The sensorimotor system, part I: the physiologic basis of functional joint stability

Objective: To define the nomenclature and physiologic mechanisms responsible for functional joint stability.Data Sources: Information was drawn from an extensive MEDLINE search of the scientific literature conducted in the areas of proprioception, neuromuscular control, and mechanisms of functional joint stability for the years 1970 through 1999. An emphasis was placed on defining pertinent nomenclature based on the original references.Data Synthesis: Afferent proprioceptive input is conveyed to all levels of the central nervous system. They serve fundamental roles in optimal motor control and sensorimotor control over functional joint stability.Conclusions/Applications: Sensorimotor control over the dynamic restraints is a complex process that involves components traditionally associated with motor control. Recognizing and understanding the complexities involved will facilitate the continued development and institution of management strategies based on scientific rationales.     

Sensorimotor system measurement techniques

Objective: To provide an overview of currently available sensorimotor assessment techniques.Data Sources: We drew information from an extensive review of the scientific literature conducted in the areas of proprioception, neuromuscular control, and motor control measurement. Literature searches were conducted using MEDLINE for the years 1965 to 1999 with the key words proprioception, somatosensory evoked potentials, nerve conduction testing, electromyography, muscle dynamometry, isometric, isokinetic, kinetic, kinematic, posture, equilibrium, balance, stiffness, neuromuscular, sensorimotor, and measurement. Additional sources were collected using the reference lists of identified articles.Data Synthesis: Sensorimotor measurement techniques are discussed with reference to the underlying physiologic mechanisms, influential factors and locations of the variable within the system, clinical research questions, limitations of the measurement technique, and directions for future research.Conclusions/Recommendations: The complex interactions and relationships among the individual components of the sensorimotor system make measuring and analyzing specific characteristics and functions difficult. Additionally, the specific assessment techniques used to measure a variable can influence attained results. Optimizing the application of sensorimotor research to clinical settings can, therefore, be best accomplished through the use of common nomenclature to describe underlying physiologic mechanisms and specific measurement techniques.     

Movement-related skin strain associated with goal-oriented lip actions

 It is generally accepted that sensory input contributes to the generation of natural movements. In most motor systems, muscle spindles, tendon organs, joint receptors, and cutaneous mechanoreceptors may provide proprioceptive information. However, the perioral area of the human face lacks muscle spindles, tendon organs, and joint receptors and is therefore a model system for the study of cutaneous afferent contributions to proprioception. This investigation examined a series of skin strains associated with lower-lip movements in human subjects to determine if such strains, which serve as stimuli for cutaneous mechanoreceptors, may underlie proprioception in the face. The results suggested that strains associated with lower-lip movements were of sufficient magnitude to elicit cutaneous mechanoreceptor discharge, as shown in recent human microneurographic studies. Further, the magnitude of multiple strains was predictive of lower-lip movement endpoints. These results highlight the potential importance of cutaneous mechanoreceptors as putative proprioceptors. Received: 16 February 1998 / Accepted: 26 May 1998     

Receptors in the knee joint ligaments and their role in the biomechanics of the joint

The knee joint ligaments contain Ruffini, Pacinian, Golgi, and free-nerve endings with different capabilities of providing the CNS with information about movement and position as well as about noxious events. Skeletomotor neurons (alpha-motoneurons) are known to be influenced only very rarely and weakly from low-threshold mechanoreceptors in the ligaments, while the effects on the tau-muscle-spindle system in the muscles around the knee are so potent that even ligament stretches at very low loads may induce major changes in the responses of the muscle spindle afferents. Since the primary muscle spindle afferents participate in the regulation of muscular stiffness, the receptors in the knee joint ligaments probably contribute, via the tau-muscle-spindle system, to preparatory adjustment (pre-setting) of the stiffness of the muscles around the knee joint, and thereby to the joint stiffness and the functional joint stability.     

Muscle stiffness and spinal stretch reflex sensitivity in the triceps surae

CONTEXT: Greater musculotendinous stiffness may enhance spinal stretch reflex sensitivity by improving mechanical coupling of the muscle spindle and the stretch stimulus. This heightened sensitivity would correspond with a shorter latency and higher-amplitude reflex response, potentially enhancing joint stability. OBJECTIVE: To compare spinal stretch reflex latency and amplitude across groups that differed in musculotendinous stiffness. DESIGN: Static group comparisons. SETTING: Research laboratory. PATIENTS OR OTHER PARTICIPANTS: Forty physically active individuals (20 men, 20 women). Intervention(s): We verified a sex difference in musculotendinous stiffness and compared spinal stretch reflex latency and amplitude in high-stiffness (men) and low-stiffness (women) groups. We also evaluated relationships between musculotendinous stiffness and spinal stretch reflex latency and amplitude, respectively. MAIN OUTCOME MEASURE(S): Triceps surae musculotendinous stiffness and soleus spinal stretch reflex latency and amplitude were assessed at 30% of a maximal voluntary isometric plantar-flexion contraction. RESULTS: The high-stiffness group demonstrated significantly greater stiffness (137.41 +/- 26.99 N/cm) than the low-stiffness group did (91.06 +/- 20.10 N/cm). However, reflex latency (high stiffness = 50.11 +/- 2.07 milliseconds, low stiffness = 48.26 +/- 2.40 milliseconds) and amplitude (high stiffness = 0.28% +/- 0.12% maximum motor response, low stiffness = 0.31% +/- 0.16% maximum motor response) did not differ significantly across stiffness groups. Neither reflex latency (r = .053, P = .746) nor amplitude (r = .073, P = .653) was related significantly to musculotendinous stiffness. CONCLUSIONS: A moderate level of pretension (eg, 30%) likely eliminates series elastic slack; thus, a greater change in force per unit-of-length change (ie, heightened stiffness) would have minimal effects on coupling of the muscle spindle and the stretch stimulus and, therefore, on spinal stretch reflex sensitivity. It appears unlikely that differences in musculotendinous stiffness influenced spinal stretch reflex sensitivity when initiated from a moderate level of pretension. Consequently, differences in musculotendinous stiffness did not appear to influence dynamic joint stability with respect to reflexive neuromuscular control.     

The transduction properties of diaphragmatic mechanoreceptors

The transduction properties of diaphragmatic mechanoreceptors were studied using an isolated organ preparation. Following localization of their receptive field and receptor characterization, controlled diaphragmatic stretch in 2 mm increments was performed while recording the steady-state firing frequency of these afferents. Of 31 receptors recorded, 14 could be categorized into one of 3 types: (1) muscle spindles, (2) Golgi tendon organs, and (3) pressure-sensitive mechanoreceptors. These receptors were also found to be widely distributed in the diaphragm. Four of the muscle spindles examined were shown to possess a length sensitivity of 4-8 mm with a wide range of maximal discharge. The results of this study suggest that the diaphragm contains mechanoreceptors that transduce muscle length and projects this information regarding respiratory proprioception to the CNS.     

Local subcutaneous and muscle pain impairs detection of passive movements at the human thumb

Activity in both muscle spindle endings and cutaneous stretch receptors contributes to the sensation of joint movement. The present experiments assessed whether muscle pain and subcutaneous pain distort proprioception in humans. The ability to detect the direction of passive movements at the interphalangeal joint of the thumb was measured when pain was induced experimentally in four sites: the flexor pollicis longus (FPL), the subcutaneous tissue overlying this muscle, the flexor carpi radialis (FCR) muscle and the subcutaneous tissue distal to the metacarpophalangeal joint of thumb. Tests were conducted when pain was at a similar subjective intensity. There was no significant difference in the ability to detect flexion or extension under any painful or non-painful condition. The detection of movement was significantly impaired when pain was induced in the FPL muscle, but pain in the FCR, a nearby muscle that does not act on the thumb, had no effect. Subcutaneous pain also significantly impaired movement detection when initiated in skin overlying the thumb, but not in skin overlying the FPL muscle in the forearm. These findings suggest that while both muscle and skin pain can disturb the detection of the direction of movement, the impairment is site-specific and involves regions and tissues that have a proprioceptive role at the joint. Also, pain induced in FPL did not significantly increase the perceived size of the thumb. Proprioceptive mechanisms signalling perceived body size are less disturbed by a relevant muscle nociceptive input than those subserving movement detection. The results highlight the complex relationship between nociceptive inputs and their influence on proprioception and motor control.     

Stochastic resonance electrical stimulation to improve proprioception in knee osteoarthritis

Proprioceptive deficits occur with knee osteoarthritis (OA) and improving proprioception may slow joint degeneration by allowing more appropriate joint loading. Stochastic resonance (SR) stimulation improves balance and the sensitivity of specific mechanoreceptors. Our purpose was to evaluate the effects of SR electrical stimulation combined with a knee sleeve on proprioception in subjects with knee OA. Joint position sense (JPS) was measured in 38 subjects with knee OA during four conditions in both a partial weight-bearing (PWB) and non weight-bearing (NWB) task: no electrical stimulation/no sleeve, no electrical stimulation/sleeve, 50 μA-RMS stimulation/sleeve, and 75 μA-RMS stimulation/sleeve. Subjects also reported their knee pain, stiffness, functionality (WOMAC), and instability. Repeated measures ANOVA and Spearman correlations were performed to investigate differences between the conditions and relationships among the outcome measures. JPS during the 75 μA-RMS stimulation/sleeve and sleeve alone conditions was significantly improved compared to the control condition in the PWB task. However, the 75 μA-RMS stimulation/sleeve and the sleeve alone conditions did not differ from each other. A moderate correlation was found between the improvements with the 75 μA-RMS stimulation/sleeve condition compared to the JPS of the control condition in the PWB task. No differences in JPS were found between the four conditions in the NWB task. Significant correlations were found between the control JPS and WOMAC indices (p < 0.005). Improved proprioception during the PWB task was achieved with a sleeve alone and in combination with SR stimulation. The observed correlations suggest that subjects with larger proprioceptive deficits may benefit most from these therapies.     

Sex Differences in 2-DOF Human Ankle Stiffness in Relaxed and Contracted Muscles

Ankle stiffness has been known as one of the most important components contributing to the maintenance of lower body stability during postural balance and locomotion. It has been repeatedly shown that women have lower stability and increased risk of injury when compared to men participating in similar sports activities, yet sex differences in neuromuscular control of the ankle, including the modulation of ankle stiffness, and their contribution to stability remain unknown. To identify sex differences in human ankle stiffness, this study quantified multi-dimensional ankle stiffness in 20 young, healthy men and 20 young, healthy women over a range of ankle muscle contractions, from relaxed to 20% of maximum voluntary co-contraction of ankle muscles. A wearable ankle robot and a system identification method were used to reliably quantify ankle stiffness in a 2-dimensional space spanning the sagittal plane and the frontal plane. In all muscle activation levels, significant sex differences in ankle stiffness were identified in both the sagittal and frontal planes. In the given experimental conditions, ankle stiffness in males was higher than females up to 15.1 and 8.3 Nm/rad in the sagittal plane and the frontal plane, respectively. In addition, sex differences in the spatial structure of ankle stiffness were investigated by quantifying three parameters defining the stiffness ellipse of the ankle: area, aspect ratio, and orientation. In all muscle activation levels, a significant sex difference was identified in the area of stiffness ellipse as expected from the sex difference in the sagittal and frontal planes. However, no statistical sex difference was observed in the aspect ratio and orientation, which would be due to little differences in major anatomical configurations of the ankle joint between sexes. This study, in combination with future studies investigating sex differences during dynamic tasks (e.g. postural balance and locomotion) would serve as a basis to develop a risk assessment tool and sex-specific training programs for efficient ankle injury prevention or rehabilitation.     

Neuromuscular reflexes contribute to knee stiffness during valgus loading

We have previously shown that abduction angular perturbations applied to the knee consistently elicit reflex responses in knee joint musculature. Although a stabilizing role for such reflexes is widely proposed, there are as of yet no studies quantifying the contribution of these reflex responses to joint stiffness. In this study, we estimate the mechanical contributions of muscle contractions elicited by mechanical excitation of periarticular tissue receptors to medial-lateral knee joint stiffness. We hypothesize that these reflex muscle contractions will significantly increase knee joint stiffness in the adduction/abduction direction and enhance the overall stability of the knee. To assess medial-lateral joint stiffness, we applied an abducting positional deflection to the fully extended knee using a servomotor and recorded the torque response using a six degree-of-freedom load-cell. EMG activity was also recorded in both relaxed and preactivated quadriceps and hamstrings muscles with surface electrodes. A simple, linear, second-order, delayed model was used to describe the knee joint dynamics in the medial/lateral direction. Our data indicate that excitation of reflexes from periarticular tissue afferents results in a significant increase of the joint's adduction-abduction stiffness. Similar to muscle stretch reflex action, which is modulated with background activation, these reflexes also show dependence on muscle activation. The potential significance of this reflex stiffness during functional tasks was also discussed. We conclude that reflex activation of knee muscles is sufficient to enhance joint stabilization in the adduction/abduction direction, where knee medial-lateral loading arises frequently during many activities.     

The influence of visual perturbations on the neural control of limb stiffness

To adapt to novel unstable environments, the motor system modulates limb stiffness to produce selective increases in arm stability. The motor system receives information about the environment via somatosensory and proprioceptive signals related to the perturbing forces and visual signals indicating deviations from an expected hand trajectory. Here we investigated whether subjects modulate limb stiffness during adaptation to a purely visual perturbation. In a first experiment, measurements of limb stiffness were taken during adaptation to an elastic force field (EF). Observed changes in stiffness were consistent with previous reports: subjects increased limb stiffness and did so only in the direction of the environmental instability. In a second experiment, stiffness changes were measured during adaptation to a visual perturbing environment that magnified hand-path deviations in the lateral direction. In contrast to the first experiment, subjects trained in this visual task showed no accompanying change in stiffness, despite reliable improvements in movement accuracy. These findings suggest that this sort of visual information alone may not be sufficient to engage neural systems for stiffness control, which may depend on sensory signals more directly related to perturbing forces, such as those arising from proprioception and somatosensation.     

Directional invariance during loading-related modulations of muscle activity: evidence for motor equivalence

In the present study, we investigated the influence of external force manipulations on movements in different directions, while keeping the amplitude invariant. Subjects (n=10) performed a series of cyclical anteroposterior, mediolateral, and oblique line-drawing movements (star drawing task) with their dominant limb in the horizontal plane. To dissociate kinematics from the underlying patterns of muscle activation, spring loading was applied to the forearm of the moving limb. Whereas spring loading of the arm resulted in considerable changes in the overall amount of muscle activation in the elbow and shoulder muscles, invariance was largely maintained at the kinematic level. Subjects produced the required movement directions and amplitudes of the star drawing largely successfully, irrespective of the force bias induced by the spring. These observations demonstrate motor equivalence and strengthen the notion that the spatial representation of drawing movements is encoded in the higher brain regions in a rather abstract form that is dissociated from the concrete muscle activation patterns underlying a particular movement direction. To achieve this goal, the central nervous system shifted between two or more muscle grouping strategies to overcome modulations in the interaction among posture-dependent (joint stiffness), dynamic (inertial), and elastic (spring) torque components in the joints. Spring loading induced general changes in the overall amount of EMG activity, which was largely muscle but not direction specific, presumably to represent the posture-dependent biasing force of the spring. Loading was mainly shown to increase muscle coactivation in the elbow joint. This indicates that the subjects tended to increase stiffness in the elbow to compensate for changes in the spring bias forces in order to minimize trajectory errors. Changes in muscle grouping of the shoulder antagonists were mainly a consequence of movement direction but were also affected partly by loading, presumably reflecting the influence of dynamic force components. Taken together, the results confirmed the hypothesis that changes of movement direction and direction of force in the end-effector generated specific sets of muscle grouping to overcome the dynamic requirements in the joints while keeping the kinematics largely unchanged. This suggests that directional tuning in muscle activity and changes in muscle grouping reflects the formation of appropriate internal models in the CNS that give rise to motor equivalence. Electronic Publication     

The role of limb torque, muscle action and proprioception during closed kinetic chain rehabilitation of the lower extremity

This paper defines the differences between open and closed kinetic chain exercise and explains the role of limb torque, muscle action, and proprioception during rehabilitation of the lower extremity. Closed kinetic chain rehabilitation is shown to decrease shear forces, increase proprioception, and increase muscle group coordination through examples of progressive exercises. The authors conclude that closed kinetic chain rehabilitation is an economical, efficient, and effective means of rehabilitation, with the ultimate goal of enhancing proprioception, thus gaining lower extremity joint stability.     

Multijoint muscle regulation mechanisms examined by measured human arm stiffness and EMG signals

Stiffness properties of the musculo-skeletal system can be controlled by regulating muscle activation and neural feedback gain. To understand the regulation of multijoint stiffness, we examined the relationship between human arm joint stiffness and muscle activation during static force control in the horizontal plane by means of surface electromyographic (EMG) studies. Subjects were asked to produce a specified force in a specified direction without cocontraction or they were asked to keep different cocontractions while producing or not producing an external force. The stiffness components of shoulder, elbow, and their cross-term and the EMG of six related muscles were measured during the tasks. Assuming that the EMG reflects the corresponding muscle stiffness, the joint stiffness was predicted from the EMG by using a two-link six-muscle arm model and a constrained least-square-error regression method. Using the parameters estimated in this regression, single-joint stiffness (diagonal terms of the joint-stiffness matrix) was decomposed successfully into biarticular and monoarticular muscle components. Although biarticular muscles act on both shoulder and elbow, they were found to covary strongly with elbow monoarticular muscles. The preferred force directions of biarticular muscles were biased to the directions of elbow monoarticular muscles. Namely, the elbow joint is regulated by the simultaneous activation of monoarticular and biarticular muscles, whereas the shoulder joint is regulated dominantly by monoarticular muscles. These results suggest that biarticular muscles are innervated mainly to control the elbow joint during static force-regulation tasks. In addition, muscle regulation mechanisms for static force control tasks were found to be quite different from those during movements previously reported. The elbow single-joint stiffness was always higher than cross-joint stiffness (off-diagonal terms of the matrix) in static tasks while elbow single-joint stiffness is reported to be sometimes as small as cross-joint stiffness during movement. That is, during movements, the elbow monoarticular muscles were occasionally not activated when biarticular muscles were activated. In static tasks, however, monoarticular muscle components in single-joint stiffness were increased considerably whenever biarticular muscle components in single- and cross-joint stiffness increased. These observations suggest that biarticular muscles are not simply coupled with the innervation of elbow monoarticular muscles but also are regulated independently according to the required task. During static force-regulation tasks, covariation between biarticular and elbow monoarticular muscles may be required to increase stability and/or controllability or to distribute effort among the appropriate muscles.     

踝关节本体感觉的测量方法研究与应用

背景：踝关节本体感觉能力的降低可能是踝关节容易反复损伤的一个重要原因,而对于踝关节本体感觉的定量评定方法一直没有一个标准化的测试方法。 目的：通过查阅大量资料并进行分析总结,对踝关节本体感觉的测量方法的研究现状进行综述。 方法：由作者检索PubMed数据库及维普数据库的相关文章。英文检索词为“joint position sense,muscle force sense;balance capacity;proprioception;ankle joint”;中文检索词为“本体感觉,平衡能力,踝关节”。共入选53篇文献进行归纳总结。 结果与结论：踝关节本体感觉的测量方法包括关节位置觉、肌肉力觉、侦测被动运动变化阈值、关节运动觉、平衡能力等,在实际应用中应根据实际情况需要来确定选用哪种方法作为踝关节本体感觉的测量方法。     

A model of dynamic sacro-iliac joint instability from malrecruitment of gluteus maximus and biceps femoris muscles resulting in low back pain

The objective of this work is to propose a biomechanical model of sacro-iliac joint dysfunction as a cause of low back pain. Sacro-iliac joint is known to be a source of low back pain. We also know that it is a very stable joint with little mobility. Surrounding lower limb and back muscles contribute a major part of this stability. Gait analysis studies have revealed an orderly sequence of muscle activation when we walk - that contributes to efficient stabilisation of the joint and effective weight transfer to the lower limb. Gluteus maximus fibres-lying almost perpendicular to the joint surfaces are ideally oriented for this purpose. Biceps femoris is another important muscle that can also influence joint stability by its proximal attachment to sacrotuberous ligament. Altered pattern of muscle recruitment has been observed in patients with low back pain. But we do not know the exact cause-effect relationship. Because of its position as a key linkage in transmission of weight from the upper limbs to the lower, poor joint stability could have major consequences on weight bearing. It is proposed that sacro-iliac joint dysfunction can result from malrecruitment of gluteus maximus motor units during weight bearing. This results in compensatory biceps over activation. The resulting soft tissue strain and joint instability may manifest itself in low back pain. If our hypothesis holds true, it may have positive implications for patients with sacro-iliac joint dysfunction - who could be offered a definite diagnosis and targeted physiotherapy. It may be possible to identify patients early in a primary care setting and offer direct physio referral. They could benefit from exercises to improve strengthening and recruitment of the affected muscles.     

The Sensory Innervation of the Human Pharynx: Searching for Mechanoreceptors

The coordinate neural regulation of the upper airways muscles is basic to control airway size and resistance. The superior constrictor pharyngeal muscle (SCPM) forms the main part of the lateral and posterior walls of the pharynx and typically is devoid of muscle spindles, the main type of proprioceptor. Because proprioception arising from SCPM is potentially important in the physiology of the upper airways, we have investigated if there are mechanical sensory nerve endings substitute for the muscle spindles. Samples of human pharynx were analyzed using immunohistochemistry associated to general axonic and Schwann cells markers (NSE, PGP 9.5, RT‐97, and S100P), intrafusal muscle fiber markers, and putative mechanical sense proteins (TRPV4 and ASIC2). Different kinds of sensory corpuscles were observed in the pharynx walls (Pacini‐like corpuscles, Ruffini‐like corpuscles, spiral‐wharves nerve structures, and others) which are supplied by sensory nerves and express putative mechanoproteins. No evidence of muscle spindles was observed. The present results demonstrate the occurrence of numerous and different morphotypes of sensory corpuscles/mechanoreceptors in human pharynx that presumably detect mechanical changes in the upper airways and replace muscle spindles for proprioception. Present findings are of potential interest for the knowledge of pathologies of the upper airways with supposed sensory pathogenesis. Anat Rec, 296:1735–1746, 2013. © 2013 Wiley Periodicals, Inc.     

Reflex control of dynamic muscle stiffness in a slow crustacean muscle

The properties of a stretch reflex in the ventral superficial muscle of the hermit crab abdomen were studied in an isolated abdominal preparation to determine how the reflex affects the mechanical properties of the muscle and whether the reflex is controlling length, force, or stiffness. The reflex was elicited by stretch of hypodermal mechanoreceptors in the cuticle and resulted in the activation of excitor motoneurons to both circular and longitudinal layers of the muscle, thus stiffening the abdomen. The medial motoneuron of the longitudinal layer of the right fourth segment was selected for detailed analysis. It was tonically active and responded to stretch with a phasic burst having a latency of 100 ms. Reflex muscle tension began to increase at 130 ms and reached a peak at 300 ms. Reflex-burst frequency increased slightly with stretch amplitude. Peak force was an approximately linear function of stretch amplitude. No tonic component to the reflex was found in the medial motoneuron, in the central motoneuron (the smallest excitor to the muscle), or in the medial motoneuron studied in intact animals. The reflex-burst frequency was a function of stretch velocity, increasing between two and one-half to four times for a 10-fold increase in stretch velocity. Peak force was essentially independent of stretch velocity over this range. The reflex-burst frequency was not a function of the initial length of the muscle on the ascending limb of the length-tension relation. Active peak force (between two and three times passive peak force) was relatively constant over this range. The dynamic active stiffness (the resistance to stretch of the muscle when the nervous system was intact) was separated into two components. One component is that due to the tonic frequency of the motoneurons, the other to the reflex burst. The reflex component makes up a substantial part of the total active stiffness. Dynamic active stiffness is relatively constant under the conditions of these experiments and, when normalized, is similar to that observed in mammalian myotatic reflexes. This constancy, however, cannot be due to negative feedback control of stiffness, as in mammals. It is suggested that constant reflex stiffness arises from the combination of the low-pass filter characteristics of the muscle and the high-pass filter characteristics of the reflex over a restricted range of velocities.(ABSTRACT TRUNCATED AT 400 WORDS)     

Strength Training and Shoulder Proprioception

Context:

Proprioception is essential to motor control and joint stability during daily and sport activities. Recent studies demonstrated that athletes have better joint position sense (JPS) when compared with controls matched for age, suggesting that physical training could have an effect on proprioception.

Objective:

To evaluate the result of an 8-week strength-training program on shoulder JPS and to verify whether using training intensities that are the same or divergent for the shoulder''s dynamic-stabilizer muscles promote different effects on JPS.

Design:

Randomized controlled clinical trial.

Setting:

We evaluated JPS in a research laboratory and conducted training in a gymnasium.

Patients or Other Participants:

A total of 90 men, right handed and asymptomatic, with no history of any type of injury or shoulder instability.

Intervention(s):

For 8 weeks, the participants performed the strength-training program 3 sessions per week. We used 4 exercises (bench press, lat pull down, shoulder press, and seated row), with 2 sets each.

Main Outcome Measure(s):

We measured shoulder JPS acuity by calculating the absolute error.

Results:

We found an interaction between group and time. To examine the interaction, we conducted two 1-way analyses of variance comparing groups at each time. The groups did not differ at pretraining; however, a difference among groups was noted posttraining.

Conclusions:

Strength training using exercises at the same intensity produced an improvement in JPS compared with exercises of varying intensity, suggesting that the former resulted in improvements in the sensitivity of muscle spindles and, hence, better neuromuscular control in the shoulder.Key Words: joint position sense, neuromuscular control, muscle spindles

Key Points

• Improvements in joint position sense can be attained via standard strength-training exercises.
• Performing resistance exercises at consistent intensity rather than varying intensity resulted in better proprioception performance.

Improving muscle strength for joint stability is a goal of physical training for the shoulder.^1–3 According to Myers and Lephart,⁴ the rotator cuff, deltoid, biceps, teres major, latissimus dorsi, and pectoralis major muscles are responsible for providing shoulder stabilization. Inman et al⁵ were the first to state that the coactivation force of the shoulder''s dynamic stabilizers provides the joint stability. However, joint mechanics and stability may be compromised if such forces are not equalized. Therefore, in order to achieve joint stability, training must be directed at attaining proportional strength around the joint. Two main aspects should be taken into account during strength training: a specific muscle-force level and the force balance among muscles that act on the same joint.^3,6Shoulder-joint stability is the result of passive and dynamic components.⁷ The bone geometry, relative intra-articular pressure, glenohumeral labrum, and capsuloligamentous structures are passive components,⁴ whereas dynamic components are provided by contractile muscle activity coordinated around the joint and modulated by the neuromuscular system.⁸ The basis of passive and dynamic interactions is the proprioceptive information emerging from mechanoreceptors in muscles, tendons, joint-capsule ligaments, and skin, which are centrally integrated.^7,9 In this context, kinesthesia, joint position, and force sense are described as proprioception submodalities.^4,10–12Proprioception is essential to motor control and joint stability during daily activities and sports practice.^10,11 Thus, proprioception can be defined as the ability to recognize and to locate the body in relation to its position and orientation in space.^13,14 Allegrucci et al¹⁵ identified kinesthetic deficits in the dominant shoulder of throwing athletes as a mechanism for shoulder instability. The same result was found by Safran et al.¹⁶ Conversely, a recent study¹⁷ demonstrated that athletes have better joint position sense (JPS) than controls matched for age, suggesting that sport activity could have an effect on proprioception. Despite this result, the effect of strength training on proprioception remains unclear, although some authors^17–20 have described the effects of muscle strengthening on proprioception. These researchers hypothesized that strength training directly affects the functional capacity of the dynamic stabilizers. For this reason, it is important to understand the effects of this training on proprioception so that we can improve the strength-training protocols to increase joint stability.However, the effects of different strength-training programs on the JPS of healthy individuals remain debatable. Therefore, the focus of our study was to (1) evaluate the effect of 8 weeks of strength training on shoulder JPS and (2) verify whether using the same or divergent training intensities for the shoulder muscles'' stability produced any significant effects on JPS. We hypothesized that the JPS would be improved by strength training and that different strategies to control training intensity would promote different responses with regard to shoulder proprioception.     

The effect of high-frequency cutaneous vibration on different inputs subserving detection of joint movement

Stimuli that preferentially activate rapidly adapting cutaneous receptors impair proprioception in the fingers. These experiments assessed potential mechanisms. The ability to detect passive movements about interphalangeal joints of the fingers was measured when vibrotactile stimuli were applied to the moving digit or to an adjacent digit at a high frequency (300 Hz) and low amplitude (50 μm peak-to-peak) that favours activation of Pacinian corpuscle (PC) afferents. Detection of movement was significantly impaired when vibration was applied to either digit. However, vibration applied to an anaesthetized adjacent digit caused no impairment. Impairment of proprioception was still observed when only skin and joint (but not muscle) afferents could contribute to detection, but was not significant with only muscle afferents intact during anaesthesia of the moving digit. We suggest that activation of PC afferents, either in or near the moving digit, impairs movement detection through an interaction predominantly between the classes of cutaneous afferents.