Comparison of plantar loads during treadmill and overground running

Abstract

Objectives

The objective of this study is to compare plantar loads during treadmill running and running on concrete and grass surfaces.

Design

Crossover study design was used in the study.

Methods

A total of 16 experienced heel-to-toe runners participated in the study. Plantar loads data were collected using a Novel Pedar insole sensor system during running on the treadmill, concrete, and grass surfaces at 3.8 m/s running speed and then analyzed.

Results

Compared with running on the two other surfaces, treadmill running showed a lower magnitude of maximum plantar pressure and maximum plantar force for the total foot, maximum plantar pressure at two toe regions, and maximum plantar force for the medial forefoot region and two toe regions (p < 0.0017). Treadmill running also showed a longer absolute contact time at two toe regions compared with running on the other two surfaces (p < 0.0017).

Conclusions

Treadmill running is associated with a lower magnitude of maximum plantar pressure and a lower maximum plantar force at the plantar areas. These results suggest that the plantar load distribution in treadmill running is not the same as the plantar load distribution in running on overground surfaces. Treadmill running may be useful in early rehabilitation programs. Patients with injuries in their lower extremities may benefit from the reduction in plantar loads. However, the translation to overground running needs investigation.

Introduction

Treadmills are widely used in laboratory settings for training and research to control speed and slope easily.¹ The increased use of treadmills in scientific investigations raises issues on differences in running patterns on a treadmill and on overground surfaces. Some studies have found that compared with running on overground surfaces, treadmill running exhibits a shorter flight phase, decreased stride length, and increased cadence at a moderate speed of 3.3–4.8 m/s.² On the other hand, other studies have shown that the some kinematic variables (e.g., hip adduction angle, hip internal/external rotation, ankle eversion, maximal pelvic rotation) of treadmill gait are similar to those of overground gait.3, 4 To date, whether the treadmill-based analysis of running mechanics can simulate overground running mechanics remains a contentious issue.4, 5

Plantar loads are widely used to assess injury risks,⁶ and many studies have discussed plantar pressures when running and performing specific sports movements on different overground surfaces.7, 8, 9, 10, 11 However, little is known about the differences in plantar load distributions during treadmill and overground running. Impact forces on the lower extremity, which are associated with repetitive loading, are responsible for overuse injuries in the lower extremity.12, 13 A higher plantar pressure underneath the medial side of the foot has been found in runners with exercise-related lower-extremity pain,¹⁴ and has been assumed as one risk factor associated with sports injury.¹⁰

The identification of impact forces and plantar pressure distribution characteristics during treadmill and overground running can help reveal risk factors related to sports injury. Common overground surfaces for runners include concrete, asphalt, synthetic rubber sports track, and natural turf. Concrete and asphalt are the most commonly used surfaces for recreational and marathon runs.¹⁰ Natural grass surfaces have been used previously to study plantar loads during running and performing specific sports movements.8, 9, 10 Given the contention about running mechanics between different surfaces, this study compares plantar loads of running on a treadmill, concrete, and grass. We hypothesize that plantar loads during treadmill running are lower than those during overground running.