6-Week Adaptation to Minimalist Running Shoe Sign Boosts Running Economy, Doubles Improvements in 5k Time-Trial

The study subjects were trained runners, results may differ for noobs.

I openly admit that the focus of my SuppVersity articles has rarely been on endurance exercises like running. I am well aware, though, that many of you are participating in 10k and or marathon runs and will thus be interested in the results of a recent study in the Journal of Science and Medicine in Sport - a study that tried to get to the bottom of the ambiguous results on the performance enhancing effects of minimalist shoe wear, which appears to be divided into studies supporting its efficacy and papers reporting downright performance decrements when runners are transitioned from classic to lightweight minimalist shoes.
Even if you're not a passionate runner, you will not be surprised to hear that a 2015 review by Fuller et al. confirms that you can hardly overemphasize the importance of choosing the "right" running shoes, because they can and will affect every runner's maximal performance (Fuller 2015). Back in the day, the scientists from the University of South Australia concluded that...

Table 1: Results of a meta-analysis of the effect of footwear on running performance & economy in distance runners (Fuller 2015).

• running shoes with greater shoe cushioning, greater longitudinal shoe stiffness and greater shoe comfort were associated with improved running economy, while
• running in light shoes or running without shoes = barefoot reduced metabolic cost compared with running in heavy shoes but there was no difference in metabolic cost between running in light shoes and running barefoot

Fuller et al. realized, however, that there were "[n]o studies [that had] investigated the effect of footwear on running performance measured using a time-trial or time-to-exhaustion test" (Fuller 2015). Meanwhile, other studies have suggested that wearing minimalist shoes (or racing flats) during running competition should be advantageous for running performance, as well. In fact, Fuller et al. are right to point out in their latest paper that "runners have been doing this for many years" (Fuller 2017).

Should all these runners be wrong? Mislead by ads and the "cult" of barefoot running?

After all, the encouraging data from a pilot trial, Fuller et al. conducted last year (Fuller 2016),
were not confirmed in subsequent controlled trials which found that

"training in minimalist shoes did not improve running economy when (1) runners followed a flexible minimalist shoe training prescription that allowed them to increase minimalist shoe mileage from week 4-10 as they felt was appropriate or (2) prescribed use of minimalist shoes was combined with instructions to use a forefoot footfall pattern and increase stride rate" (Fuller 2017).

With small sample sizes (n≤25), different instructions being provided to runners and, most importantly, the absence of study with standardized training regimen for both the minimalist and control shoe study, the research has yet eventually not gone beyond the pilot stage, anyway.
Running theory and biomechanics tell us that the way barefoot and minimalist shoe running promote a forefoot running pattern should have significant performance advantages, though. In the short term, i.e. when scientists had habitual rearfoot runners switch to a forefoot pattern in a single-session trial (e.g. Gruber 2013), though, the enforced change from a rearfoot to forefoot footfall pattern resulted in either similar or poorer running economy. No wonder, after all, runners find it difficult to maintain a forefoot footfall pattern throughout a prolonged run due to fatigue of the ankle plantar-flexor muscles (Jewell 2017). It is thus only logical that Fuller et al. assumed that a study design that would allow their subjects to adapt to the novel requirements of a more forefoot-based running as it is enforced in minimalist shoes would make up for habituation and training and thus realize the previously explained (see red box) beneficial effects on both, running economy (has already been proven on the small scale) and time trial performance (hasn't been investigated, at all).

To this ends, Fuller et al. conducted a randomized parallel intervention trial with 61 trained runners who gradually increased the amount of running performed in either minimalist (n = 31) or conventional (n = 30) shoes during a six-week standardized training program.

Figure 1: Participant flow chart (Fuller 2017) | * Participant excluded as an outlier after running 5-km time-trial 114 seconds slower at completion of the six-week training program.

"Eligible participants were 18-40 years old, ran at least 15-km/week, could run 5-km in <23 minutes, used conventional shoes, had no previous minimalist shoe experience and were habitual rearfoot footfall runners. Footfall pattern eligibility was assessed during five over-ground running trials at preferred running speed in the runners own shoes using a high-speed digital camera filming at 200 Hz. Only runners that landed heel first in all trials were eligible. Runners were excluded if they used orthotics, had a current or recent musculoskeletal injury (<3 months) or history of surgery in the previous year" (Fuller 2017)

Training duration and relative intensity were standardized across participants. The training intensity was prescribed relative to peak heart rate (HRPeak) achieved during baseline 5-km time-trial assessment and involved two interval running sessions at 85-90% HRPeak and two continuous running sessions at 65-80% HRPeak each week. The duration of interval training was increased throughout the program so that a greater percentage of training was completed at high intensity (85-90% HRPeak). Participants were instructed not to perform any additional training.

Figure 2: The scientists chose a gradual increase in running time in the newly assigned shoes as "a safe and realistic target for participants to achieve during the 6-week intervention" (Fuller 2017)

Runners in each group gradually increased the amount of running in their allocated shoes and decreased the amount of running in their usual running shoes. Participants completed ~5% of weekly running in their allocated shoes during Week 1 and this increased to ~35% of weekly running in weeks six. The scientists explain this very moderate approach as follows:

"Increasing minimalist shoe use to 35% of weekly running was chosen as a safe and realistic target for participants to achieve during the 6-week intervention. Participants completed a total of 3.5 hours (40-50 km) of running in their allocated shoes during the intervention. Compliance was calculated by dividing the total duration of training performed in allocated shoes (from training diaries) by the total duration of prescribed allocated shoe use" (Fuller 2017).

It is thus possible that the subjects' adaptation process had thus only begun, when they performed the retests, i.e. a 5-km time trial performance, running economy, ankle plantar-flexor strength, footfall pattern, stride rate and length tests - the same tests all subjects had completed at baseline.
Against that background, I find it all-the-more surprising that Fuller et al. observed a small, but significant improvement in time-trial performance (Effect size (ES): 0.24; 95% confidence interval (CI): 0.01, 0.48; p = 0.046) and a medium, likewise significant improvement on running economy (ES 0.48; 95%CI: 0.22, 0.74; p < 0.001) in the minimalist vs. conventional shoe group.

Figure 3: Training effect (left) as change (*for time-trial and the running economy those would be negative values, but I thought it's easier to read if I reverse that) and effect size for the pre-/post-comparison in the two groups (Fuller 2017).

What the scientists didn't observe, however, were effects on stride rate (ES: 0.04; 95%CI: −0.08, 0.16; p = 0.53) or length (ES: 0.06; 95%CI: −0.06, 0.18; p = 0.35). ankle plantar-flexor concentric (ES: 0.11; 95%CI: −0.18, 0.41; p = 0.45), isometric (ES: 0.23; 95%CI: ‐0.17, 0.64; p = 0.25), or eccentric strength (ES: 0.24; 95%CI: ‐0.17, 0.65; p = 0.24); and even though the minimalist shoes caused large reductions in the ratio of rear-to-forefoot balance, (ES: 1.03; 95%CI: 0.65, 1.40; p < 0.001), only two runners changed to a forefoot footfall.
References:

• Esculier, Jean-Francois, et al. "A consensus definition and rating scale for minimalist shoes." Journal of foot and ankle research 8.1 (2015): 42.
• Fuller, Joel T., et al. "The effect of footwear on running performance and running economy in distance runners." Sports Medicine 45.3 (2015): 411-422.
• Fuller, Joel T., et al. "Effects of a minimalist shoe on running economy and 5-km running performance." Journal of Sports Sciences 34.18 (2016): 1740-1745.
• Fuller, Joel T., et al. "Six-week transition to minimalist shoes improves running economy and time-trial performance." Journal of Science and Medicine in Sport - Available online 21 April 2017
• Gruber, Allison H., et al. "Economy and rate of carbohydrate oxidation during running with rearfoot and forefoot strike patterns." Journal of Applied Physiology 115.2 (2013): 194-201.
• Jewell, Carl, Katherine A. Boyer, and Joseph Hamill. "Do footfall patterns in forefoot runners change over an exhaustive run?." Journal of sports sciences 35.1 (2017): 74-80.