title: Nonlinear Analysis of an Unstable Bench Press Bar Path and Muscle Activation.
abstract: Lawrence, MA, Leib, DJ, Ostrowski, SJ, and Carlson, LA. Nonlinear analysis of an unstable bench press bar path and muscle activation. J Strength Cond Res 31(5): 1206-1211, 2017-Unstable resistance exercises are typically performed to improve the ability of stabilizing muscles to maintain joint integrity under a load. The purpose of this study was to examine the effects of an unstable load (as provided by a flexible barbell and a load suspended by elastic bands) on the bar path, the primary musculature, and stabilizing musculature while bench pressing using nonlinear analyses. Fifteen resistance-trained men (age 24.2 ± 2.7 years, mass 84.1 ± 12.0 kg, height 1.77 ± 0.05 m, 9.9 ± 3.4 years of lifting experience, and bench press 1 repetition maximum (RM) 107.5 ± 25.9 kg) volunteered for this study. Subjects pressed 2 sets of 5 repetitions in both stable (total load 75% 1RM) and unstable (total load 60% 1RM) conditions using a standard barbell and a flexible Earthquake bar, respectively. Surface electromyography was used to detect muscle activity of primary movers (pectoralis major, anterior deltoid, and triceps) and bar stabilizing musculature (latissimus dorsi, middle and posterior deltoid, biceps brachii, and upper trapezius). During the unstable condition, the bar moved in more ways and was less predictable in the mediolateral and anteroposterior directions. However, the muscle activation patterns of all muscles were more constrained with the unstable barbell. These findings suggest that the unstable condition was more challenging to control, but subjects controlled the instability by contracting their muscles in a more stable pattern or "staying tight" throughout the exercise.
authors.affiliation: 1Department of Physical Therapy, University of New England, Portland, Maine; 2Department of Orthopaedic Surgery, Washington University, St. Louis, Missouri; 3Department of Exercise and Sport Performance, University of New England, Portland, Maine; and 4Center for Excellence in the Neurosciences, University of New England, Biddleford, Maine.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Lawrence
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Leib
authors.forename: Stephanie J
authors.initials: SJ
authors.lastname: Ostrowski
authors.forename: Lara A
authors.initials: LA
authors.lastname: Carlson
mesh_terms: D000328:Adult; D057645:Deltoid Muscle / Q000502:physiology; D004576:Electromyography; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000502:physiology*; D017711:Nonlinear Dynamics; D010369:Pectoralis Muscles / Q000502:physiology; D064171:Superficial Back Muscles / Q000502:physiology; D014891:Weight Lifting / Q000502:physiology*; D055815:Young Adult