Beyond hamstring curls: effective recruitment with hip extension and Nordics

2016 Rio Olympics – Soccer –  Cristiane (BRA) of Brazil reacts after an injury. REUTERS/Gonzalo Fuentes 

Studies looking at muscle activation often rely on surface electromyography (sEMG) readings to determine muscle functionality. New technology, however, enables scientists to get a more accurate picture of muscle contractions. Functional magnetic resonance imaging (fMRI) provides a better measurement of muscle activation by recording the T2 relaxation time of tissue water.

Scientists from Australia used this technology to compare the spatial patterns of hamstring muscle use in women performing two different exercises(1). Six recreationally active women performed the Nordic hamstring exercise and the 45º prone hip extension exercise during different exercise sessions. The researchers encouraged all subjects to execute the exercises maximally. Before the exercise session and after performing five sets of six reps of the assigned exercise, the subjects underwent an fMRI scan of both thighs.

When evaluating the fMRI images, the researchers identified a region of interest that approximated the muscle belly of each hamstring muscle. They were then able to extrapolate the data to indicate the activation of each muscle. The study found that the 45º hip extension exercise recruited the whole hamstring complex, but used the semitendinosus (ST) muscle significantly more than the biceps femoris short head (BFSH). The Nordic hamstring exercise also recruited the ST significantly more than the BFSH.

The difference between the exercises is that the Nordic exercise targets the ST specifically, while the hip extension exercise appears to recruit the whole hamstring complex. The authors state that because the ST is likely more involved in the stability of the knee and plays a role in supporting the ACL, the Nordic exercise may more effectively help an ACL injury prevention program.

Because the 45º hip extension exercise more evenly recruits the hamstring complex, especially the BFLH, it may be a more effective exercise for those who suffer from repeated hamstring strain. The authors theorize that these exercises activate muscles differently based on the kinematics of the muscles. They point out that the ST has a larger moment arm at the knee. Therefore, the movement at the knee joint and stabilization of the hip joint during the Nordic exercise preferentially activates this portion of the muscle. Reciprocally, the hip movement (with a stabilized knee) during the hip extension exercise also engages the biceps femoris, which has a greater moment arm at the hip.

This study was small and unique in that it studied the hamstring function in female subjects only. However, it gives a glimpse into the importance of determining the desired outcomes and understanding the prescribed exercises’ mechanisms. While Nordic exercises may be trendy, women suffering from repeated hamstring strain may benefit from the 45º hip extension exercise.

Reference

1. JOSPT. 2018 Aug;48(8):607