‍Purpose: To compare the activation in the hamstrings in the Nordic hamstring curl and flywheel leg curl in soccer players. 

Methods:  

15 amateur soccer players participated in this study.  Each athlete performed 5 reps of each exercise (Nordic hamstring curl and unilateral flywheel leg curl).  The Nordic hamstring curl was performed utilizing body weight and athletes were allowed to use their arms if it was necessary to maintain proper execution of the exercise.  The flywheel group utilized an inertial load power profile to determine which inertial load yielded the highest power output for each individual (optimal power load).  This load was then utilized through the testing trials.  Surface EMG were placed on three different parts (distal, middle and proximal) of the semitendinosus and biceps femoris to measure hamstring activation during the 5 rep trials. Analyzation was performed on the entire eccentric and concentric movements, as well as the upper and lower phases of the eccentric and concentric movements (short vs long muscle lengths, respectively). 

Results: 

In the lower phase of the eccentric movement, both exercises showed similar activation in the hamstring.  In the lower phase of the concentric movement, the flywheel led to higher activation in all three parts of both the bicep femoris (31 – 52%) and the semitendinosus (20 – 35%) in comparison to the Nordic.   

In the upper phase of the eccentric movement, the flywheel led to significantly greater activation in all parts of the biceps femoris (10 – 21%).  Similarly, in the upper phase of the concentric movement the flywheel led to higher activation at each measurement for both muscles in comparison to the Nordic (52 – 79%). 

When analyzing the entire eccentric movement, the only difference was in the proximal part of the semitendinosus for the Nordic (23%).  However, in the concentric phase the flywheel group had higher activation for all three parts of both the semitendinosus (52-68%) and biceps femoris (64 – 78%) in comparison to the Nordic.  

Key Takeaways: 

• At long muscle lengths both Nordic and flywheel leg curls can yield similar muscle activation during the eccentric phases.  However, at short muscle length the flywheel leg curl can have higher activation in the biceps femoris during the eccentric phase. 

• During the concentric phase, the flywheel group has higher activation throughout the entire muscle of both the semitendinosus and biceps femoris in comparison to the Nordic regardless of muscle length (short muscle length, long muscle length, and entire concentric phase)  

•  All together the flywheel leg curls seems to be a feasible and potentially superior alternative to the Nordic hamstring curl, especially during the return to play process.  In addition, it can be substituted for the Nordic hamstring curls during normal training for weaker/heavier athletes.