Introduction:
With their potential positive outcomes, hamstring eccentric exercises are becoming increasingly popular within training regimes, with Nordic Hamstring Exercise (NHE) being the most common. NHE is said to be a focused eccentric-type exercise and successful within training programmes to improve eccentric strength and muscle activation. The way an athlete focuses their attention when undertaking such strength-based activities, has the potential to influence strength-based developments. Where attentional focus has been referred to the process in which athletes allocate mental resources to cues, stimuli or states, it has been suggested that an external focus of attention has been beneficial in terms of movement economy. However, it has yet to be shown whether attentional focus influences muscle activation when techniques such as NHE are performed. Furthermore, the aim of the study was to compare the acute effects of attentional focus has on muscle activation and joint knee angle during a Nordic hamstring exercise.
Method: Twelve physically active recreation football players (age 25 ± 3 years) performed a 3 sets of Nordic hamstring exercises whilst undergoing 3 different attentional focus conditions, (External Muscle Contraction, External Upright Posture and Control). Measures of the Bicep Femoris and Semitendinosus were measured for peak EMG (EMGpk) and optimal knee angle (2D Video analysis) were untaken. After each condition participants were asked three specific questions designed to assess use of the respective attentional foci during task execution. Data analysis utilised SPSS (IBM, SPSS). All descriptive statistics were calculated and presented as mean ± standard deviation (SD).
Results:
All three conditions had no significant difference in muscle activation for the bicep Femoris with external upright posture (38.49 ± 9.94 EMGpk), external muscle contraction (38.67 ± 8.18 EMGpk) and the Neutral group (37.55 ± 9.35 EMGpk) When looking at the semitendinosus, again there was no significance with the three attentional focus conditions for muscle activation, External upright posture (51.89 ± 68 10.38 EMGpk), External muscle contraction (49.27 ± 7.56 EMGpk) and the Neutral group (49.66 ± 10.28 EMGpk). Similarly, knee angle remained constant throughout the 3 attentional focus conditions for the Bicep Femoris, Neutral (102.71 ± 5.48°), External muscle contraction (103.16 ± 7.23°) and External upright posture (103.72 ± 4.71°) and for the Semitendinosus, Neutral (103.16° ± 5.36), External muscle contraction (103.55 ± 5.48°) and the External upright posture (104.27° ± 5.05). Post Manipulation checks highlighted that “To what extent were you focused on the movements of any part of your body?” resulted in a score of 3.83 ± 1.03, “To what extent were you focused on hamstring muscle contraction as you executed your NHE?” resulted in a scored 3.92 ± 1 and “To what extent were you focused on maintaining an upright posture as you executed your NHE?” resulted in a scored of 3.58 ± 0.5, highlighting minimal differences noted between conditions.
Discussion: Although the findings highlighted that there were no changes in muscle activation or knee angle during the NHE, the study highlights when NHE are performed they cause a high muscle activation in both the bicep femoris and semitendinosus. The results suggest by performing this type of exercise, it can be an effective tool in injury prevention programmes, in addition to reducing the risk of injury.
