downslopes to make up time (Corbi-Santamariaet al, 2023). 

Most trail runners tend to have a fixed pace and try maintain that regardless of terrain. A more efficient strategy is slow down on the uphills and speed up on the downhill sections relative to your average pace. So don't push harder on the up slopes to keep pace, slow down instead to keep your effort constant. You can run faster on the downslopes to get back the time you lost for those who are racing.

Please bear in mind that there's a skill to running fast downhill, particulary on technical terrain. More so during ultras as more than10 hours of racing makes one very fatigued. Not worth having a catastrophic fall while running downhill.

Are trekking poles useful? Usage of trekking poles can be contentious among trail runners.  Giovanelli and colleagues (2023) tested runners on the steepest treadmill in the world, in their lab. Their treadmill can be set to 45  degrees, at a grade of 100 percent! They found that using trekking poles does not save energy, but they do save your legs. On a hill climb of 20 degrees incline, runners applied 5 percent less force on their legs but reached the top 2.5 percent faster.

Picture from Run247.com

Even Killian Jornet uses trekking poles (pictured above). Why shouldn't you?

There you go, three ways to become a better trail runner. Strength training, varying your pace and trekking poles. Watch out for tree roots on the trails while running!

References

Besson, T, Sabater PF, Varesco G et al (2023). Elite Vs Experienced Male And Female Trail Runners: Comparing Running Economy, Biomechanics, Strength, And Power. J Strength Cond Res 1: 37(7): 1470-1478. DOI: 10.1519/ JSC.0000000000004412

Sabater PF, Besson T, Berthet M et al (2023). Elite Road Vs Train Runners: Comparing Economy, Biomechanics, Strength, And Power. J Strength Cond Res 1: 37(1): 181-186. DOI: 10.1519/ JSC.0000000000004226

Corbi-Santamaria P, Herrero-Molleda A, Garcia-Lopez J et al (2023). Variable Pacing Is Associated With Performance During The OCC Ultra-Trail Du Mont-Blanc (2017-2021_. Int J Environ Res Pub Health. 13: 20(4): 3297. DOI: 10.3390/ijerph20043297

Giovanelli N, Pellegrini B, Bortolan L et al (2023). Do Poles Really "Save The Legs" During Uphill Pole Walking At Different Intensities? Eur J Appl Physiol. DOI: 10.1007/s00421-023--05254

Strength Matters More Than Size

Pawel Poljanski's legs at the Tour De France

My colleague was wondering why I was not 'big' (or muscular) despite exercising regularly. I explained to her I was more Type I muscle dominant (or slow twitch muscle) as most endurance athletes are. Those who have predominantly Type I muscle fibers are lean, not big and muscular.

Her obesrvation is accurate. I actually lift weights twice a week and even though I can squat 90 kg, my thighs are still skinny.

I also explained to her that it is better to be strong than have big muscles. Weight training can make you stronger and your muscles bigger. They are both related since bigger muscles are usually stronger. However, they are not identical. You can get stronger without adding muscle bulk. 

This happens when the signaling from your brain to your muscles become more efficient and how effectively your muscle fibers are recruited. You can add muscle without getting stronger, this typically happens when you gain weight.

Strength is also a much better predictor of cognitive performance than muscle mass. Storoschuk and colleagues (2023) studied 1424 adults above 60 years of age between 1999 and 2002 in a health and nutrition examination study (NHANES). These subjects had DEXA scans to assess body composition, leg strength tests, a digit symbol substitution test (cognitive test) and questionnaires that assessed physical activity habits. The DEXA scan is used to determine how much muscle one has in their arms and legs and fat-free mass index (FFMI), which shows total muscle to height.

The figure above presents the benefits of different variables on cognitive performance. The farther on the right each square is, the greater the cognitive benefits. You can see that low FFMI (low muscle mass) has no significant effect on cognitive scores, while peak leg force (a measure of strength) definitely have a significant benefit. Those who did resistance training (or weight training) for at least once a week has an even stronger effect.

Strength explained about 5 percent of the variance in cognitive scores, while muscle mass explained only 0.5 percent. Low strength levels raised the risk of premature death, but low muscle mass did not. In contrast, another study by Tessier et al (2022) found that low muscle mass predicted more rapid cognitive decline over a 3 year follow up period, after accounting for differences in strength. Perhaps it would be premature to conclude that muscle mass (being big) does not matter.

Confused? Storoschuk et al (2023) explained that there is a difference between the muscle you get from physical activity and muscle you get in the process of gaining weight. Greater muscle mass may just be a larger body size rather than greater strength, which does not seem to translate into protection from cognitive decline and other health benefits.

Moreover the conflicting results from the 2 studies are possible due to different popolulations, different cognitive tests and different sample sizes. 

My take on this? It is good if you have big muscles and I will still lift weights twice a week to at least maintain and avoid losing what I have. Getting stronger is much better, and that is the main reason why I do weight training. Even though I do not seem to gain muscle I am able to increase the reps and quality of the exercises I perform. 

So, to ward off cognitive decline, strength training is just as important as aerobic exercises.

References 

Tessier A, Wing SS, Rahme E et al (2022). Association Of Low Muscle Mass With Cognitive Function During A 3-Year Follow-up Among Adults Aged 65 To 86 Years In The Canadian Longitudinal Study On Aging. JAMA Netw Open. 5(7): e2218826. DOI: 10.1001/jamanetworkopen.2022.19926

Storoschok KL, Gharios R, Potter GDM et al (2023). Strength And Multiple Types Of Physical Activity Predict Cognitive Function Independent Of Low Muscle Mass In NHANES 1999-2002. Lifestyle Med. 4: e90. DOI: 10.1002/lim2.90