Running is, in essence, a balanced cyclical activity – in an ideal world, what the right side of the runner's body does during a single step, the left side of the body will mimic in the next step. However, all runners will be imperfectly balanced to some extent just due to natural variation in physical and physiological parameters and it is likely that some of these imbalances will have an effect on performance or injury risk.
Substantial left-right imbalances in strength, range of motion or running biomechanics are known to inhibit performance (by increasing the metabolic cost of running) and are believed to increase injury risk. Imbalances are regarded as being due to a deficiency or compensatory action on one side of the body and if allowed to continue unchecked might lead to atypical loading patterns and the emergence of pain/injury over time. In many applied contexts, conditioners and therapists will aim to rectify imbalances between the left and right of 5% or greater.
Imbalances can be identified in the clinic or gym by completing single-sided exercises or movements to identify left versus right differences. The Balance section of Running Health in NURVV Run makes these measurements more functional by taking them out into the “field” by measuring the left-right balance of the primary underlying running metrics of cadence, step length, footstrike, and pronation.
The overall “Balance” score provides an indication of how well-balanced the runner is across these metrics and the individual metrics can also be inspected individually to identify the source of imbalances. ”Balance” metrics can be analyzed over time to allow the runner to spot the emergence of imbalances and attend to these, particularly if imbalances emerge in combination with a high training load.
Running is a single-leg activity – only one foot is ever in contact with the ground and one side of the body is absorbing the ground impacts – so it is important for the runner to ensure that both lower limbs have the capacity to handle the requirements of the movement. Therefore, it makes a lot of sense for runners to spend a considerable amount of time conditioning the body using single-leg activities. These exercises can have a strength and conditioning (see Performance Factors/Improving Step Length to Run Faster), foot mobility (Running Health/Improving Pronation to Reduce Injury) or a running drills focus (Performance Factors/Improving Cadence to Run Faster).