Specific phase related patterns of trunk muscle activation during lateral lifting and lowering

Influence of trunk muscle activity and stability in front and back holding

PURPOSE

A tandem carrying style is often used in the workplace, but carrying approaches are different for two people because of the holding load in the tandem posture. To understand these carrying styles, this study aimed to investigate the patterns of muscle activity and stability of the trunk influenced by front and back holding of a heavy load.

METHODS

Electromyography data of eight trunk and two hip muscles, as well as displacements of the trunk, were recorded for analysis while subjects stood statically holding a handle in the front and back of the body with and without load.

RESULTS

Without load, muscle activities during front holding mirrored those during back holding. With load, greater muscle activities were observed in the dorsal muscles of the trunk and lesser activities were noted in the ventral muscles in the two holding styles. More frequencies of trunk oscillations occurred in front holding with and without load.

CONCLUSIONS

The results revealed that back holding of load created more stability of the upper body, whereas front holding resulted in more instability of the trunk.

Changes in deep abdominal muscle thickness during common trunk-strengthening exercises using ultrasound imaging

STUDY DESIGN

Cross-sectional study design.

OBJECTIVES

To characterize changes in muscle thickness in the transversus abdominis (TrA) and internal oblique (IO) muscles during common trunk-strengthening exercises, and to determine whether these changes differ based on age.

BACKGROUND

Although trunk-strengthening exercises have been found to be useful in treating those with low back pain (LBP), our understanding of the relative responses of the TrA and IO muscles during different exercises is limited.

METHODS AND MEASURES

Six commonly prescribed trunk-strengthening exercises were performed by 120 subjects (40 subjects per age group: 18-30, 31-40, and 41-50 years). Ultrasound imaging was used to measure the thickness of the TrA and IO during the resting and contracted state of each exercise. The average thickness of the muscles while in the contracted position was divided by the thickness values in the resting position for each exercise, based on 2 performances of each exercise. Two 3-by-6 repeated-measures analyses of variance were used to determine significant changes in muscle thickness of the TrA and IO, based on age group and exercise performed.

RESULTS

For both muscles, the trunk exercise-by-age interaction effect (TrA, P = .358; IO, P = .217) and the main effect for age (TrA, P = .615; IO, P = .219) were not significant. A significant main effect for trunk exercise for both muscles (P<.001) was found. The horizontal side-support (mean +/- SD contracted-rest thickness ratio: TrA, 1.95 +/- 0.69; IO, 1.88 +/- 0.52) and the abdominal crunch (mean +/- SD contracted-rest thickness ratio: TrA, 1.74 +/- 0.48; IO, 1.63 +/- 0.41) exercises resulted in the greatest change in muscle thickness for both muscles. The abdominal drawing-in maneuver (mean +/- SD contracted-rest thickness ratio: TrA, 1.73 +/- 0.36; IO, 1.14 +/- 0.33) and quadruped opposite upper and lower extremity lift (mean +/- SD contracted-rest thickness ratio: TrA, 1.59 +/- 0.49; IO, 1.25 +/- 0.36) exercises resulted in changes in TrA muscle thickness with minimal changes in IO muscle thickness.

CONCLUSION

Changes in TrA and IO muscle thickness differed across 6 commonly prescribed trunk-strengthening exercises among healthy subjects without LBP. These differences did not vary by age. This information may be useful for informing exercise prescription.

Quadratus Lumborum Asymmetry and L4 Pars Injury in Fast Bowlers

PURPOSE

This prospective study examined the association between quadratus lumborum (QL) asymmetry and the development of symptomatic pars interarticularis lesions in the lumbar spine of adolescent cricket fast bowlers.

METHODS

Annual magnetic resonance imaging was used to measure QL volume asymmetry and for identifying pars lesions of the lumbar vertebrae in fast bowlers (N=51) and a control group of swimmers (N=18). Manual segmentation of axial images spanning the lumbar spine was performed to calculate percent QL asymmetry relative to the bowling- or throwing- (swimmers) arm side. Asymmetry above 100% indicated a larger QL volume on the bowling- (throwing) arm side.

RESULTS

The mean QL asymmetry in bowlers of 110.5% (SD=12.1%) was significantly different from the 96.6% (SD=5.0%) asymmetry in swimmers (t=6.75, P<or=0.001). In bowlers with symptomatic unilateral L4 pars lesions (N=11), which all developed opposite the bowling-arm side, the mean 124.3% (SD=8.3%) QL asymmetry exceeded the 106.7% (SD=10.1%) asymmetry in bowlers without these one-sided lesions. A logistic regression model (intercept=-22.1, P<or=0.001; asymmetry coefficient=0.18, P<or=0.001) demonstrated a significant association between increasing QL asymmetry and L4 lesions in bowlers. Receiver operating characteristic curve analysis demonstrated that QL asymmetry was an excellent predictor of L4 lesions in fast bowlers (area under curve=0.89, 95% confidence interval: 0.79, 0.98).

CONCLUSION

The strong association between QL asymmetry and the development of symptomatic unilateral L4 pars lesions in adolescent bowlers conceivably reflects a mechanical coupling between the loading milieu generating these injuries and preferential hypertrophy of this paraspinal muscle in response to repetitive activation during fast bowling.

Forearm electromyographic changes with the use of a haptic force-feedback computer mouse

OBJECTIVE

To examine changes in biomechanical and motor control associated with a force-feedback computer mouse.

BACKGROUND

Haptic computer mice can improve the movement times for point-and-click tasks; however, changes in upper extremity biomechanics and motor control are unknown.

METHOD

Eighteen people (ages 22-37 years) performed a point-and-click task 80 times using a force-feedback computer mouse across three different conditions: (a) no force feedback, emulating a conventional mouse; (b) a single attractive force field at the desired target that pulls the mouse to the center of the target; and (c) an attractive force field at the desired target as well as others between the two possible targets, distracting the user from the intended target. Cursor kinematics, wrist posture, and electromyographic (EMG) forearm muscle activity were recorded.

RESULTS

The point-and-click movements were 30% faster with the addition of a single force field and 3% faster with the addition of multiple force fields. The Fitts' law index of performance metrics improved from 2.9 bits/response to 4.1 bits/response for multiple attractive fields and to 6.0 bits/response for a single force field. For the distracting force fields, the cursor maximum velocities were over 50% faster. EMG amplitude values were largest for the distracting force fields. These data suggest that the operator uses increased muscle activity to accelerate the mouse through the distracting force fields.

CONCLUSION

When implementing attractive haptic force fields, one needs to consider how to reduce these observed effects of potential distracting force fields.

APPLICATION

Applications include human-computer interface design for pointing devices extensively used for the graphical user interface.