Test-retest reliability and construct validity of trunk extensor muscle force modulation accuracy.

Low back pain is associated with changes in trunk muscle structure and function and motor control impairments. Voluntary force modulation (FM) of trunk muscles is a unique and under-investigated motor control characteristic. One of the reasons for this paucity of evidence is the lack of exploration and publication on the reliability and validity of trunk FM protocols. The purpose of this study was to determine the within- and between-day test-retest reliability and construct validity for trunk extensor muscle FM. Twenty-nine healthy participants were tested under three FM conditions with different modulation rates. Testing was performed on a custom-built apparatus designed for trunk isometric force testing. FM accuracy relative to a fluctuating target force (20-50%MVF) was quantified using the root mean square error of the participant's generated force relative to the target force. Reliability and precision of measurement were assessed using the Intraclass Correlation Coefficient (ICC), standard error of measurement (SEM), minimal detectable difference (MDD95), and Bland-Altman plots. In a subset of participants, we collected surface electromyography of trunk and hip muscles. We used non-negative matrix factorization (NNMF) to identify the underlying motor control strategies. Within- and between-day test-retest reliability was excellent for FM accuracy across the three conditions (ICC range: 0.865 to 0.979). SEM values ranged 0.9-1.8 Newtons(N) and MDD95 ranged from 2.4-4.9N. Conditions with faster rates of FM had higher ICCs. NNMF analysis revealed two muscle synergies that were consistent across participants and conditions. These synergies demonstrate that the muscles primarily involved in this FM task were indeed the trunk extensor muscles. This protocol can consistently measure FM accuracy within and between testing sessions. Trunk extensor FM, as measured by this protocol, is not specific to any trunk muscle group but is the result of modulation by all the trunk extensor muscles.

Mind-Body Exercise Performed by Physical Therapists for Reducing Pain and Disability in Low Back Pain: A Systematic Review With Meta-analysis.

OBJECTIVE: To assess the effectiveness of mind-body (MB) exercise interventions provided by physical therapists for reducing pain and disability in people with low back pain (LBP). DATA SOURCES: MEDLINE, Embase, CINAHL, and the Cochrane Library were searched for articles published in English between December 2010 and June 2020. STUDY SELECTION: Randomized controlled trials evaluating the effects of Pilates, yoga, and tai chi interventions performed by physical therapists on pain or disability outcomes in adults with musculoskeletal LBP were included. DATA EXTRACTION: Data were extracted by 2 independent reviewers. Quality of evidence and risk of bias were assessed using the Grading of Recommendations Assessment, Development, and Evaluation framework and Cochrane risk of bias tools, respectively. DATA SYNTHESIS: 21,230 exercise trials were identified; 161 progressed to full-text review. Eight trials, 7 reporting on Pilates and 1 reporting on yoga, were included. Short-term outcomes for pain (SMD: -0.93; 95% confidence interval [CI]: -1.65 to -0.021) and disability (SMD: -0.74 95% CI: -1.36 to -0.012) indicated MB exercise was more effective than control intervention. Tests for subgroup differences between studies with exercise vs non-exercise control groups revealed a moderating effect on short-term outcomes where larger effects were observed in studies with non-exercise comparators. Long-term outcomes for pain (SMD: -0.60; 95% CI:-1.43 to 0.23) and disability (SMD: -1.05; 95% CI:-3.51 to 1.41) suggested that MB exercise is not more effective than control interventions for pain or disability. Quality of the evidence ranged from very low to low. CONCLUSIONS: Physical therapist-delivered MB exercise interventions, which overwhelmingly consisted of Pilates, were more effective than control in the short and long-term for pain and in the short-term for disability, with differences in the short-term effects lessened when compared with an active intervention. Pilates interventions delivered by physical therapists represent a viable tool for the clinical management of chronic LBP.

The Neurophysiological Impact of Experimentally-Induced Pain on Direct Muscle Spindle Afferent Response: A Scoping Review.

Background: Musculoskeletal pain disorders are among the leading causes of years lived with disability worldwide representing a significant burden to society. Studies investigating a "nociceptive-fusimotor" relationship using experimentally-induced pain/noxious stimuli and muscle spindle afferent (MSA) response have been published over several decades. The purpose of this scoping review was to systematically identify and summarize research findings related to the impact of experimentally-induced pain or noxious stimulation on direct MSA discharge/response. Methods: PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane and Embase were searched from database inception to August 2020. Eligible studies were: (a) published in English; (b) clinical or pre-clinical studies; (c) original data studies; (d) included the investigation of MSA response to experimentally-induced pain or noxious stimulation; (e) included quantification of at least one direct physiological measure associated with MSA activity/response. Two-phase screening procedures were conducted by a pair of independent reviewers and data extracted from eligible studies. Results: The literature search resulted in 195 articles of which 23 met inclusion criteria. Six studies (26%) were classified as clinical and 17 (74%) as pre-clinical. Two clinical studies investigated the effects of sacral dermatome pin-pricking on MSA response, while the remaining 4 studies investigated the effects of tonic muscle and/or skin pain induced by injection/infusion of hypertonic saline into the tibialis anterior muscle or subdermal tissues. In pre-clinical studies, muscle pain was induced by injection of noxious substances or the surgical removal of the meniscus at the knee joint. Conclusion: Clinical studies in awake humans reported that experimentally-induced pain did not affect, or else slightly decreased MSA spontaneous discharge and/or response during weak dorsiflexor muscle contraction, thus failing to support an excitatory nociceptive-fusimotor relationship. However, a majority of pre-clinical studies indicated that ipsilateral and contralateral muscle injection of noxious substances altered MSA resting discharge and/or response to stretch predominately through static fusimotor reflex mechanisms. Methodological differences (use of anesthesia, stretch methodology, etc.) may ultimately be responsible for the discrepancies between clinical and pre-clinical findings. Additional investigative efforts are needed to reconcile these discrepancies and to clearly establish or refute the existence of nociceptive-fusimotor relationship in muscular pain.