Muscular and neuromuscular training are a huge focus in sport in an effort to improve performance and prevent injury in athletes. Despite lots of research on the musculoskeletal system, most training programs only focus on muscular strength and power while ignoring bone strength. Optimizing bone strength in athletes may prevent stress fracture, a common overuse injury. The goal is to improve bone strength in order to sustain loading during both practice and performance without injury.
Bone’s adapt to the loading from their sport however, a large percentage of athletes develop stress fractures accounting for up to 20% of all sports medicine clinic injuries; an indication of relatively weak bones in some athletes (Fredericson et al. 2006). A recent article reported that stress fracture injury rates in collegiate athletes range from 8.29% in men’s basketball to 28.59% in women’s cross country (Rizzone et al. 2017). Sport is good for bones, the consistent and focused training of athletes provide the much needed loading on the skeletal system. Both higher bone density and larger bone size has been reported in athletes compared to their non-athletic counterparts (Greene et al. 2012; Haapasalo et al. 2000). Racquet sport athletes provide a unique model to investigate the benefits of loading on bone. Athletes’ playing (racquet) arm sustains high loading with each strike of the ball while the contralateral non-playing arm remains unloaded providing a perfect control. Studies have reported a 22% stronger bone on average in the playing arm compared to the non-playing arm (Haapasalo et al. 2000; Kontulainen et al. 2003). High magnitude loading is necessary for skeletal health.
The common phrase “use it or lose it” does not apply to bones. Research has highlighted positive changes to bone strength that seem to last a lifetime especially if training starts at a young age. Work by Warden et al. (Warden et al. 2014) reported long term bone strength changes using baseball players as a model. Baseball players throw using one arm primarily and Major League Baseball (MLB) boasts an alumni association including players who have retired up to 50 years ago. The active and retired baseball players provide the perfect dataset to illustrate both the short-term and long-term benefits of loading on bone. The throwing arm of baseball players was on average 30% stronger compared to their non-throwing arm (Warden et al. 2014). In addition, Warden and colleagues reported a 15.2% greater strength in the throwing arm of a 94 year old retired player (Warden and Roosa 2014). Focusing on the skeletal system during training provides an opportunity for coaches to contribute to their athletes' bone health for a lifetime.
Exercise prescription for bone health
Researchers have spent the last three decades focusing on the specific factors resulting in bone strength optimization. The skeletal system is a very efficient tissue and the training parameters that positively affect bone are different from that of the muscular or cardiovascular systems. Bones benefit from training programs that include unique, variable and high magnitude loading with lots of rest between sessions. Lets review the key factors to consider when developing skeletal-specific training programs.
1. The Higher the Better (Weight Bearing & High Load Exercises)
Weight bearing activities are those when your legs or arms support the weight of your body; for example, running and jumping are weight bearing since they involve a force applied to the ground using your feet and lower limbs. A cartwheel is also weightbearing since your hands and upper limbs apply a force to the ground. Non weight bearing activities are those that use equipment that supports some of your weight, similar to assistive devices such as crutches that decrease the amount of weight you are applying to the ground. Bicycling, rowing and swimming are other examples of non-weight bearing exercises. Weight bearing exercises result in larger loads on your bones. Bones like a challenge, the higher the loading magnitude the better. In addition, exercises that load bones quickly are more beneficial for building bone strength. For example, a jump squat is a better ‘bone exercise’ compared to a bodyweight squat. They are both weight bearing exercises, but the jump squat increases both the magnitude and the rate of loading on the skeleton.
