More than movement: the proprioceptive system as a new regulator of musculoskeletal biology

In Myotonic Dystrophy Type 1 Head Repositioning Errors Suggest Impaired Cervical Proprioception

Background: Myotonic dystrophy type 1 (DM1) is a rare multisystemic genetic disorder with motor hallmarks of myotonia, muscle weakness and wasting. DM1 patients have an increased risk of falling of multifactorial origin, and proprioceptive and vestibular deficits can contribute to this risk. Abnormalities of muscle spindles in DM1 have been known for years. This observational cross-sectional study was based on the hypothesis of impaired cervical proprioception caused by alterations in the neck spindles. Methods: Head position sense was measured in 16 DM1 patients and 16 age- and gender-matched controls. A head-to-target repositioning test was requested from blindfolded participants. Their head was passively rotated approximately 30° leftward or rightward and flexed or extended approximately 25°. Participants had to replicate the imposed positions. An optoelectronic system was adopted to measure the angular differences between the reproduced and the imposed positions (joint position error, JPE, °) concerning the intended (sagittal, horizontal) and unintended (including the frontal) planar projections. In DM1 patients, JPEs were correlated with clinical and balance measures. Static balance in DM1 patients was assessed through dynamic posturography. Results: The accuracy and precision of head repositioning in the intended sagittal and horizontal error components did not differ between DM1 and controls. On the contrary, DM1 patients showed unintended side-bending to the left and the right: the mean [95%CI] of frontal JPE was -1.29° [-1.99°, -0.60°] for left rotation and 0.98° [0.28°, 1.67°] for right rotation. The frontal JPE of controls did not differ significantly from 0° (left rotation: 0.17° [-0.53°, 0.87°]; right rotation: -0.22° [-0.91°, 0.48°]). Frontal JPE differed between left and right rotation trials (p < 0.001) only in DM1 patients. No correlation was found between JPEs and measures from dynamic posturography and clinical scales. Conclusions: Lateral head bending associated with head rotation may reflect a latent impairment of neck proprioception in DM1 patients.

Impact of Glycemic Control on Shoulder Proprioception in Type 2 Diabetes Mellitus: Mediating the Connection - Insights from a Cross-Sectional Analysis

Introduction

Shoulder proprioception is vital and this cross-sectional study investigated the association between glycemic control and shoulder joint proprioception in Type 2 Diabetes Mellitus (T2DM).

Methods

A total of 120 participants, including 60 with T2DM and 60 healthy individuals, were assessed for shoulder joint position sense (JPS) using a digital inclinometer. The T2DM group exhibited significantly greater mean shoulder joint position errors in flexion (4.32° vs 2.15°), abduction, medial rotation, and lateral rotation compared to the healthy group (p < 0.001).

Results

The study found significantly greater shoulder joint position errors in the T2DM group compared to the healthy group, highlighting notable proprioceptive deficits in individuals with T2DM. Additionally, a significant positive correlation was found between HbA1c levels and shoulder joint position errors in the T2DM group, suggesting a link between long-term glycemic control and proprioceptive accuracy.

Discussion

The significant positive correlation between HbA1c levels and shoulder joint position errors suggests that poor glycemic control is associated with impaired proprioception in T2DM patients. This underscores the need for comprehensive management strategies to mitigate proprioceptive deficits and improve the quality of life in individuals with T2DM.

Kinematics but not kinetics alterations to single-leg drop jump movements following a subject-tailored fatiguing protocol suggest an increased risk of ACL injury

Introduction

Neuromuscular fatigue causes a transient reduction of muscle force, and alters the mechanisms of motor control. Whether these alterations increase the risk of anterior cruciate ligament (ACL) injury is still debated. Here we compare the biomechanics of single-leg drop jumps before and after the execution of a fatiguing exercise, evaluating whether this exercise causes biomechanical alterations typically associated with an increased risk of ACL lesion. The intensity of the fatiguing protocol was tailored to the aerobic capacity of each participant, minimizing potential differential effects due to inter-individual variability in fitness.

Methods

Twenty-four healthy male volunteers performed single leg drop jumps, before and after a single-set fatiguing session on a cycle ergometer until exhaustion (cadence: 65-70 revolutions per minute). For each participant, the intensity of the fatiguing exercise was set to 110% of the power achieved at their anaerobic threshold, previously identified by means of a cardiopulmonary exercise test. Joint angles and moments, as well as ground reaction forces (GRF) before and after the fatiguing exercise were compared for both the dominant and the non-dominant leg.

Results

Following the fatiguing exercise, the hip joint was more extended (landing: Δ=-2.17°, p = 0.005; propulsion: Δ=-1.83°, p = 0.032) and more abducted (landing: Δ=-0.72°, p = 0.01; propulsion: Δ=-1.12°, p = 0.009). Similarly, the knee joint was more extended at landing (non-dominant leg: Δ=-2.67°, p < 0.001; dominant: Δ=-1.4°, p = 0.023), and more abducted at propulsion (both legs: Δ=-0.99°, p < 0.001) and stabilization (both legs: Δ=-1.71°, p < 0.001) hence increasing knee valgus. Fatigue also caused a significant reduction of vertical GRF upon landing (Δ=-0.21 N/kg, p = 0.003), but not during propulsion. Fatigue did not affect joint moments significantly.

Conclusion

The increased hip and knee extension, as well as the increased knee abduction we observed after the execution of the fatiguing exercise have been previously identified as risk factors for ACL injury. These results therefore suggest an increased risk of ACL injury after the execution of the participant-tailored fatiguing protocol proposed here. However, the reduced vertical GRF upon landing and the preservation of joint moments are intriguing, as they may suggest the adoption of protective strategies in the fatigued condition to be evaluated in future studied.

The mechanosensitive ion channel ASIC2 mediates both proprioceptive sensing and spinal alignment

By translating mechanical forces into molecular signals, proprioceptive neurons provide the CNS with information on muscle length and tension, which is necessary to control posture and movement. However, the identities of the molecular players that mediate proprioceptive sensing are largely unknown. Here, we confirm the expression of the mechanosensitive ion channel ASIC2 in proprioceptive sensory neurons. By combining in vivo proprioception-related functional tests with ex vivo electrophysiological analyses of muscle spindles, we showed that mice lacking Asic2 display impairments in muscle spindle responses to stretch and motor coordination tasks. Finally, analysis of skeletons of Asic2 loss-of-function mice revealed a specific effect on spinal alignment. Overall, we identify ASIC2 as a key component in proprioceptive sensing and a regulator of spine alignment.

Inhibition of knee joint sensory afferents alters covariation across strides between quadriceps muscles during locomotion

Sport-related injuries to articular structures often alter the sensory information conveyed by joint structures to the nervous system. However, the role of joint sensory afferents in motor control is still unclear. Here, we evaluate the role of knee joint sensory afferents in the control of quadriceps muscles, hypothesizing that such sensory information modulates control strategies that limit patellofemoreal joint loading. We compared locomotor kinematics and muscle activity before and after inhibition of knee sensory afferents by injection of lidocaine into the knee capsule of rats. We evaluated whether this inhibition reduced the strength of correlation between the activity of vastus medialis (VM) and vastus lateralis (VL) both across strides and within each stride, coordination patterns that limit net mediolateral patellofemoral forces. We also evaluated whether this inhibition altered correlations among the other quadriceps muscle activity, the time-profiles of individual EMG envelopes, or movement kinematics. Neither the EMG envelopes nor limb kinematics was affected by the inhibition of knee sensory afferents. This perturbation also did not affect the correlations between VM and VL, suggesting that the regulation of patellofemoral joint loading is mediated by different mechanisms. However, inhibition of knee sensory afferents caused a significant reduction in the correlation between vastus intermedius (VI) and both VM and VL across, but not within, strides. Knee joint sensory afferents may therefore modulate the coordination between the vasti muscles but only at coarse time scales. Injuries compromising joint afferents might result in altered muscle coordination, potentially leading to persistent internal joint stresses and strains.NEW & NOTEWORTHY Sensory afferents originating from knee joint receptors provide the nervous system with information about the internal state of the joint. In this study, we show that these sensory signals are used to modulate the covariations among the activity of a subset of vasti muscles across strides of locomotion. Sport-related injuries that damage joint receptors may therefore compromise these mechanisms of muscle coordination, potentially leading to persistent internal joint stresses and strains.

Kinesthetic Coordination Abilities in 6-Year-Old Children: School Quintile, Gender, and Hand Dominance Differences

Proprioceptive kinaesthetic control underpins motor movements of developing children and can be influenced by several factors. The main aim of this study was to establish proprioceptive kinaesthetic coordination differences in six-year-olds from different school quintiles, of different genders, and with different handedness. A total of 193 six-year-olds from 10 schools of different quintiles in the Motheo District, Mangaung, were included, of which 97 (50.3%) were boys and 96 (49.7%) were girls. A quantitative cross-sectional study design was followed to determine proprioceptive kinaesthetic coordination differences. Right-handed participants performed significantly better than left-handed participants in the Finger-to-Nose task (p = 0.0125) when moving and positioning their dominant arm and hand. When using their dominant arm, significant differences in the shoulder-level-arm-raise (p = 0.0288) favoured boys. Girls showed superior execution of the force perception task (p = 0.0322). In conclusion, significant proprioceptive kinaesthetic coordination differences in six-year-olds were mainly not evident. Future work should explore proprioceptive kinaesthetic coordination differences in children of other ages and determine the practical implications of identified differences.

Molecular characterization of the intact mouse muscle spindle using a multi-omics approach

The proprioceptive system is essential for the control of coordinated movement, posture, and skeletal integrity. The sense of proprioception is produced in the brain using peripheral sensory input from receptors such as the muscle spindle, which detects changes in the length of skeletal muscles. Despite its importance, the molecular composition of the muscle spindle is largely unknown. In this study, we generated comprehensive transcriptomic and proteomic datasets of the entire muscle spindle isolated from the murine deep masseter muscle. We then associated differentially expressed genes with the various tissues composing the spindle using bioinformatic analysis. Immunostaining verified these predictions, thus establishing new markers for the different spindle tissues. Utilizing these markers, we identified the differentiation stages the spindle capsule cells undergo during development. Together, these findings provide comprehensive molecular characterization of the intact spindle as well as new tools to study its development and function in health and disease.

Proprioceptive based training or modified constraint-induced movement therapy on upper extremity motor functions in chronic stroke patients: A randomized controlled study

BACKGROUND: The Modified Constraint-Induced Movement Therapy (mCIMT) method is a unilateral training that respectively avoids and activates less affected and affected sides of upper extremities; however, the selected options are not typically ideal. Proprioceptive based training (PT) includes bilateral training methods and influencing proprioceptive receptors. OBJECTIVE: The primary purpose was to determine if conventional therapy and PT or conventional therapy and mCIMT therapy show similar improvement in patients with chronic stroke. The secondary purpose was to investigate the effectiveness of conventional therapy and PT or mCIMT therapy in patients with chronic stroke and to compare which of the two interventions is more effective. METHODS: Forty patients with chronic stroke were randomly allocated to only conventional therapy (PTR, n = 14), conventional therapy plus proprioception training (PTR-PT, n = 13), and mCIMT (PTR-mCIMT, n = 13) groups. Evaluations were assessed before and 6 weeks after treatment. RESULTS: Intragroup evaluations revealeda significant improvement in the all scores in the PTR-PT and PTR-mCMIT groups (p = 0.006 < 0.001). Intergroup comparisons demonstrated that the PTR-mCIMT group had a significant improvement in spasticity and motor function scores compared to the PTR (p < 0.001) and the PTR-PT groups (p = 0.006–0.015). CONCLUSIONS: PT and mCMIT applied in addition to conventional therapy in patients with chronic stroke were more effective than only conventional therapy. Additionally, mCMIT showed greater improvement in spasticity and motor function scales than PT.

Osteoporosis in Light of a New Mechanism Theory of Delayed Onset Muscle Soreness and Non-Contact Anterior Cruciate Ligament Injury

Osteoporosis is a disorder, with a largely unknown pathomechanism, that is often marked as a “silent thief”, because it usually only becomes undisguised when fractures occur. This implies that the pathological damage occurs earlier than the sensation of pain. The current authors put forward a non-contact injury model in which the chronic overloading of an earlier autologously microinjured Piezo2 ion channel of the spinal proprioceptor terminals could lead the way to re-injury and earlier aging in a dose-limiting and threshold-driven way. As a result, the aging process could eventually lead the way to the metabolic imbalance of primary osteoporosis in a quad-phasic non-contact injury pathway. Furthermore, it is emphasised that delayed onset muscle soreness, non-contact anterior cruciate injury and osteoporosis could have the same initiating proprioceptive non-contact Piezo2 channelopathy, at different locations, however, with different environmental risk factors and a different genetic predisposition, therefore producing different outcomes longitudinally. The current injury model does not intend to challenge any running pathogenic theories or findings, but rather to highlight a principal injury mechanism.

Reciprocal interactions between transforming growth factor beta signaling and collagens: Insights from Caenorhabditis elegans

Studies in genetically tractable organisms such as the nematode Caenorhabditis elegans have led to pioneering insights into conserved developmental regulatory mechanisms. For example, Smad signal transducers for the transforming growth factor beta (TGF-β) superfamily were first identified in C. elegans and in the fruit fly Drosophila. Recent studies of TGF-β signaling and the extracellular matrix (ECM) in C. elegans have forged unexpected links between signaling and the ECM, yielding novel insights into the reciprocal interactions that occur across tissues and spatial scales, and potentially providing new opportunities for the study of biomechanical regulation of gene expression.

The contemporary model of vertebral column joint dysfunction and impact of high-velocity, low-amplitude controlled vertebral thrusts on neuromuscular function

Purpose

There is growing evidence that vertebral column function and dysfunction play a vital role in neuromuscular control. This invited review summarises the evidence about how vertebral column dysfunction, known as a central segmental motor control (CSMC) problem, alters neuromuscular function and how spinal adjustments (high-velocity, low-amplitude or HVLA thrusts directed at a CSMC problem) and spinal manipulation (HVLA thrusts directed at segments of the vertebral column that may not have clinical indicators of a CSMC problem) alters neuromuscular function.

Methods

The current review elucidates the peripheral mechanisms by which CSMC problems, the spinal adjustment or spinal manipulation alter the afferent input from the paravertebral tissues. It summarises the contemporary model that provides a biologically plausible explanation for CSMC problems, the manipulable spinal lesion. This review also summarises the contemporary, biologically plausible understanding about how spinal adjustments enable more efficient production of muscular force. The evidence showing how spinal dysfunction, spinal manipulation and spinal adjustments alter central multimodal integration and motor control centres will be covered in a second invited review.

Results

Many studies have shown spinal adjustments increase voluntary force and prevent fatigue, which mainly occurs due to altered supraspinal excitability and multimodal integration. The literature suggests physical injury, pain, inflammation, and acute or chronic physiological or psychological stress can alter the vertebral column’s central neural motor control, leading to a CSMC problem. The many gaps in the literature have been identified, along with suggestions for future studies.

Conclusion

Spinal adjustments of CSMC problems impact motor control in a variety of ways. These include increasing muscle force and preventing fatigue. These changes in neuromuscular function most likely occur due to changes in supraspinal excitability. The current contemporary model of the CSMC problem, and our understanding of the mechanisms of spinal adjustments, provide a biologically plausible explanation for how the vertebral column’s central neural motor control can dysfunction, can lead to a self-perpetuating central segmental motor control problem, and how HVLA spinal adjustments can improve neuromuscular function.