Diagnostic Ultrasound Shows Preferential Activation of Rectus Abdominis Segments with Exercises Targeting Upper Versus Lower Segments.

Preferential activation of rectus abdominis sections during crunch or leg lifts has long been disputed. The objectives of this study were to both explore the activation of the rectus abdominis during these exercises. This study used a randomised independent measures design utilising both EMG and diagnostic ultrasound to record changes in rectus abdominis activity. Fifteen participants each performed multiple repetitions of a 45° crunch, a 90° sit-up, and finally a 90° leg raise, sufficient for an 8-second ultrasound recording utilising M-mode of all four unilateral abdominal segments during each of the exercises, resulting in 12 images per participant. There was a significant interaction between segment number and type of exercise when testing for percent difference (F6, 440 = 4.718, p < .01, η2 = .065). The mean thickness change of abdominis during a crunch manoeuvre was greater than the leg raise by 36.39 ± 3.21 % (p < .01). The mean thickness during the sit-up was also greater than the leg raise (32.49 ± 3.04 %). Rectus abdominis shortening and thickening was observed in all the exercises tested but was most pronounced in the abdominal crunch. Muscle recruitment seems to be biased closer to the load.

Workstation configuration and container type influence upper limb posture in grocery bagging.

INTRODUCTION: Repetitive movements and awkward postures are two persistent injury risk factors for grocery store cashiers. Due to the recent rise in popularity of environmentally-friendly grocery bagging options, current recommendations for cashiers are likely outdated. Correspondingly, the objective of this study was to examine the effects of cashier-specific work demands, workstation configuration, and container type on upper limb postures during typical job activities. METHODS: Fifteen experienced cashiers bagged groceries at varying combinations of workstation height (low, medium, high) and container type (reusable bins, reusable bags, plastic bags). Upper limb movement was quantified with motion capture and amplitude probability distribution functions of humeral elevation and humeral axial internal rotation were used to assess the static (10th percentile), median (50th percentile), and peak (90th percentile) postural demands, which were then interpreted in the context of existing postural guidelines. RESULTS: High workstation height and reusable bags increased right arm elevation at peak posture by 15.7° compared to the low workstation height and reusable bin combination. However, reusable bins increased internal rotation demands of the right arm by 4.3° compared to other container types. Left arm elevation and internal rotation were consistently lower than right arm angles. CONCLUSION: Cashiers are encouraged to adjust the workstation to decrease the arm elevation and internal rotation required by higher workstation heights and tall containers, and to use both arms for scanning and packing, when possible, to reduce undesirable arm postures.

In a dynamic lifting task, the relationship between cross-sectional abdominal muscle thickness and the corresponding muscle activity is affected by the combined use of a weightlifting belt and the Valsalva maneuver.

It has been shown that under isometric conditions, as the activity of the abdominal muscles increases, the thicknesses of the muscles also increase. The purpose of this experiment was to determine whether change in muscle thickness could be used as a measure of muscle activity during a deadlift as well as determining the effect of a weightlifting belt and/or the Valsalva maneuver on the muscle thicknesses. The Transversus Abdominis (TrA) and Internal Obliques (IO) muscles were analyzed at rest and during a deadlift. Muscle thickness was measured using ultrasound imaging and muscle activity was simultaneously recorded using electromyography. Each subject performed deadlift under normal conditions, while performing the Valsalva maneuver, while wearing a weightlifting belt and while both utilizing the belt and the Valsalva maneuver. There was no relationship between change in muscle thickness and muscle activity for both the TrA and IO (R(2)<0.13 for all conditions). However it was found that the Valsalva maneuver increased abdominal muscle thickness whereas the belt limited muscle expansion; each with an increase in activity. These results indicate that ultrasound cannot be used to measure muscle activity for a deadlift and that the belt affects how the IO and TrA function together.

Effect of whole body vibration on the postural control of the spine in sitting.

Stability is defined by the ability to return to the initial (or unperturbed) state following a perturbation and hence can be assessed by quantifying the post-perturbation response. This response may be divided into two phases: an initial passive response phase, dependent upon both the steady state of the system and the system's intrinsic mechanical properties; and a recovery phase, dependent upon active control and reflexes. These two phases overlap and interact with each other. Whole body vibration (WBV) is assumed to influence neuro-sensory functions and perhaps both response stages. The current study observed the effect of WBV on several novel response factors that quantify the two phases in response to an external perturbation. The results indicate a significant effect of vibration exposure on: (1) the normalized maximum distance traveled by center of pressure (COP) from the neutral seated posture, and (2) the normalized time to maximum distance (τ), such that B and τ increased after WBV exposure and decreased after sitting without WBV. These changes may be indicative of passive visco-elastic changes caused by WBV exposure on the spinal tissues which has been indicated as a creep deformation of tissues post-exposure. This change may make the spine vulnerable to injury. Similar trends were noticed in the variables calculated from center of mass data.

Acute effects of whole body vibration on directionality and reaction time latency of trunk muscles: the importance of rest and implications for spine stability.

Workplace exposure to whole body vibration (WBV) has been identified as one of the major physical risk factors encountered by the population. There are indications that, subsequent to a perturbation, impaired reflex response could allow for destabilization of the spine, possibly leading to injury. The purpose of this study was to investigate if WBV alters reflex response of trunk muscles and if the direction of perturbation (flexion or extension or lateral) and delay between exposure and perturbation influences the response. The results indicate that EMG latency was increased more in the vibration condition than in sitting without vibration. Significant effects with respect to directionality were observed in Erector Spinae muscles. The EMG latency reduced from the effect of perturbation after a 20s rest period. Even though the EMG latency did not fully return to its Pre-test state, the present results still show that recovery from the acute effects of WBV is possible with a rest period.

Whole-body vibration experienced by haulage truck operators in surface mining operations: a comparison of various analysis methods utilized in the prediction of health risks.

Whole body vibration (WBV) was measured on eight surface haulage trucks in three size classes (35, 100, 150ton haul capacities). Vibration was measured at the seat/operator interface in accordance with the ISO 2631-1 standard during 1h of normal operation. Highest acceleration readings were observed in the z-axis (vertical). Estimated equivalent daily exposure values in the range of 0.44-0.82 ms(-2) were observed using the frequency-weighted r.m.s method and 8.7-16.4ms(-1.75) using the vibration dose value method. Assessment was carried out using ISO 2631-1 and 2631-5. Operators of surface haulage trucks are regularly exposed to WBV levels that exceed safety limits as dictated by the ISO 2631-1 standard. However, according to ISO 2631-5 the probability of an adverse health effect remains low. These findings confirm an apparent disagreement between the two analysis methods.

Quantification of lumbar stability by using 2 different abdominal activation strategies.

OBJECTIVE: To determine whether the abdominal hollowing technique is more effective for lumbar spine stabilization than a full abdominal muscle cocontraction. DESIGN: Within-subject, repeated-measures analysis of variance was used to examine the effect of combining each of 4 loading conditions with either the hollow or brace condition on the dependent variables of stability and compression. A simulation was also conducted to assess the outcome of a person activating just the transversus abdominis during the hollow. SETTING: Laboratory. PARTICIPANTS: Eight healthy men (age range, 20-33y). INTERVENTIONS: Electromyography and spine kinematics were recorded during an abdominal brace and a hollow while supporting either a bilateral or asymmetric weight in the hands. MAIN OUTCOME MEASURES: Spine stability index and lumbar compression were calculated. RESULTS: In the simulation "ideal case," the brace technique improved stability by 32%, with a 15% increase in lumbar compression. The transversus abdominis contributed .14% of stability to the brace pattern with a less than 0.1% decrease in compression. CONCLUSIONS: Whatever the benefit underlying low-load transversus abdominis activation training, it is unlikely to be mechanical. There seems to be no mechanical rationale for using an abdominal hollow, or the transversus abdominis, to enhance stability. Bracing creates patterns that better enhance stability.

Postural control of the lumbar spine in unstable sitting.

OBJECTIVE: To evaluate the neuromuscular strategy adopted during sitting balance on an unstable surface in the frontal plane. DESIGN: Electromyographic evaluation of trunk muscles. SETTING: University spine biomechanics laboratory. PARTICIPANTS: Seventy asymptomatic men (mean age, 34.5 y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: "Balancers" and "nonbalancers" were identified by principal component analysis of their lumbar spine side flexion angle during sitting balance. Average electromyographic levels were used as a measure of muscle activation. Pearson correlations were used to identify coactivation versus asymmetrical muscle activation of opposite muscle groups. RESULTS: External oblique, internal oblique, and thoracic erector spinae (TES) were most active, and most likely to be used asymmetrically, with other muscles showing low levels of coactivation. Between groups, the average electromyographic levels in the balancers was lower than in the nonbalancers (P<.05), with further differences in the symmetry of external oblique, internal oblique, and TES activation between groups. CONCLUSIONS: Sitting balance in the frontal plane appears to involve a combined feedforward-feedback strategy of muscle activation. Successful balance was characterized by low levels of muscle coactivity, along with higher levels of asymmetric activation in the global trunk muscles, specifically external oblique, internal oblique, and TES.

Relationships between lumbar flexibility, sit-and-reach test, and a previous history of low back discomfort in industrial workers.

The sit-and-reach (S&R) test is often included in standard fitness tests (e.g., Canadian Physical Activity, Fitness and Lifestyle Appraisal [CPAFLA]), justified on the assumption that it is an indicator of low back health. Two issues were examined here: Is low back flexibility linked to having a history of low back disorders? And is the S&R test an indicator of low back flexibility? The relationship between S&R test scores, lumbar range of motion, and having a history of low back discomfort was examined in 72 asymptomatic (at test time) industrial workers (70 M, 2 F; mean age 35 ys; height 1.79 m; mass 84.7 kg). The S&R test, among many collected, was performed according to the CPAFLA guidelines. History of low back discomfort (LBD) was categorized based on whether or not time was lost from work. The S&R test was unable to distinguish between those with a history of LBD and those without. Specific lumbar sagittal range of motion could make this distinction. A moderate correlation (r = 0.42) surfaced between S&R and lumbar flexibility. This study suggests that the value of S&R as an indicator of previous back discomfort is questionable and there may be better indicators for inclusion in the CPAFLA.

Low-back stiffness is altered with warm-up and bench rest: implications for athletes.

INTRODUCTION: General practice in many team sports is to have the athletes who do not start in a game sit on a bench while waiting to play. The purpose of this study was to examine the effect of a warm-up followed by bench rest on the stiffness of the lumbar spine in athletes. METHODS: Nine varsity-level volleyball players volunteered to have their lumbar-spine stiffness measured. The protocol consisted of an initial stiffness measurement followed by a 30-min warm-up, then another stiffness measurement, then 30 min of bench rest, and finally a third stiffness measurement. RESULTS: In general, lumbar spine stiffness increased as a result of bench rest after a warm-up. This effect was seen in both the spine extension and lateral bend axes but not in the flexion or axial twist axes. However, there was no decrease in stiffness associated with the active warm-up portion of the task. CONCLUSIONS: It was concluded that a warm-up followed by bench rest does lead to an increase in stiffness of the lumbar spine, suggesting this practice is not in the best interest of reducing the risk of back injury or optimal performance.