Practicable performance-based outcome measures of trunk muscle strength and their measurement properties: A systematic review and narrative synthesis

Introduction

The evaluation of muscle strength is frequently used as part of the physical examination process, with decreased trunk muscle strength reported in individuals with spinal disorders (e.g., low back pain). Access to practicable performance-based outcome measures (PBOM) to monitor patients’ progress in spinal rehabilitation is essential. Knowledge of the psychometric properties of the available practicable PBOM for trunk strength evaluation is therefore needed to inform practitioners and further research.

Objective

To synthesise evidence on the measurement properties of practicable measures of trunk muscle strength in adults with and without musculoskeletal pain.

Methods

Following a published and registered protocol [PROSPERO CRD42020167464], databases were searched from the database inception date up to 30th of June 2021. Citations and grey literature were also searched. Eligibility criteria comprised: 1) studies which examined the psychometric properties of the trunk strength outcome measures, 2) included adults ≥ 18 years, either asymptomatic or with spinal musculoskeletal pain. Non-English language studies were excluded. Two independent reviewers evaluated the quality and synthesized the data from included studies according to the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN) checklist. The overall quality of evidence was evaluated using a modified Grading of Recommendations Assessment Development and Evaluation (GRADE).

Results

From 34 included studies, 15 different PBOMs were identified that have been investigated for reliability and validity, none evaluated responsiveness. In asymptomatic individuals, high quality evidence supports intra-rater reliability of digital-loading cells and moderate quality evidence supports the criterion validity of the hand-held dynamometer. Very low quality evidence exists for the reliability and validity estimates of testing tools among individuals with spinal pain.

Conclusions

Findings underpin a cautious recommendation for the use of practicable PROMs to evaluate muscle strength in individuals with spinal pain in clinical practice due to the level of evidence and the heterogeneity of the protocols used. Further high quality research to explore the psychometric properties of the practicable PBOMs with detailed methodology is now needed.

Core Muscle Activation With Foam Rolling and Static Planks

The objective of this study was to compare the activation of the core (trunk) musculature during quadriceps and hamstrings foam rolling (FR) vs. prone and supine/reverse static planks to determine if FR is a viable means of training the core musculature. Using a randomized allocation, nine recreationally trained, young adults (18-26 years) performed two sets each of quadriceps and hamstrings FR as well as supine/reverse and prone static planks for 30-s each with 1-min rest between sets and 5-min rest between exercises. Electromyographic (EMG) activity of the lower abdominals (LA), external obliques (EO), lumbosacral erector spinae (LSES), upper lumbar erector spinae (ULES) muscle groups were normalized to a maximum voluntary contraction and analyzed. Quadriceps FR exhibited a very large magnitude greater LA activity compared to reverse plank (p = 0.033, d = 4.42) and hamstrings FR (p = 0.020, d = 3.49), respectively. The prone plank demonstrated very large magnitude higher EO EMG activity compared to reverse plank (p = 0.001, d = 9.17), hamstrings FR (p = 0.002, d = 8.14), and quadriceps FR (p = 0.011, d = 5.97). Reverse plank (p = 0.003, d = 12.06), and quadriceps FR (p = 0.002, d = 7.84) induced greater ULES activity compared to the prone plank and hamstrings FR, respectively. Reverse plank also exhibited very large magnitude higher LSES activity compared to the prone plank (p < 0.001, d = 7.68), hamstrings FR (p = 0.002, d = 4.11), and quadriceps FR (p = 0.005, d = 2.34), respectively. In conclusion, whereas reverse plank was the most effective activator of dorsal core muscles, quadriceps FR may also be a time efficient alternative exercise to activate back (ventral core) muscles. The prone plank is effective for ventral core muscles activation.

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.

The relationship between balance performance, lumbar extension strength, trunk extension endurance, and pain in participants with chronic low back pain, and those without

BACKGROUND

Chronic low back pain is associated with lumbar extensor deconditioning. This may contribute to decreased neuromuscular control and balance. However, balance is also influenced by the hip musculature. Thus, the purpose of this study was to examine balance in both asymptomatic participants and those with chronic low back pain, and to examine the relationships among balance, lumbar extension strength, trunk extension endurance, and pain.

METHODS

Forty three asymptomatic participants and 21 participants with non-specific chronic low back pain underwent balance testing using the Star Excursion Balance Test, lumbar extension strength, trunk extension endurance, and pain using a visual analogue scale.

FINDINGS

Significant correlations were found between lumbar extension strength and Star Excursion Balance Test scores in the chronic low back pain group (r = 0.439-0.615) and in the asymptomatic group (r = 0.309-0.411). Correlations in the chronic low back pain group were consistently found in posterior directions. Lumbar extension strength explained ~19.3% to ~37.8% of the variance in Star Excursion Balance Test scores for the chronic low back pain group and ~9.5% to ~16.9% for the asymptomatic group.

INTERPRETATION

These results suggest that the lumbar extensors may be an important factor in determining the motor control dysfunctions, such as limited balance, that arise in chronic low back pain. As such, specific strengthening of this musculature may be an approach to aid in reversing these dysfunctions.

Association between spectral characteristics of paraspinal muscles and functional disability in patients with low back pain: a cohort study

OBJECTIVES

Characteristics of muscle activity, represented by surface electromyography (EMG), have revealed differences between patients with low back pain (LBP) and healthy adults; how they relate to functional and clinical parameters remains unclear. The purpose of the current study was to examine the correlation between frequency characteristics of EMG (analysed using continuous wavelet transform (CWT) analysis) and patients' self-rated score of disability.

DESIGN AND SETTING

This is a case-control study with 15 patients with mechanical LBP without radicular symptoms. Patients were recruited from the orthopaedic clinic at Charing Cross Hospital. Ten healthy adults were recruited from the staff working in the hospital and associated university. Patients completed the Roland-Morris Disability Questionnaire (RMDQ) and bilateral EMG activity was obtained from erector spinae at vertebral levels L4 and T12. Subjects performed three brief maximal voluntary isometric contractions (MVICs) of the back extensors and the torque was measured using a dynamometer. CWT was applied to the EMG signals of each muscle in a 200 ms window centred around the peak torque obtained during the MVICs. The ratio (low/high frequencies) of the energy, the peak power and the frequency of the peak power were calculated for each recording site, averaged and correlated with the individual's RMDQ score.

RESULTS

Patients had lower peak power (T12 and L4) and lower frequency of the peak power (at T12) than the healthy adults. Additionally, RMDQ positively correlated to the average ratio of energy at T12 (r=0.63; p=0.012), that is, greater self-rated disability corresponded to a dominant distribution of energy in the lower frequencies.

CONCLUSION

The current findings reveal alterations in EMG profile and its association with self-related back pain disability, suggesting that spectral characteristics of EMG reflect muscle function.

Impact of NFL PLAY 60 Programming on Elementary School Children's Body Mass Index and Aerobic Capacity: The NFL PLAY 60 FitnessGram Partnership Project

BACKGROUND

We examined the impact of the Fuel Up to Play 60 (FUTP60) program on children's body mass index (BMI) and aerobic capacity (AC).

METHODS

Participation in the FUTP60 and both BMI and AC profiles were collected through the NFL PLAY 60 FitnessGram Partnership Project involving over 100 schools from 22 US states. We specifically examined the distributions of BMI and AC among participating versus nonparticipating schools in the 2012-2013 school year. Hierarchical linear models tested the impact of participation and availability of additional funding for program implementation on the proportions of youth meeting FitnessGram health-related fitness standards (ie, Needs Improvement-Health Risk [NIHR] and Healthy Fitness Zone [HFZ] categories).

RESULTS

After 1 year implementing the program, participating schools had lower proportions of boys (-4.1 ± 2.0%, p = .04) and girls (-4.5 ± 2.0%, p = .03) in the NIHR for BMI, and lower proportion of girls (-9.7 ± 4.0%, p = .02) in the NIHR for AC. There were no differences in the distributions for the HFZ and the availability of additional funding did not alter the relationships (p > .05).

CONCLUSIONS

This study provides preliminary evidence that participation in the FUTP60 is associated with improved profiles of health-related fitness.

Precision based guidelines for sub-maximal normalisation task selection for trunk extensor EMG

AIM

The object of this study was to quantify the contribution of sub-maximal normalisation to the overall variance of exposure parameters describing erector spinae (ES) activity, and to provide guidelines for task selection which minimize methodological variance.

METHODS

ES EMG was measured from three locations (T9, L1 and L5 levels) on fifteen men performing a manual materials handling task in the laboratory on three separate days. Four repeats of each of eleven sub-maximal normalisation tasks (eight static, three dynamic) were collected, work data were normalised to each task and repeat, and exposure parameters calculated. The unique contribution of normalisation to the overall variance was determined for each task and exposure parameter using variance component analyses. Normalisation tasks were scored according to their relative contributions to the overall variance and coefficients of variation.

RESULTS

A prone task, similar to the Biering-Sørensen test posture, was the most repeatable for all electrode locations and across all exposure parameters. Thoracic level normalisation typically showed poorer repeatability than lumbar normalisation.

DISCUSSION

To maximize measurement precision, we recommend that future ES EMG studies employing sub-maximal normalisation utilise said prone task. An alternate normalisation task specific to thoracic level ES muscles may be warranted.

A biomechanical and subjective comparison of two powered ambulance cots

This study investigated biomechanical effects of different leg folding/unfolding mechanisms used for loading/unloading two powered cots (Cots A and B) into and from a simulated ambulance. Sixteen experienced emergency medical service (EMS) workers loaded and unloaded cots with weights of 45, 68 and 91 kg placed on the cots to simulate patients. Peak back and shoulder/arm muscle activity was reduced 52-87% when using Cot A in comparison to Cot B. Peak ground reaction force (PGRF) was reduced by 74% with Cot A. Adding weight resulted in increased muscle activity and PGRF when using Cot B, but had little effect when using Cot A. Task time was longer with Cot A, though was not perceived unfavourably by participants. This study confirmed that it is possible to substantially reduce physical stress imposed on EMS workers when loading and unloading a cot to and from an ambulance through improvements in cot design.

PRACTITIONER SUMMARY

This study compared two powered ambulance cots, one that lifts/lowers the front and rear wheels independently and one that lifts/lowers the four wheels simultaneously during ambulance loading and unloading. Measured muscle activity, ground reaction forces and operator perceptions support using cot designs that lift/lower the front and rear wheels independently.

Breathing Techniques Affect Female but Not Male Hip Flexion Range of Motion

Two protocols were undertaken to help clarify the effects of breathing techniques on hamstrings (hip flexion) range of motion (ROM). The protocols examined effects of breathing conditions on ROM and trunk muscle activity. Protocol 1: Thirty recreationally active participants (15 male, 15 female, 20-25 years) were monitored for changes in single-leg raise (SLR) ROM with 7 breathing conditions before or during a passive supine SLR stretch. Breathing conditions included prestretch inhale, prestretch exhale, inhale-during stretch, exhale-during stretch, neutral, hyperventilation, and hypoventilation before stretch. Protocol 2: Eighteen recreationally active participants (9 male, 9 female, 20-25 years) were monitored for electromyographic (EMG) activity of the rectus abdominus, external obliques, lower abdominal stabilizers, and lower erector spinae while performing the 7 breathing conditions before or during a passive SLR stretch. Control exhibited less ROM (p = 0.008) than the prestretch inhale (7.7%), inhale-during stretch (10.9%), and hypoventilation (11.2%) conditions with females. Protocol 3: Greater overall muscle activity in the prestretch exhale condition was found compared with inhale-during stretch (43.1%↓; p = 0.029) and hypoventilation (51.2%↓; p = 0.049) conditions. As the inhale-during stretch and hypoventilation conditions produced the lowest levels of muscle activity for both sexes and the highest ROM for the females, it can be assumed that both mechanical and neural factors affect female SLR ROM. Lesser male ROM might be attributed to anatomical differences such as greater joint stiffness. The breathing techniques may have affected intra-abdominal pressure, trunk muscle cocontractions, and sympathetic neural activity to enhance female ROM.

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.

Trunk extensor fatigue decreases jump height similarly under stable and unstable conditions with experienced jumpers

PURPOSE

The purpose of this study was to investigate the effects of back extensor fatigue on performance measures and electromyographic (EMG) activity of leg and trunk muscles during jumping on stable and unstable surfaces.

METHODS

Before and after a modified Biering-Sorensen fatigue protocol for the back extensors, countermovement (CMJ) and lateral jumps (LJ) were performed on a force plate under stable and unstable (balance pad on the force plate) conditions. Performance measures for LJ (contact time) and CMJ height and leg and trunk muscles EMG activity were tested in 14 male experienced jumpers during 2 time intervals for CMJ (braking phase, push-off phase) and 5 intervals for LJ (-30 to 0, 0-30, 30-60, 60-90, and 90-120 ms) in non-fatigued and fatigued conditions.

RESULTS

A significant main effect of test (fatigue) (p = 0.007, f = 0.57) was observed for CMJ height. EMG analysis showed a significant fatigue-induced decrease in biceps femoris and gastrocnemius activity with CMJ (p = 0.008, f = 0.58 andp = 0.04, f = 0.422, respectively). LJ contact time was not affected by fatigue or surface interaction. EMG activity was significantly lower in the tibialis anterior with LJ following fatigue (p = 0.05, f = 0.405). A test x surface (p = 0.04, f = 0.438) interaction revealed that the non-fatigued unstable CMJ gastrocnemius EMG activity was lower than the non-fatigued stable condition during the onset-of-force phase.

CONCLUSION

The findings revealed that fatiguing the trunk negatively impacts CMJ height and muscle activity during the performance of CMJs. However, skilled jumpers are not additionally affected by a moderately unstable surface as compared to a stable surface.

A reappraisal of the deconditioning hypothesis in low back pain: review of evidence from a triumvirate of research methods on specific lumbar extensor deconditioning

OBJECTIVE

'Disuse' and 'Deconditioning' in relation to low back pain (LBP) are terms often used interchangeably. Discussions of 'disuse' refer to general physical inactivity, which evidence suggests does not differ between symptomatic and asymptomatic persons. 'Deconditioning' refers to a decrease in function, commonly both cardiovascular/aerobic fitness and muscular strength/endurance, again noting little difference. However, examination of decreased function relating specifically to lumbar extensor musculature deconditioning has yet to be examined, corroborating all possible methods. Thus, this review attempts to reappraise the deconditioning hypothesis in LBP, specifically considering lumbar extensor deconditioning.

METHODS

A literature review was conducted examining both cross-sectional and prospective data on specific lumbar extensor deconditioning and LBP. A narrative approach and 'snowballing' style literature search was used involving initial use of PubMed and Google Scholar databases searching up to December 2012. Included were studies utilizing the following three research methods, allowing specific induction of the role of such deconditioning; (1) strength/endurance testing of the isolated lumbar extensor musculature, (2) imaging and histochemical examination of the lumbar extensor musculature, and (3) fatigue testing of the lumbar extensor musculature using electromyography.

RESULTS/FINDINGS

Despite issues interpreting individual studies due to methods, the majority of evidence suggests LBP is associated with decreased strength/endurance, atrophy, and excessive fatigability of the lumbar extensors. Prospective studies also suggest lumbar extensor deconditioning may be a common risk factor predicting acute low back injury and LBP.

CONCLUSIONS

The hypothesis of specific lumbar extensor deconditioning as being a causal factor in LBP is presently well supported. It is by no means the only causative factor and further research should more rigorously test this hypothesis addressing the methodological issues highlighted regarding previous studies. However, its role suggests specific exercise may be a worthwhile preventative and rehabilitative approach.

Temporal patterns of the trunk muscles remain altered in a low back-injured population despite subjective reports of recovery

OBJECTIVE

To compare temporal activation patterns from 24 abdominal and lumbar muscles between healthy subjects and those who reported recovery from recent low back injury (LBI).

DESIGN

Cross-sectional comparative study.

SETTING

University neuromuscular function laboratory.

PARTICIPANTS

Healthy adult volunteers (N=81; 30 LBI, 51 asymptomatic subjects).

INTERVENTIONS

Trunk muscle electromyographic activity was collected during 2 difficulty levels of a supine trunk stability test aimed at challenging lumbopelvic control.

MAIN OUTCOME MEASURES

Principal component (PC) analysis was applied to determine differences in temporal and/or amplitude electromyographic patterns between groups. Mixed-model analyses of variance were performed on PC scores that explained more than 89% of the variance (α=.05).

RESULTS

Four PCs explained 89% and 96% of the variance for the abdominal and back muscles, respectively, with both muscle groups having similar shapes in the first 3 PCs. Significant interactions or group main effects were found for all PC scores except PC4 for the back extensors. Overall activation amplitudes for both the abdominal and back muscles (PC1 scores) were significantly (P<.05) higher for the LBI group, with both abdominal and back muscles of the LBI group demonstrating an increased response to the leg-loading phase (PC2 scores) compared with the asymptomatic group. Differences were also found between groups in their preparatory activity (PC3 scores), with the LBI group having a higher early relative amplitude of abdominal and back extensor activity.

CONCLUSIONS

Despite perceived readiness to return to work and low pain scores, muscle activation patterns remained altered in this LBI group, including reduced synergistic coactivation and increased overall amplitudes as well as greater relative amplitude differences during specific phases of the movement. Electromyographic measures provide objective information to help guide therapy and may assist with determining the level of healing and return-to-work readiness after an LBI.

Test-retest reliability of v-wave responses in the soleus and gastrocnemius medialis

This study was designed to assess the reliability of the first volitional (V) wave, which can be used as a measure of efferent neural drive, while also reflecting reflex excitability. Ten subjects volunteered for one familiarization session followed by an experimental test session and an identical retest session spaced 3 to 8 days apart. V-waves were evoked in the tibial nerve during plantar flexion maximal voluntary isometric contractions (MVCs). Test-retest reliability was assessed using the intraclass correlation coefficient (ICC), along with standard error of measurement and 95% confidence intervals for the following variables: MVC force, surface electromyogram activity (EMG), and the peak-to-peak V-wave amplitude in soleus (SOL) and gastrocnemius medialis (GM). The superimposed M-wave (MSUP) accompanying V-wave stimulation was also obtained for normalization purposes. Substantial reliability was documented for V/MSUP in both SOL (ICC = 0.86) and GM (0.90), as well as for the non-normalized V-wave in SOL (0.92). Moderate reliability was displayed for the non-normalized V-wave response in GM (0.78). Substantial reliability was also established for EMG/MSUP (>0.82) and MVC force (0.98). This study provides novel evidence that V-wave responses can be consistently measured in the SOL and GM, thus advocating its continued use in future research.

Trunk muscle activation during moderate- and high-intensity running

Time constraints are cited as a barrier to regular exercise. If particular exercises can achieve multiple training functions, the number of exercises and the time needed to achieve a training goal may be decreased. It was the objective of this study to compare the extent of trunk muscle electromyographic (EMG) activity during running and callisthenic activities. EMG activity of the external obliques, lower abdominals (LA), upper lumbar erector spinae (ULES), and lumbosacral erector spinae (LSES) was monitored while triathletes and active nonrunners ran on a treadmill for 30 min at 60% and 80% of their maximum heart rate (HR) reserve, as well as during 30 repetitions of a partial curl-up and 3 min of a modified Biering-Sørensen back extension exercise. The mean root mean square (RMS) amplitude of the EMG signal was monitored over 10-s periods with measures normalized to a maximum voluntary contraction rotating curl-up (external obliques), hollowing exercise (LA), or back extension (ULES and LSES). A main effect for group was that triathletes had greater overall activation of the external obliques (p < 0.05), LA (p = 0.01), and LSES (p < 0.05) than did nonrunners. Main effects for exercise type showed that the external obliques had less EMG activity during 60% and 80% runs, respectively, than with the curl-ups (p = 0.001). The back extension exercise provided less ULES (p = 0.009) and LSES (p = 0.0001) EMG activity than the 60% and 80% runs, respectively. In conclusion, triathletes had greater trunk activation than nonrunners did while running, which could have contributed to their better performance. Back-stabilizing muscles can be activated more effectively with running than with a prolonged back extension activity. Running can be considered as an efficient, multifunctional exercise combining cardiovascular and trunk endurance benefits.

An inverted seated posture decreases elbow flexion force and muscle activation

The purpose of this study was to determine if discrepancies exist between upright and inverted seated positions in isometric maximal voluntary contraction (MVC) elbow flexor force, MVC force produced in the first 100 ms (F100), MVC rate of force development, electromyographic (EMG) activity of the biceps and triceps as well as heart rate and blood pressure. The results showed significantly (p < 0.01) higher MVC force (543.6 +/- 29.6 vs. 486.5 +/- 23.0 N), F100 (328.3 +/- 94.5 vs. 274.6 +/- 101.8 N), rate of force development (p = 0.003) (1,851.9 +/- 742.2 vs. 1,591.0 +/- 719.6 N s(-1)) and biceps brachii EMG activity (48%, p < 0.01) in the upright versus inverted condition. There were relatively greater co-contractions with the inverted position (p < 0.01) due to the lack of change in triceps' EMG and the substantial decrease in biceps' EMG. There were no significant changes in trunk EMG activity. With inversion, there were significant decreases in heart rate (16.8%), systolic (11.6%) and diastolic (12.1%) blood pressures (p < 0.0001). These results illustrate decrements in neuromuscular performance with an inverted seated posture which may be related to an altered sympathetic response.