Research: Injury Rates in Runners Wearing Traditional vs Minimal Footwear

Better late than never!  Thank you for your patience as we have been working through the ins and outs of conducting our first pilot study as well as publishing our first research paper over the past (very long) while.  We hope you enjoy reading about the study and our findings. Thank you to everyone who volunteered their time and resources to help us make this project happen.  From the practicioners doing the before and after testing to the volunteer subjects for joining the study.  Thank you so much.  Enjoy!

Sarah and Kim

A comparison of incidence of injury between runners wearing traditional versus minimal footwear during an introductory run:walk program.

Kim Senechal

Sarah Seads

Abstract

The purpose of this pilot study was to compare the incidence of injury between runners wearing traditional versus minimal footwear during an introductory run:walk program. Twenty-seven subjects were divided into three running groups: beginner minimal (BM), beginner traditional (BT) and experienced minimal (EM). We recorded the incidence of injury as reported by subjects during the course of a ten week progressive run:walk program. The subjects were required to report any pain experienced and to include the location, severity, duration and self-treatment. Pain was categorized as a either a symptom or an injury. A symptom was defined as ‘any physical discomfort experienced during a run.’ An injury was defined as ‘any symptom experienced that was significant enough to require the cessation of all running for seven or more days.’ Of the runners studied, 13 subjects reported 23 symptoms, and 5 subjects had to stop running due to injury. The subjects in the EM group had the highest incidence of injury (28.6%). The lowest incidence of reported injury was found in beginner runners in minimal footwear. However there was no meaningful difference in incidence of reported symptoms between groups. A descriptive statistics model showed a high correlation (0.52) between age and injury. However, low correlations were found between incidence of injury or reported symptoms, and gender, weight, experience and type of footwear. This study had several limitations (small sample size, high attrition rate, lack of randomization between groups) which preclude making statistical conclusions. However, this study does suggest that runners who begin running in minimal footwear from the start of their training may have a lower risk of injury than both beginner runners wearing traditional footwear and experienced runners transitioning to minimal footwear from traditional footwear. Further research is needed further explore the findings of this study, as well as other variables that may contribute to running injury.

Introduction

Running has been an integral part of human movement for as long as we have lived on earth. The modern running shoe was invented in the 1970s^i. Yet prior to this, runners were either barefoot or wore minimal footwear that served mainly to protect the foot from environmental hazards such as ice, sharp rocks, or hot sand. We are born barefoot, yet in many parts of the world children are frequently shod in a variety of footwear before they can even walk. These individuals subsequently progress through life with their feet growing and developing but becoming very dependent on supportive shoes that provide a barrier between their bodies and the ground. Changes in how we walk and run have inevitably resulted, and this has been accompanied by debate as to whether these changes have truly been progressiveⁱⁱ. In light of this there has been a trend to move back to a more natural style of running, either barefoot or in minimal footwear.

The invention of the modern running shoe or traditional shoe (TS) brought with it claims of reduced injury ratesⁱⁱⁱ and increased athletic performance through cushioning, arch support and an elevated heel. With the introduction and resultant popularity of such shoes, alterations were noted in running gait and kinematics. For example, endurance runners began to land with their heel first rather than a more natural mid-foot or forefoot strike pattern.¹ The TS design allows rear foot or heel strike running to comfortably occur as a result of thick cushioning in the heel of the shoe. Running shoe manufacturers promote the cushioning, rigid structure and motion control components of the TS's as a way of decreasing running injuries.

It has been demonstrated that barefoot or minimal footwear (MF) naturally land with a forefoot or mid-foot strike pattern.¹ Recent research has shown that this landing pattern results in reduced ground reaction forces and therefore less impact on the body.¹ There are many proposed benefits of MF running including increased strength in the foot muscles and therefore decreased pronation, decreased energy expenditure, increased proprioception, and increased comfort.^iv

However, with a growing number of runners switching from TS to MF, some concerns have arisen within the medical and running communities regarding injury rates. Anecdotal and case study evidence suggests that MF runners are at increased risk for Achilles tendinitis, calf strain and metatarsal stress fracture - (particularly of the second metatarsal).^4,v While there is little evidence that moving to an increasingly supportive shoe in the 1970s reduced injury rates in runners, there are also very few studies that have investigated the incidence of injury between runners who wear a TS versus MF on a modern running surfaces such as asphalt.

The purpose of this study was to compare the incidence of injury between runners wearing a TS versus MF during a 10 week introductory running program.

Methods

Data were collected from 6 male and 21 female volunteers between the ages of 22 and 65. All of the subjects completed a 10-week progressive run-walk program wearing either a TS or MF. Each week the subjects were required to complete a minimum of three training runs including one weekly group run.

Subjects were divided into three categories based on their reported running experience and their footwear selection: Beginner Minimal (BM), Beginner Traditional (BT) and Experienced Minimal (EM). Running experience was determined through a pre-assessment questionnaire and subjects chose their footwear group by self-selection.

Minimal footwear was defined as having a difference in stack height of 4mm or less between heel and forefoot, as well as no more than 15mm of cushioning in any part of the sole between the foot and ground. Traditional footwear was defined as having a difference in stack height of greater than 4 mm between heel and forefoot, as well as greater than 15mm of cushioning in any part of the sole between the foot and ground.

Footwear measurements were collected by the Running Warehouse.

Stack height was measured from the bottom of the outsole, where the shoe sits on the ground, to the top of the last (directly underneath the insole/sock liner). A depth caliper, which was attached to a chemistry stand using a 90 degree adapter, was used to attain the stack height measurements. The chemistry stand provided a solid support, and the depth gauge could be set to any height. For every shoe, averages of three depth gauge measurements were taken in both the heel and the forefoot.

Running experience was based on self-assessment. Beginner runners reported having no prior running experience or no running for the last 4 months. Experienced runners reported the ability to currently run a minimum of 20 minutes, 3 days per week, but had never run in minimal footwear. All runners in both experience level groups confirmed that they had no running-induced injuries for a minimum of 6 weeks before the start of the study.

The run:walk program was based on a gradual learn to run format. The program began with one minute of light running followed by two minutes of walking and was repeated over six intervals. Each week after the second week the time spent running increased while the walking interval stayed at one minute. The final week of the program required the subjects to run continuously for 20 minutes. Each run:walk session began and ended with 5 minutes of walking and the session concluded with a series of general running stretches. Stretches were included for the quadricep, hamstring, hip flexor, gastrocnemius and soleus muscle groups. Stretches were held for 30 seconds each.

Each week, the subjects were required to complete the run:walk program under the supervision of study researchers, and 2-3 additional times on their own. The additional runs were of the same interval duration as the weekly supervised sessions, and subjects were required to report these to ensure that they had adhered to the required number of sessions. The subjects completed all of their runs on a flat asphalt surface while wearing the same footwear chosen at the beginning of the study. It was mandatory.

The subjects were required to report any pain experienced and to include the location, severity, duration and self-treatment. Pain was distinguished as a symptom or an injury. A symptom was defined as ‘any physical discomfort experienced during a run.’ An injury was defined as ‘any symptom experienced that was significant enough to require the cessation of all running for seven or more days.’

These data were analysed using descriptive statistics and correlation to determine if there was a difference in the incidence of injury or occurrence of symptoms among the footwear groups or related to physical characteristics or experience of the subjects during the 10-week running program.

Results

The study began with 27 subjects. The collective physical characteristics of subjects in the three groups are presented in Table 1. There were no meaningful differences in age, height or weight among the groups. Moreover, the male to female ratio was similar between the groups.

Table 1: The collective physical characteristics of subjects in the three groups. Values are means ± SD.

Physical Characteristics

Beginner Traditional (n=11)

Beginner Minimal (n=9)

Experienced Minimal (n=7)

Age (years)

36.9 ± 10.5

36.9 ± 10.5

39.7 ± 12.0

Height (cm)

166.2 ± 7.2

167.9 ± 10.3

166.3 ± 6.8

Weight (kg)

81.9 ± 15.3

75.4 ± 13.6

72.7 ± 14.6

Males (%)

18.2

33.3

14.3

Females (%)

81.8

66.7

85.7

During the course of the study, five subjects stopped running due to injury (Table 2). The EM group had the highest incidence of injury as a percentage of the total but this was not meaningfully significant as compared to the other groups. Of the five injuries that were reported during the study, three were in the calf region, one was in the knee and one was in the foot. There were 23 occurrences of symptoms reported among the three groups during the course of the study (Table 3). There were no significant differences in incidence of reported symptoms among the three groups. The symptoms reported varied in location over 9 anatomical regions. The occurrence of these symptoms by region is presented in Table 4.

When additional factors including the subjects' physical characteristics were examined, there was a high correlation (r=0.52) between age and injury. There were very low correlations between the incidence of injury or the occurrence of symptoms, and gender, weight, experience and type of footwear.

Table 2: The number (incidence) and proportion of subjects who reported injuries within the three groups

Group

Number reporting injury

Percentage of group

Beginner Traditional

2

18.2

Beginner Minimal

1

11.1

Experienced Minimal

2

28.6

Total

5

18.50%

Table 3: The number (incidence) and proportion of subjects who reported symptoms within the three groups

Group

Number of subjects reporting symptoms

Percentage of group

Beginner Traditional

8

34.8

Beginner Minimal

7

30.4

Experienced Minimal

8

34.8

Table 4: Occurrence of symptoms by anatomical region within the three groups

Anatomical region

Symptoms

Group

Number

Percentage

Beginner Traditional

Beginner Minimal

Experienced Minimal

Calf

6

26.1

3

3

Foot

4

17.4

2

1

1

Shin

4

17.4

3

1

0

Heel

2

8.7

1

0

1

Knee

2

8.7

1

0

1

Hip

2

8.7

0

2

0

Achilles

1

4.3

0

0

1

Thigh

1

4.3

0

0

1

Ankle

1

4.3

1

0

0

TOTAL

23

100

8

7

8

Discussion

When we examined the reports of injury between runners wearing a traditional running shoe versus minimal footwear during a 10 week introductory running program we found that experienced runners running in minimal shoes for the first time had a higher incidence of injury than beginner runners in traditional shoes. The lowest incidence of reported injury was found in beginner runners in minimal footwear. Experienced runners who switch to minimal footwear may have a higher chance of getting injured due to a tendency to run faster or further. In this study, while all participants self-reported that they completed their weekly unsupervised runs, the experienced group actually ran more by combining their regular running in TS to the study runs in MF. Experienced runners in TS may have established motor pathways that determine running gait patterns. This could mean that they may be less likely to adapt to MF that allows the foot to function very differently (ie. Heel drop and less rigidity). In contrast, a beginner runner would not likely have a predetermined running gait nor strong motor programming and may adapt more easily to MF. Beginner runners also tend to run more slowly. We recommend that experienced runners who are considering switching to minimal shoes allow their body to adapt to the new footwear over a gradual period of time (ie longer than 10-weeks). Based on the results of this study, beginner runners who choose minimal footwear may reduce their chance of injury as compared to those who choose traditional shoes, provided they follow a gradual run:walk program.

Of note, calf injuries were only reported from the two MF groups and not from the TS group. As a population, North Americans typically wear shoes from an early age and likely adapt to the support of footwear that frequently includes elevated heels of variable heights as well as arch support and rigidity. Running in MF may place additional stress on the calf musculature of populations that have adapted to TS, for both running and daily living, over the course of their lives.

It is notable that there was a strong correlation between age and injury. However, there was a very low correlation between footwear type or running experience, and incidence of injury overall.

Limitations

Firstly, there was a lack of random assignment to groups. Since random assignment is considered the strongest way to account for the many variables that may lead to differences in results among groups, without it we can only conjecture on possible reasons for these differences.

Secondly, the study was comprised of a small sample size. A large sample size is more representative of the population, limiting the influence of outliers or extreme observations. A sufficiently large sample size is also necessary to produce results among variables that are significantly different.

Finally, this study did not include a control group for the Experienced runners. With no Experienced Traditional group, it is unknown how the incidence of injury rates would have compared with the Experienced Minimal runners.

Conclusion

Statistically significant conclusions were not made due to the limitations of this study. However, interesting trends were of note and can be used to generate discussion.  Based on the results of this study, beginner runners who choose minimal footwear may reduce their chance of injury as compared to those who choose traditional shoes, provided they follow a gradual run:walk program. Experienced runners who ran in minimal shoes for the first time had the highest incidence of injury and caution is advised when transitioning to minimal footwear.  Further research is needed to explore other variables that may contribute to incidence of injury such as biometric measurements including calf length and strength, arch height, and great toe extension, foot strike patterns, running speed and psychosocial factors.

i

Lieberman, D.E. et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 08723, 1-5 (2010)

ii Warburton, M. Barefoot running. Sportscience. Sportsci.org. http://www.sportsci.org/jour/0103/mw.htm

iii Schwellnus, M.P., Stubbs, G. Does running shoe prescription alter the risk of developing a running injury? International SportMed Journal. Vol.7 No. 2. 138-153 (2006).

iv Barefoot Training Tips. http://barefootrunning.fas.harvard.edu/5BarefootRunning&TrainingTips.html

v Giuliani, J. Masini, B. Alitz, C. Owens, BD. Barefoot-simulating footwear associated with metatarsal stress injury in 2 runners. Orthopedics. Vol. 34 No. 7 e320-323. (2011)