Background Treadmills are often used in research, clinical practice, and training. Biomechanical investigations comparing treadmill and overground running report inconsistent findings. Objective This study aimed at comparing biomechanical outcomes between motorized treadmill and overground running. Methods Four databases were searched until June 2019. Crossover design studies comparing lower limb biomechanics during non-inclined, non-cushioned, quasi-constant-velocity motorized treadmill running with overground running in healthy humans (18-65 years) and written in English were included. Meta-analyses and meta-regressions were performed where possible. Results 33 studies (n = 494 participants) were included. Most outcomes did not differ between running conditions. However, during treadmill running, sagittal foot-ground angle at footstrike (mean difference (MD) − 9.8° [95% confidence interval: − 13.1 to − 6.6]; low GRADE evidence), knee flexion range of motion from footstrike to peak during stance (MD 6.3° [4.5 to 8.2]; low), vertical displacement center of mass/pelvis (MD − 1.5 cm [− 2.7 to − 0.8]; low), and peak propulsive force (MD − 0.04 body weights [− 0.06 to − 0.02]; very low) were lower, while contact time (MD 5.0 ms [0.5 to 9.5]; low), knee flexion at footstrike (MD − 2.3° [− 3.6 to − 1.1]; low), and ankle sagittal plane internal joint moment (MD − 0.4 Nm/kg [− 0.7 to − 0.2]; low) were longer/higher, when pooled across overground surfaces. Conflicting findings were reported for amplitude of muscle activity. Conclusions Spatiotemporal, kinematic, kinetic, muscle activity, and muscle-tendon outcome measures are largely comparable between motorized treadmill and overground running. Considerations should, however, particularly be given to sagittal plane kinematic differences at footstrike when extrapolating treadmill running biomechanics to overground running. Protocol registration CRD42018083906 (PROSPERO International Prospective Register of Systematic Reviews).

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We would like to thank Dewolf et al. [1] for their interest in our review [2] and for providing additional insights into the effects of belt-speed fluctuations on treadmill running biomechanics. We believe that their commentary offers an interesting explanation for some of the biomechanical differences observed between treadmill and overground running. As also stated in our conclusion, we, therefore, agree with Dewolf et al.[1] that researchers, clinicians and athletes should assess belt-speed fluctuations and take their effects on running biomechanics into consideration. Compliance with Ethical StandardsConflict of interest Joel T. Fuller and Jonathan D. Buckley have been authors on some research projects that have evaluated the effects of different running shoes on running performance, biomechanics and physiology; those projects involved the use of running shoes that were donated by the shoe industry, either from running shoe retail stores or ASICS Oceania. Chris Bishop has received funding from both ASICS Oceania and Brittain Wynyard for professional services related to footwear. Guillaume Rao has received funding from Decathlon for professional services related to footwear to evaluate the effects of different running shoes on running performance, biomechanics and physiology. No companies played any role in the design, conduct or interpretation of the present research. The remaining authors declare no conflicts of interest.