Cross Education; : The effect of 10 weeks of unilateral resistance training on strength and hypertrophy

Sammanfattning: Abstract    Aim    The main purpose of this study was to investigate Cross Education (CE), and how gender, detraining and leg dominance affects CE in previously untrained subjects when conducting a unilateral resistance training program. We also investigated if unilateral resistance training can give a hypertrophic response.    Method   Twenty healthy previously untrained individuals, 10 females and 10 males, were recruited as volunteer participants. The participants were randomly assigned to train either left or right leg. The training intervention was 10 weeks (34 sessions) of unilateral resistance training in the leg press and leg extension, sixteen of the participants fulfilled the criteria for inclusion. After two initial familiarization the participants trained conventional resistance training three times a week (week 1-3, 5-7 and 9-10) and Blood Flow Restriction Training (BFRT) five times a week (week 4 and 8). One repetition maximum for both legs in the leg press and leg extension was tested pre-, post and post20 to the training intervention as well as ultrasound measurements of muscle thickness.   Results    The ten-week training period resulted in a significant increase of maximal strength for the untrained leg 18,9 %, (16,6) (p < 0,01) in the leg press and 6,7 %, (3,7) (p < 0,05) in the leg extension. When comparisons between gender were made only men had a significant increase 26,5 %, (16,7) (p < 0,01) in the leg press and 9,9 %, (4,7) (p < 0,05) in the leg extension. Also, we saw a significant difference between women and men on a group level. Comparisons of dominant vs non-dominant leg showed that training the dominant leg resulted in a significant increase of maximal strength in the untrained leg in both the leg press 22 %, (17,9) (p < 0,01) and leg extension 10,1 %, (4,3) (p < 0,05). The maximal strength in the untrained leg was not significantly altered by the detraining period and a significant increase of muscle thickness could be seen in the untrained leg at MP50 4,7 %, (1,3) (p < 0,01).   Conclusion    The conclusions are that a ten week unilateral resistance training intervention results in a CE effect for men but not for women and that this type of training also can result in an increased muscle thickness in the untrained leg. Our findings also supports that training the dominant limb has superior effect on achieving a CE effect. Lastly we conclude that a twenty week detraining period did not affect the CE achieved strength.