Time dependent spine stability: the wise old man and the six blind elephants

The Effect of Tactical Tasks and Gear on Muscle Activation of SWAT Officers

ABSTRACT

Keeler, JM, Pohl, MB, Bergstrom, HC, Thomas, JM, and Abel, MG. The effect of tactical tasks and gear on muscle activation of SWAT officers. J Strength Cond Res 36(1): 238-244, 2022-Special Weapons and Tactics (SWAT) officers perform a variety of tactical operations while wearing tactical gear. Load carriage has been shown to alter muscle activation in the torso and is also associated with lower back pain, which is a prevalent musculoskeletal injury suffered by SWAT Officers. The purpose of this study was to quantify the effect of tactical gear on muscle activation of torso musculature while performing occupational tasks. Twenty male SWAT Officers (age: 34.7 ± 4.5 years; height: 1.79 ± 0.1 m; body mass: 91.5 ± 17.3 kg) performed 4 tasks (standing, rifle walk, sitting, and shield walk) with and without gear (mass of gear: 13.8 ± 1.9 kg). Mean electromyographic amplitude was evaluated bilaterally for the erector spinae, rectus abdominis, and external oblique muscles during the trials and expressed relative to maximal voluntary isometric contraction (MVIC). Addition of gear significantly increased erector spinae mean muscle activation during the rifle walk task (mean delta: +0.16%). However, no differences in muscle activation were identified for any other muscles between gear conditions (effect size ≤ 0.15). The shield walk produced the highest mean activation for each muscle during different tasks. The dynamic tasks yielded (0.24-4.18% MVIC) greater muscle activation levels than sitting and standing tasks. Despite minimal increases in muscle activation levels with the addition of gear, load carriage is known to increase the risk of acute and chronic injury. Collectively, these findings indicate that SWAT Officers should perform most skills without gear during tactical training to simulate task-specific movement patterns but reduce the risk of musculoskeletal injury.

Efficacy of six months neuromuscular exercise on lumbar movement variability - A randomized controlled trial

INTRODUCTION

Lumbar movement variability during heavy, repetitive work may be a protective mechanism to diminish the progression of lumbar disorders and maintain neuromuscular functional integrity. The effect of neuromuscular exercise (NME) on the variability of lumbar movement is still to be determined.

METHODS

A randomised controlled trial was conducted on a population of nursing personnel with subacute LBP. Following randomization, the NME group participants completed an NME program of six months duration. The participants in the control group only attended the assessment sessions. The outcomes were assessed at: baseline; after six months intervention; 12 months. The primary outcome was lumbar movement variability based on angular displacement and velocity.

RESULTS

A positive treatment effect on lumbar movement variability was seen after six months of NME intervention. Angular displacement improved, and angular velocity remained constant. At the 12-month follow up, however, the effect faded in the NME group. Lumbar movement variability worsened in the control group over all time periods.

CONCLUSION

NME may improve lumbar movement variability in the short term and may indicate improved neuromuscular functional integrity. The design of an optimal NME program to achieve long-term improvement in lumbar movement variability is a subject worthy of further research.

Twelve-year follow-up of a randomized controlled trial of comprehensive physiotherapy following disc herniation operation

Objective:

To evaluate the long-term effects of postoperative comprehensive physiotherapy starting one week after lumbar disc surgery.

Design:

Twelve-year follow-up of a three-armed, randomized, controlled, single-blinded clinical trial.

Setting:

Department of Physical Medicine & Rehabilitation.

Participants:

Of 111 patients following first-time, uncomplicated lumbar disc surgery who participated in the original study and completed the treatment originally allocated, 74 ((67%; 29 (73%) physiotherapy, 22 (58%) sham therapy, 23 (68%) no therapy) completed a 12-year follow-up examination.

Interventions:

In the original study, patients had been randomly assigned to comprehensive physiotherapy, sham intervention (neck massage), or no therapy.

Measures:

Low Back Pain Rating Scale; best score 0, worst score 130 points).

Results:

At 12 years after surgery, the group participating in comprehensive physiotherapy had significantly better functional outcomes, as rated on the Low Back Pain Rating Score, than the untreated group (mean difference: −13.2 (95% CI: (−25.4; −1.0)). Equally, there was a clinically relevant, non-significant difference between the sham therapy and no therapy (mean difference: −12.5 (95%CI: −26.1; 1.1)). Consequently, the Low Back Pain Rating Score outcome did not differ between physiotherapy and sham therapy (mean difference: −0.7 (95%CI: −14.2; 12.8)).

Conclusions:

Participating in a comprehensive physiotherapy program following lumbar disc surgery may be associated with better long-term health benefits over no intervention, but may not be superior to sham therapy.

Low amplitude characterization tests conducted at regular intervals can affect tendon mechanobiological response

In bioreactor studies of tissue mechanobiology, characterizing changes in tissue quality is essential for understanding and predicting the response to mechanical stimuli. Unfortunately, current methods are often destructive and cannot be used at regular intervals on the same sample to characterize progression over time. Non-destructive methods such as low amplitude stress relaxation tests could be used, but then, the following dilemma comes into play: how can we accurately measure live tissue progression over time if the tissue is reacting to our measurement methods? In this study, we investigated the hypothesis that stress relaxation tests at physiological amplitudes conducted at regular intervals between stimulation periods do not modify tissue progression over time. Live, healthy tendons were subjected to mechanical stimuli inside a bioreactor for 3 days. The tendons were grouped based on the daily characterization protocol (24 or 0 stress relaxation tests) and their progression over time were compared. Stress relaxation tests at physiological amplitudes modified the tendon response to mechanical stimulation as observed through mechanical and histologic analyses. Possible solutions to eliminate or minimize the effect of stress relaxation tests are to use the mechanical stimuli to characterize tissue progression or to limit the number of stress relaxation tests.

The decreased responsiveness of lumbar muscle spindles to a prior history of spinal muscle lengthening is graded with the magnitude of change in vertebral position

In the lumbar spine, muscle spindle responsiveness is affected by the duration and direction of a lumbar vertebra's positional history. The purpose of the present study was to determine the relationship between changes in the magnitude of a lumbar vertebra's positional history and the responsiveness of lumbar muscle spindles to a subsequent vertebral position and subsequent vertebral movement. Neural activity from multifidus and longissimus muscle spindle afferents in deeply anesthetized cats was recorded while creating positional histories of the L(6) vertebra. History was induced using a displacement-controlled feedback motor. It held the L(6) vertebra for 4 s at an intermediate position (hold-intermediate at 0 mm) and at seven positions from 0.07 to 1.55 mm more ventralward and dorsalward which lengthened (hold-long) and shortened (hold-short) the lumbar muscles. Following the conditioning hold positions, L(6) was returned to the intermediate position. Muscle spindle discharge at this position and during a lengthening movement was compared between hold-intermediate and hold-short conditionings and between hold-intermediate and hold-short conditionings. We found that regardless of conditioning magnitude, the seven shortening magnitudes similarly increased muscle spindle responsiveness to both vertebral position and movement. In contrast, the seven lengthening magnitudes produced a graded decrease in responsiveness to both position and movement. The decrease to position became maximal following conditioning magnitudes of ∼0.75 mm. The decrease to movement did not reach a maximum even with conditioning magnitudes of ∼1.55 mm. The data suggest that the fidelity of proprioceptive information from muscle spindles in the low back is influenced by small changes in the previous length history of lumbar muscles.

Acute repetitive lumbar syndrome: a multi-component insight into the disorder

PURPOSE

Repetitive Lumbar Injury (RLI) is common in individuals engaged in long term performance of repetitive occupational/sports activities with the spine. The triggering source of the disorder, tissues involved in the failure and biomechanical, neuromuscular, and biological processes active in the initiation and development of the disorder, are not known. The purpose is, therefore, to test, using in-vivo feline model and healthy human subjects, the hypothesis that RLI due to prolonged exposure to repetitive lumbar flexion-extension is triggered by an acute inflammation in the viscoelastic tissues and is characterized by lingering residual creep, pronounced changes in neuromuscular control and transient changes in lumbar stability. This report, therefore, is a summary of a lengthy research program consisting of multiple projects.

METHODS

A series of experimental data was obtained from in-vivo feline groups and normal humans subjected to prolonged cyclic lumbar flexion-extension at high and low loads, high and low velocities, few and many repetitions, as well as short and long in-between rest periods, while recording lumbar displacement and multifidi EMG. Neutrophil and cytokines expression analysis were performed on the dissected feline supraspinous ligaments before loading (control) and 7 h post-loading. A comprehensive, time based model was designed to represent the creep, motor control, tissue biology and stability derived from the experimental data.

RESULTS

Prolonged cyclic loading induced creep in the spine, reduced muscular activity, triggered spasms and reduced stability followed, several hours later, by acute inflammation/tissue degradation, muscular hyperexcitability and hyperstability. Fast movement, high loads, many repetitions and short rest periods, triggered the full disorder, whereas low velocities, low loads, long rest and few repetitions, triggered only minor but statistically significant pro-inflammatory tissue degradation and significantly reduced stability.

CONCLUSION

Viscoelastic tissue failure via inflammation is the source of RLI and is also the process which governs the mechanical and neuromuscular characteristic symptoms of the disorder. The experimental data validates the hypothesis and provides insights into the development of potential treatments and prevention.