Preventing Strength Imbalance Orchard et al. (1997) examined hamstring injuries in professional Australian Rules Football players and found that there was significant correlation between the occurrence of hamstring injury and two forms of strength imbalance. Injury was primarily encountered in the hamstring muscles on the player’s weaker leg and hamstring injury was significantly more likely in players with a lower hamstring to quadriceps muscle ratio. This finding was supported by Sugiura et al. (2008), who examined hamstring injuries in elite sprinters and noted that sprains always occurred on the athlete’s weaker side. The authors concluded that deficits in hamstring strength was associated with weakness during the eccentric action of sprinting and resulted in an increased likelihood of injury (Figure 3.1). The implications of these studies is that coaches are able to assist injury prevention by ensuring strength is developed on both sides of the body, using an appropriate balance of unilateral and bilateral exercises. The coach should also ensure that athletes are including an appropriate quantity of
It’s important to note that any well rounded strength and conditioning program should include both unilateral and bilateral movements. Anyone who claims that unilateral movements make you weak, or that bilateral movements are unnecessary, is missing the point. Both bilateral and unilateral exercises are associated with different applications and training adaptations, so don’t neglect one for the other Strength & Conditioning Coach, Giulio Palau
hamstring-specific exercises such as Nordic Hamstring Curls and Deadlifts, to prevent imbalance between hamstrings and quadriceps strength. However, not all evidence supports the view that strength Worrell et al. (1991) found that neither bilateral strength asymmetry nor the ratio of strength between hamstrings to quadriceps had a significant relationship with the occurrence of hamstring injury and Brockett, Morgan & Proske (2004) supported this finding in a study of athletes with a history of hamstring injury. Early clinical evidence also challenges the cause and effect relationship between strength imbalance and hamstring
Ratio (%) of Strength of Quadriceps : Hamstrings
imbalance is a risk factor or cause of hamstring strains.
75 50 25
strains. A single-case study of an elite football player with minimal bilateral asymmetry developed significant asymmetry in hamstring strength 5 days prior to suffering a hamstring strain (Schache et al., 2010). This may suggest that strength imbalance is a symptom rather than a cause of hamstring strains and more research may be required to better understand the relationship between the two. Overall, it is unclear whether strength imbalance is a significant contributor to hamstring strains, but ensuring a sprinter develops strength in their hamstrings and on both sides of their body is still important for achieving athletic success and should still be a priority for the coach.
Injured Athletes F I G U R E 3 .1
From Suguiraet al. (2008), showing athletes who suffered a hamstring injury had significantly greater strength imbalance between hamstring and quadriceps and greater imbalance between limbs