A recent study published in the Journal of Strength and Conditioning Research has found that the distance a dancer can travel with a single leg hop predicts their risk of lower extremity injury.
The researchers recorded horizontal single leg hop distance (measured as a % of the dancer's height), and vertical jump power (measured in watts) in a group of 43 college-age dancers. The dancers were then followed-up for 16 weeks, and their total number of injuries and hours spent dancing were recorded. On average, dancers picked up 3.7 injuries per 1000 hours of dance.
The study found that dancers who were able to travel more than 78.2% of their own height in a single hop were significantly less likely to pick up a lower extremity injury than those who were able to travel less than 78.2% of their own height. Vertical jump power was unrelated to the likelihood of picking up a lower extremity injury.
The authors recommend strength and conditioning coaches use the single leg hop test to identify dancers who may be at higher risk of incurring a lower extremity injury, and include horizontal directional exercises in these dancers' training programmes.
Without access to the full paper, I cannot see whether the authors discuss the mechanisms by which single leg horizontal directional training might protect against injury. My guess is that it would be from strengthening the deep stabilisers of the hip and pelvis; in contrast to vertical jumps, single leg traveling hops require the dancer to absorb a combination of both vertical and directional forces through a single side of the pelvis. It is therefore likely that the horizontal single leg hop is a marker of strong pelvic stabilisers, which will protect the dancer against injury by promoting good alignment and weight placement through the leg and foot.
Ambegaonkar JP, et al. J Strength Cond Res. 2018;E Pub Ahead of Print