Study design: Different factorial designs analyzing the same data were compared for consistent interpretation.
Objective: To assess hand dominance as an explanatory factor when comparing dominant and nondominant side back muscle response time delay and fatigability.
Summary of background data: A number of studies have evaluated lumbar spinal muscle responses to sudden load and fatigue. Although the dominant side of the back is usually determined by considering hand dominance, few studies explicitly consider hand dominance as part of the explanatory model and assume that right- and left-handed patients are not unique cohorts. METHODS.: The erector spinae and multifidi lumbar muscle groups in patients with chronic low back pain (CLBP) were investigated. For the response time to a sudden load, the biceps brachii muscle was compared with erector spinae and multifidi muscles to understand any compensatory upper extremity movement patterns. For fatigue, the erector spinae and multifidi muscle median frequency (MF) and its slope (MFS) were measured during a 1-minute isometric back extension maneuver.
Results: Altogether, 46 patients with CLBP were studied. Right- and left-handed subjects did not differ in reported disability based on the Oswestry Disability Index, (F1, 44 = 2.11, P < 0.153). The dominant and nondominant side response times were significantly different for left-handed patients but not for right-handed patients. The nondominant side back muscles, located on the contralateral side of the dominant hand, were faster for the right-hand dominant patients and slower for the left-hand dominant patients. In the muscles on the nondominant side of the back, the left-hand dominant patients demonstrated significantly more fatigue than right-hand dominant patients. However, in the muscles on the dominant side of the back, neither set of patients demonstrated fatigability.
Conclusions: When examining differential lumbar muscle responses, failing to consider hand dominance explicitly in conjunction with the side assessed resulted in confounding effects. The results of the study indicated a delayed back muscle response time on the nondominant side. This delayed response time raises the possibility that unbalanced muscle activity could prompt a decreased, uncoordinated, asymmetric bracing effect, thereby increasing the risk of lumbar segment buckling. Further studies are needed to investigate the characteristics of the back muscles on the same side of the dominant hand and the factors mediating neuromuscular differences in patients with CLBP. Understanding the effects of hand dominance on fatigue in certain back muscles should lead to better treatments thereby improving neuromuscular control in patients with CLBP.