Trunk muscle activation in the back and hack squat at the same relative loadsClark, David R1; Lambert, Michael I2; Hunter, Angus M1The Journal of Strength & Conditioning Research: July 12, 2017 - Volume Publish Ahead of Print - Issue - p doi: 10.1519/JSC.0000000000002144 Original Research: PDF Only Buy PAP Abstract Author InformationAuthors Article MetricsMetrics The hack squat (HS) is likely to produce a greater 1 repetition maximum (1RM) compared to the back squat (BS). This can be attributed to the support of the trunk during the HS compared to no support during BS. This support however, may compromise trunk muscle activation (TMA), therefore producing different training adaptations. Accordingly, the purpose of this study was to compare 1RM in BS and HS and TMA at 4 relative loads, 65, 75, 85 and 95% of maximal system mass. Ten males completed 3 test sessions:1) BS and HS 1RM, 2) HS & BS neuromuscular test familiarization, and, 3) Neuromuscular test for 3 reps at 4 loads for BS and HS. BS TMA was significantly greater (p<0.05) than HS for all muscles and phases except rectus abdominus in concentric phase. TMA increased (p<0.05) with load in all muscles for both exercises and phases apart from lumbar sacral erector spinae in HS eccentric phase. Mean HS 1RM and submaximal loads were significantly (p<0.0001) higher than the equivalent BS loads. Duration of the eccentric phase was higher (p<0.01) in HS than BS but not different in concentric phase. Duration increased significantly (p<0.01) with load in both exercises and both phases. Despite higher absolute tests loads in HS, TMA was higher in BS. TMA is sensitive to load in both exercises. BS is more effective than HS in activating the muscles of the trunk and therefore arguably more effective in developing trunk strength and stability for dynamic athletic performance. 1Physiology, Exercise and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, UK. 2Division of Exercise Science and Sports Medicine, University of Cape Town, Department of Human Biology, Cape Town, South Africa. Corresponding Author: David R Clark 38 Montgomery Crescent, Dunblane, FK15 9FB, United Kingdom Phone number: +44 (0) 1786 466098 Email address: email@example.com Copyright © 2019 by the National Strength & Conditioning Association.