Many studies have been conducted which have attempted to compare any differences between running outside / overground (OG) and that on a motorised treadmill (TM). The use of TM running at home and at the gym offer convenience and safety – especially when running barefooted in the dark, where it is easy to slip or put your foot into a hole in the ground, or tread in something soft and brown left by a dog or an other animal.
A (basic) review of current literature and website blogs reveal only minimal, if any differences between the two types of running.
TM running produced less hip flexion, according to Sinclair et al, however Wank (1998), found a marked increase in forward lean of the trunk. Both authors and others found runners decrease their step length and an increase in their subject’s cadence on the TM. Kerrigan at al. also agree, stating ground reaction forces at propulsion and mid stance are reduced in TM running. This is probably due to the springiness of the treadmill.
These authors noted that knee abduction and knee joint moments were all reduced in TM compared to OG. It was also noted that the foot struck the ground with a lower angle to the ground. OG running produced more overall range of motion, especially with the trailing leg being more extended prior to toe off.
Most authors now concur that a short strides length, and increased cadence with the foot striking the ground under the Centre of Mass (your trunk) to be an ideal form which reduces the risk of injury, and may enhance performance and speed.
The foot; according to Barton (2015) there is an increase in navicular motion for both walkers and runners, on the TM. This motion is associated with excess foot pronation and several studies, Nigg (1995), Riley (2008) and Sinclair (2013) found that this is increased for TM running. They noted that the navicular bone will tend to move medially and downward during pronation. Greater magnitude and velocity of navicular motion is likely the result of greater vertical ground reaction forces occurring during running Dugan (2005) and Nilsson (1989). This navicular motion is a direct correlation to foot pronation. This is associated with an increase in peak ankle dorsiflexion and foot eversion.
Most current evidence suggests that there is no significant difference in EMG activity of the leg muscles in TM and OG running.
Some runners and forums suggest that treadmill running is slightly easier than OG running possibly due to no wind resistance and some effect of the treadmill belt pulling the foot away. They suggest a small inclination of 1% makes TM running equivalent to OG in running economy terms, Padulo (2012). Although at speeds of less than 7.5mph there was no significant difference in running economy between the two forms.
Chambon et al. (2014) examined the differences in loading on the TM and OG for running shoes of different thickness between the toe area and the heel – known as the drop. They found that loading rates for the minimal shoes and high drop shoes were opposite for the 2 surfaces. They claim loading rates were highest for the low drop/minimal shoes for the OG runners but this was opposite for their TM runners, in that the maximal drop shoe caused higher loading on the TM. They saw that running on the TM caused greater knee flexion and ankle plantarflexion at initial contact for the shod runners, which may be responsible for this loading increase.
In 2013 Hanley et al. found their subjects running on a TM for a distance of 10km altered their gait during the latter half of the run. Continuously, contact time decreased and more time was spent airborne. The authors considered this technique evolved to allow the TM belt to pass under them, and this technique could not be employed for OG running.
To summarise, the TM seems to create what are now considered to be running technique improvements such as shorter stride length, and increased cadence, and a lower angled foot strike. Although many authorities continue to, and probably always will, argue about the ideal position for the foot to strike the ground. It should be stated that the vast majority of runners strike the surface with the heels first (approximately 80%), and running style is very much a personal preference.
The forward lean of the trunk is a negative change in TM running as is the propensity for increased foot pronation. However, these may only be artefacts seen in these studies. Kerrigan (2014) firmly considers that there are no significant differences, and Wank (1998) et al found that the EMG patterns of the leg muscles were generally similar between OG, and TM modes.
Overstriding may be an issue with the TM; for OG running if one tires then running pace will slow and cadence and stride length will be reduced. However, for the TM once fatigue occurs but runners maintain the same pace / speed then it is possible that the stride length will increase as compensation. Using the TM for interval work using the incline will encourage a shorter stride length.
Excess pronators may be advised to limit the amount of TM running, however, the TM may be used to enhance technique and the use of the inclination and speed changes may be useful for interval training sessions. Furthermore, running in cold weather will increase the risk for muscle pulls and strains.
Running shoes with a big drop may cause an increase in loading on the TM – which will affect shoe choice if this is to be avoided, especially in runners returning from injury.
Whatever footwear you choose, be it indoors or outdoors – enjoying your running!