Is Running on a Treadmill Effective?

When the weather turns cold, many people turn to the treadmill for their run training. Obviously there are differences between the treadmill and the road. The two biggest differences are the more buoyant landing from the treadmill and slight "feedback" from this, and of course the moving track, which eliminates much of the need to pull the leg through being it does it for you. Do these differences have an effect on training effectiveness? Do they set you up for injury? Do they result in muscle weakness or long term biomechanical changes? In other words, is running on a treadmill harmful to your training, or is it a good alternative to running outside in the cold?

Below are common biomechanical "adaptations" we make to running on a treadmill:

Joint Function

• Shorter stride
• Increased cadence
• Foot landing moves closer to being directly underneath our bodies, and typically more toward midfoot
• Shorter stride time
• Greater knee angle
• Reduced ankle angle
• Increased hip extension at toe off
• Reduced "braking"
• Reduced knee joint forces
• Reduced peak ground reaction force
• Greater ankle joint forces

Muscle Function

• Reduced oxygen consumption (aka less energy required at the same speed) on treadmill
• Increased force on muscles and changes in muscle dominance during certain stride phases

The Big Picture

Although there are statistically significant biomechanical differences between running on a treadmill and running outdoors, these adaptations are really quite subtle, and I couldn't find any reliable data in my research review suggesting that you are setting yourself up for future injury and/or permanent alterations in running form. However, the key conclusion statement is that running outside and running on a treadmill are very similar, but not the same. If your goal is simply to maintain some level of fitness and you are absolutely opposed to running outside in the cold, a treadmill is a good solution. However, because of the increased joint forces, muscle forces, and energy required to run outside, especially on varied terrain, it is my opinion (and that of many others) that you should take a step back in distance/time and speed when you begin running outside to 60% of you max distance/time on the treadmill. Then, work your way up, increasing distance/time by 20% per week until you reach the distances you were doing on the treadmill. 

Regarding performance, a treadmill can provide neurological feedback that can increase top end speed. This effect looks to be lost when a person is only running on a treadmill for training because of the increased resistance when you switch to running outside. However, coaches and research (albeit, small scale research) will tell you that using a treadmill periodically for your speed workouts is an excellent way to improve top end speed.