Altered muscle recruitment during extension from trunk flexion in low back pain developers

Background

A functionally induced, transient low back pain model consisting of exposure to prolonged standing has been used to elucidate baseline neuromuscular differences between previously asymptomatic individuals classified as pain developers and non-pain developers based on their pain response during a standing exposure. Previous findings have included differences in frontal plane lumbopelvic control and altered movement strategies that are present prior to pain development. Control strategies during sagittal plane movement have not been previously investigated in this sample. The purpose of this research was to investigate neuromuscular control differences during the extension phase from trunk flexion between pain developers and non-pain developers.

Methods

Continuous electromyography and kinematic data were collected during standing trunk flexion and extension on 43 participants (22 male) with an age range of 18–33 years, prior to entering into the prolonged standing exposure. Participants were classified as pain developer/non-pain developer by their pain response (≥ 10 mm increase on a 100 mm visual analog scale) during standing. Relative timing and sequencing data between muscle pairs were calculated through cross-correlation analyses, and evaluated by group and gender.

Findings

Pain developers demonstrated a ‘top-down’ muscle recruitment strategy with lumbar extensors activated prior to gluteus maximus, while non-pain developers demonstrated a typical ‘bottom-up’ muscle recruitment strategy with gluteus maximus activated prior to lumbar extensors.

Interpretation

Individuals predisposed to low back pain development during standing exhibited altered neuromuscular strategies prior to pain development. These findings may help to characterize biomechanical movement profiles that could be important for early identification of people at risk for low back pain.     

Gender-based differences in postural responses to seated exposures

Background. Individuals may respond differently to various chair designs and the factors that influence these sitting behaviours are not well understood. There is very little information in the scientific literature regarding the observation and documentation of gender differences in seated postures. In particular, anecdotal observations of potential gender-specific sitting behaviours led us to test the influence of gender on the postural responses to different seated conditions.

Methods. Sixteen healthy university students (8 males and 8 females) were tested on four different chair configurations. Upper body kinematics (spine angles and centre of mass) and seat pressure profiles (centre of pressure, peak pressure) were obtained during each testing session.

Findings. Regardless of the chair used or the task performed, average lumbar and trunk angles were significantly more flexed for males than for females (P = 0.047 and P = 0.0026, respectively). Males exhibited average lumbar spine and trunk angles of 65.4° (SD 16.2°) and 29.8° (SD 28.3°), respectively, while female lumbar spine and trunk angles were 49.6° (SD 23.1°) and −3.3° (SD 20.4°), respectively. The pelvis was posteriorly rotated for males (7.6° (SD 8.2°)) and anteriorly rotated for females (−5.5° (SD 9.3°)) (P = 0.0008). Significant gender * chair interactions of the location of the individual on the chair seat were most marked for the pivoting chair with a back rest. Females positioned their centre of mass and hip joints anterior to the chair pivot point while males’ centre of mass (P = 0.0003) and hip joints (P = 0.0039) were located posterior to the pivot point. Females also sat with their centre of mass closer to the seat pan centre of pressure than males when a back rest was present (P = 0.0012).

Interpretation. Males and females may be exposed to different loading patterns during prolonged sitting and may experience different pain generating pathways. Therefore, gender-dependent treatment modalities and/or coaching should be implemented when considering methods of reducing the risk of injury or aggravation of an existing injury.