Hip and trunk muscles activity during nordic hamstring exercise

The nordic hamstring exercise (NHE) is a dynamic lengthening ham-string exercise that requires trunk and hip muscles activation. Thigh muscles activation, specifically hamstring/quadriceps contractions has been previously examined during NHE. Trunk and hip muscles activity have not been enough studied. The aim of this study was to analyze of hip and trunk muscles activity during NHE. Surface electromyography (EMG) and kinematic data were collected during NHE. Ten healthy men with the age range of 21-36 years performed two sets of two repetitions with downward and upward motions each of NHE. EMG activity of fif-teen trunk and hip muscles and knee kinematic data were collected. Muscle activity levels were calculated through repeated measure anal-ysis of variance in downward and upward motions, through Paired t-test between downward and upward motions and gluteus maximus to erector spine activity ratio (Gmax/ES ratio) using Pearson correlation analyses were evaluated. Semitendinosus and biceps femoris muscles activity levels were the greatest in both motions and back extensors and internal oblique muscles activity were greater than other muscles (P < 0.05). The decreased Gmax/ES ratio was significantly related to peak knee extension angle in downward (r=0.687) and upward motions (r=0.753) (P < 0.05). These findings indicate the importance of synergis-tic muscles and trunk muscles coactivation in eccentric and concentric hamstrings contractions. It could be important for early assessment of subjects with hamstring injury risk.