Janessa D.M. Drake

Investigation of trunk muscle co-contraction and its association with low back pain development during prolonged sitting.

Previous work has shown muscle activation differences between chronic low back pain patients and healthy controls in sitting postures, and between asymptomatic individuals who do (PDs: pain developers) and do not (NPDs: non-pain developers) develop transient back pain during prolonged standing (as determined using a visual analog scale). The current study aimed to investigate differences in trunk muscle co-contraction between PD and NPD individuals over 2h of prolonged sitting. Ten healthy males sat continuously for 2h while performing tasks that simulated computer-aided-drafting; four were classified as PDs, and six as NPDs. Co-contraction indices were calculated from EMG data collected from eight trunk muscles bilaterally, and compared between pain groups and over time. PDs exhibited higher levels of co-contraction than NPDs. Additionally, co-contraction tended to increase over time, and was significantly correlated to pain development. The relationship between co-contraction and back pain development may actually be circular, in that it is both causal and adaptive: high co-contraction initially predisposes to pain development, following which co-contraction further increases in an attempt to alleviate the pain, and the cycle perpetuates. Further work will be required to elucidate the exact nature of this relationship, and to confirm the generalizability to other populations.

Which motion segments are required to sufficiently characterize the kinematic behavior of the trunk

Various kinematic definitions of the thoracic spine have been employed in past work. However, the segments necessary to sufficiently characterize the thoracic spine during trunk movements in all three planes of motion have not yet been identified. This study aimed to determine the minimum number of segments necessary to adequately characterize the kinematics of the thoracic spine. Thirty individuals, asymptomatic for back pain, performed ten trials of maximum trunk flexion, lateral bend, and axial twist; thoracic flexion, lateral bend, and axial twist; and slumped standing. Marker clusters were applied over the C(7), T(3), T(6), T(9), T(12), and L(5) vertebrae. Three-dimensional angles of each cluster were calculated, and cross-correlation (R(xy(time))) and correlation (R(xy(max))) analyses were employed to assess the relationships in the motion patterns and maximum angles of adjacent clusters, respectively. The motion patterns and maximum angles of adjacent clusters were very strongly (R(xy(time)) > 0.90 for 26 of 35 pairings) and strongly (R(xy(max)) > 0.80 for 25 of 35 pairings) correlated, respectively. A four-cluster set (C(7), T(6), T(12), and L(5)) represented thoracic movement for six of the seven movement tasks tested. These results provide insight into thoracic movement coordination, with implications for predictive spinal modeling and clinical assessment practices.

What is slumped sitting? A kinematic and electromyographical evaluation

Slumped sitting is a commonly used reference posture when comparing effects of upright sitting in both clinical and non-clinical populations alike. The exact nature of slumped sitting has not been clearly defined, including regional differences within the posture, and how the passive nature of slumped sitting compares to an active-flexion posture. Kinematic and electromyographical (EMG) data were collected from 12 males during three repeats of slumped sitting and seated maximum forward flexion. Spine angles were defined in four regions (three thoracic and lumbar) as well as for the pelvis, and EMG was collected from eight muscles bilaterally. Kinematic data were expressed as a range of motion (in degrees), and as a percent of full forward flexion while seated (%SIT-FF) and standing (%STAND-FF). EMG data were normalized to a percent maximum contraction (%MVC). Results showed that slumped sitting is characterized by 10° posterior pelvis rotation, near end-range flexion of the mid- (90%SIT-FF) and lower- (81%SIT-FF) thoracic regions, and mid-range flexion of the upper-thoracic (51%SIT-FF) and lumbar (43%SIT-FF) regions. Comparison of slumped by %STAND-FF showed the upper- and mid-thoracic regions to have high variability and large values (over 100%STAND-FF). Muscle activation showed a significant 3%MVC reduction in the lower-thoracic erector spinae muscle when moving from upright to slumped sitting. These data highlight the postural differences occurring within different spine regions, and interpretations that could be drawn, depending on which normalization (sit or stand) method is used.

Transient pain developers show increased abdominal muscle activity during prolonged sitting.

BACKGROUND Sitting is a commonly adopted posture during work and prolonged exposures may have detrimental effects. Little attention has been paid to the thoracic spine and/or multiple axes of motion during prolonged sitting. Accordingly, this study examined three-dimensional motion and muscle activity of the trunk during two hours of uninterrupted sitting. METHODS Ten asymptomatic males sat during a simulated office task. Kinematics were analyzed from six segments (Neck, Upper-, Mid-, and Lower-thoracic, Lumbar, and Pelvis) and electromyography was recorded from eight muscles bilaterally. RESULTS Four participants developed transient pain. These participants showed higher average muscle activations in the abdominal muscles. Additionally, the non-pain group showed less lateral bend positional change in the mid-thoracic region compared to the upper- and lower-thoracic regions. Weak-to-moderate positive correlations were also found between rated pain and low back muscle activation. DISCUSSION The results provided further evidence of reduced movement in non-pain developers and altered muscle activation patterns in pain developers. Low-level, prolonged static contractions could lead to an increased risk of injury; and though the increased abdominal activity in the pain developers was not directly associated with increased rated pain scores, this could indicate a pre-disposition to, or enhancer of, transient pain development.

Repeatability of kinematic and electromyographical measures during standing and trunk motion: How many trials are sufficient?

Previous studies have recommended a minimum of five trials to produce repeatable kinematic and electromyography (EMG) measures during target postures or contraction levels. This study aimed to evaluate the repeatability and reliability of kinematic and EMG measures that are of primary interest in the investigation of trunk movement, and to determine the number of trials required to achieve repeatability and reliability for these measures. Thirty participants performed ten trials of upright standing and maximum trunk ranges-of-motion. Mean (upright standing) and maximum (movement tasks) kinematic and EMG measures were assessed using intraclass correlation coefficients and standard error of measurement, which were used to identify the minimum number of trials for each measure. The repeatability and reliability of the measures were generally high, with 64%, 77%, 85%, and 92% of measures producing repeatable and reliable values with two, three, four, and five trials, respectively. Ten trials were not sufficient for several upright standing angle measures and maximum twist lumbar angles. Further, several abdominal muscles during maximum flexion, as well as the left lower-thoracic erector spinae during maximum twist, required as many as five trials. These measures were typically those with very small amounts of motion, or muscles that did not act in the role of prime mover. These results suggest that as few as two trials may be sufficient for many of the kinematic and EMG measures of primary interest in the investigation of trunk movement, while the collection of four trials should produce repeatable and reliable values for over 80% of measures. These recommendations are intended to provide an acceptable trade-off between repeatable and reliable values and feasibility of the collection protocol.

Head and Arm Positions that Elicit Maximal Voluntary Trunk Range-of-Motion Measures

Relationships have been shown between spinal motion and head and arm postures, yet there has been little standardization of the head and arm positions that elicit maximal voluntary spine angles during maximal trunk flexion, lateral bend, and axial twist. This study aimed to determine the head and arm positions that facilitated maximum voluntary range of motion in various spinal regions during these movements. Twenty-four individuals performed maximal movements in each plane with different combinations of head and arm positions (flexion and lateral bend: four combinations; axial twist: six combinations). Generally, greater angles were elicited for the upper spine regions when the head was moved in the direction of trunk motion, while the angles of the lower regions were either unaffected or greater when the head was kept in a neutral position. Arm positions also affected maximum spinal angles, in that angles were greatest when the arms were hanging to the floor (flexion), abducted to 90° (axial twist), and either hanging to the floor or crossed over the chest (lateral bend). These findings provide insight into the interplay between the spine and adjacent segments and constitute an initial attempt to develop standardized positions during maximum range-of-motion trials.

Location of Instability During a Bench Press Alters Movement Patterns and Electromyographical Activity.

Abstract Nairn, BC, Sutherland, CA, and Drake, JDM. Location of instability during a bench press alters movement patterns and electromyographical activity. J Strength Cond Res 29(11): 3162–3170, 2015—Instability training devices with the bench press exercise are becoming increasingly popular. Typically, the instability device is placed at the trunk/upper body (e.g., lying on a Swiss ball); however, a recent product called the Attitube has been developed, which places the location of instability at the hands by users lifting a water-filled tube. Therefore, the purpose of this study was to analyze the effects of different instability devices (location of instability) on kinematic and electromyographical patterns during the bench press exercise. Ten healthy males were recruited and performed 1 set of 3 repetitions for 3 different bench press conditions: Olympic bar on a stable bench (BENCH), Olympic bar on a stability ball (BALL), and Attitube on a stable bench (TUBE). The eccentric and concentric phases were analyzed in 10% intervals while electromyography was recorded from 24 electrode sites, and motion capture was used to track elbow flexion angle and 3-dimensional movement trajectories and vertical velocity of the Bar/Attitube. The prime movers tended to show a reduction in muscle activity during the TUBE trials; however, pectoralis major initially showed increased activation during the eccentric phase of the TUBE condition. The trunk muscle activations were greatest during the TUBE and smallest during the BAR. In addition, the TUBE showed decreased range of elbow flexion and increased medial-lateral movement of the Attitube itself. The results further support the notion that instability devices may be more beneficial for trunk muscles rather than prime movers.

Evaluation of the Lumbar Kinematic Measures That Most Consistently Characterize Lumbar Muscle Activation Patterns During Trunk Flexion: A Cross-Sectional Study

OBJECTIVE The purpose of this study was to determine which kinematic measure most consistently determined onset and cessation of the flexion-relaxation response. METHODS The study was a cross-sectional design in a laboratory setting in which 20 asymptomatic university-aged (19.8-33.3 years old) participants were tested. Muscle activation was measured for the lumbar erector spinae, and 3-dimensional motion was recorded. Flexion-relaxation onset and cessation occurrences were determined for 10 standing maximum voluntary flexion trials. The lumbar and trunk angles at both events were expressed as unnormalized (°) and normalized (%Max: percentage of maximum voluntary flexion) measures. Intraclass correlation coefficients and coefficients of variation were calculated to determine within- and between-participant reliability, respectively. RESULTS Mean (SD) unnormalized flexion-relaxation angles ranged from 46.28° (11.63) (lumbar onset) to 108.10° (12.26) (trunk cessation), whereas normalized angles ranged from 71.31%Max (16.44) (trunk onset) to 94.83%Max (lumbar cessation). Intraclass correlation coefficients ranged from 0.905 (normalized lumbar, left side, onset) to 0.995 (unnormalized lumbar, both sides, cessation). Coefficients of variation ranged from 3.56% (normalized lumbar, right side, cessation) to 26.02% (unnormalized trunk, left side, onset). CONCLUSIONS The data suggest that, for asymptomatic individuals, unnormalized and normalized lumbar kinematics most consistently characterized flexion-relaxation angles within and between participants, respectively. Lumbar measures may be preferential when the flexion-relaxation response is investigated in future clinical and biomechanical studies.

Differences in lumbopelvic control and occupational behaviours in female nurses with and without a recent history of low back pain due to back injury

Low back pain is highly prevalent in nurses. This study aimed to determine which physical fitness, physical activity (PA) and biomechanical characteristics most clearly distinguish between nurses with [recently injured (RInj)] and without [not recently injured (NRInj)] a recent back injury. Twenty-seven (8 RInj, 19 NRInj) female nurses completed questionnaires (pain, work, PA), physical fitness, biomechanical and low back discomfort measures, and wore an accelerometer for one work shift. Relative to NRInj nurses, RInj nurses exhibited reduced lumbopelvic control (41.4% more displayed a moderate loss of frontal plane position), less active occupational behaviours (less moderate PA; less patient lifts performed alone; more sitting and less standing time) and more than two times higher low back discomfort scores. Despite no physical fitness differences, the lumbopelvic control, occupational behaviours and discomfort measures differed between nurses with and without recent back injuries. It is unclear whether poor lumbopelvic control is causal or adaptive in RInj nurses and may require further investigation. Practitioner Summary: It is unclear which personal modifiable factors are most clearly associated with low back pain in nurses. Lumbopelvic control was the only performance-based measure to distinguish between nurses with and without recent back injuries. Future research may investigate whether reduced lumbopelvic control is causal or adaptive in recently injured nurses.

Sequencing of superficial trunk muscle activation during range-of-motion tasks.

Altered lumbo-pelvic activation sequences have been identified in individuals with low back pain. However, an analysis of activation sequences within different levels of the trunk musculature has yet to be conducted. This study identified the activation sequences characteristic of the trunk musculature during upright standing and range-of-motion tasks. Surface electromyography was recorded for eight trunk muscles bilaterally during trunk range-of-motion movement tasks in 30 participants. Cross-correlation was performed on 48 pairings of muscles, consisting of one lower- and one mid-level muscle, or one mid-level and one upper muscle. Time lags of the maximum cross-correlation coefficient were extracted and defined as a top-down or bottom-up activation sequence, or similar activation timing. Pairings that demonstrated a specific activation sequence in 50% or more of participants were then identified. Similar activation timing was consistently identified between muscle pairings for upright standing. Top-down sequences and similar timing were identified for abdominal - mid-level pairings in maximum flexion and slumped standing, respectively, while both tasks were characterized by bottom-up sequences when considering the lumbar and lower-thoracic erector spinae. Sequences were more variable across muscle pairings for lateral bend and axial twist tasks. These results provide insight into the synergy of the trunk musculature for movements in the three planes of motion. These findings can be used for comparison to low back pain populations, as altered activation sequences in these individuals may contribute to maladaptive loading patterns and consequently the development or exacerbation of low back pain.