Upper trapezius muscle activity in healthy office workers: reliability and sensitivity of occupational exposure measures to differences in sex and hand dominance.

Patterns of cervical muscle activity may contribute to overuse injuries in office workers. The purpose of this investigation was to characterise patterns of upper trapezius muscle activity in pain-free office workers using traditional occupational exposure measures and a modified Active Amplitude Probability Distribution Function (APDF), which considers only periods of active muscle contraction. Bilateral trapezius muscle activity was recorded in 77 pain-free office workers for 1-2 full days in their natural work environment. Mean amplitude, gap frequency, muscular rest and Traditional and Active APDF amplitudes were calculated. All measures demonstrated fair to substantial reliability. Dominant muscles demonstrated higher amplitudes of activity and less muscular rest compared to non-dominant, and women demonstrated less muscular rest with no significant difference in amplitude assessed by Active APDF compared to men. These findings provide normative data to identify atypical motor patterns that may contribute to persistence or recurrence of neck pain in office workers. Practitioner Summary: Upper trapezius muscle activity was characterised in a large cohort of pain-free workers using electromyographic recordings from office environments. Dominant muscles demonstrated higher activity and less rest than non-dominant, and women demonstrated less rest than men. Results may be used to identify atypical trapezius muscle activity in office workers.

Mechanical pain sensitivity and the severity of chronic neck pain and disability are not modulated across the menstrual cycle.

UNLABELLED: Despite the high prevalence of neck pain among women, menstrual effects on regional pain outcomes have not been investigated in this clinical population. This study evaluated menstrual effects on mechanical pain sensitivity (pressure pain threshold [PPT]), neck pain intensity (numeric pain rating scale [NPRS]), and neck-related disability (Neck Disability Index [NDI]) in 22 normally menstruating (NM) and 17 hormonal contraceptive users with chronic neck pain. Sex hormones, PPT, and NDI were measured during the early follicular (F1), late follicular (F2), and luteal (L) menstrual phases. Daily NPRS scores were recorded in an online symptom diary and averaged within each phase. Estradiol and progesterone increased only for NM women in F2 and L, respectively. Phase effects on PPT (η(2) = .003), NDI (η(2) = .003), and NPRS (η(2) = .016) for NM women were small and did not differ from those for the hormonal contraceptive users (P ≥ .386). Averaged across the menstrual cycle, PPT scores explained 29% of the variance in NPRS scores for NM women but were not associated with NDI scores in either group. Results indicate that the magnitude of menstrual effects on mechanical pain sensitivity and the severity of neck pain and disability do not exceed thresholds of clinically detectable change in women with chronic neck pain. PERSPECTIVE: Fluctuations in evoked and clinical pain outcomes across the menstrual cycle do not appear to be of sufficient magnitude to impact clinical decision making for women with chronic neck pain.

Does delay in total knee arthroplasty impact postoperative performance? A case-based illustration.

Optimal timing of TKA surgery is not clear. This report describes a patient's tested strength and function deficits before and after a surgical delay compared with a comparable cohort. TKA for OA was postponed due to non-health issues. Strength and functional performance were tested at 3 points preoperatively and 4 points postoperatively. Preoperative strength and functional performance precipitously declined during surgical delay. Quadriceps strength declined 47% from 6 months to one week pre-operatively, with the majority of this decline in the last 3 months. Pain levels peaked preoperatively, averaging 8.3/10. After 6 weeks of TKA, quadriceps recovered to immediate preoperative strength, but was 47% less than 6 months preoperatively. Function improved to 6 months preoperative levels by 6 weeks. Functional performance recovered to immediate preoperative levels by 6 months, while muscle strength (quadriceps and hamstrings) did not. This case describes a precipitous decline in strength and function during a 6-month surgical delay, with poorer recovery compared with a cohort without delay. While this case only describes a single individual, the results highlight the need for further research on optimal surgical timing for total knee arthroplasty, considering function, strength and pain levels, especially because strength recovery can have long-term implications.

Stress management as an adjunct to physical therapy for chronic neck pain.

BACKGROUND AND PURPOSE: Chronic neck pain is prevalent in the workplace. Research suggests that psychosocial stress may contribute to the development of neck pain by causing excessive or prolonged muscle activity in some individuals. The purpose of this case report is to describe the rationale, development, and implementation of stress management as an adjunct to standard physical therapist management of chronic neck pain in a female office worker who responded to psychosocial stress with elevated muscle activity prior to treatment. CASE DESCRIPTION: A 44-year-old female office employee with an 8-year history of chronic neck pain participated in this case report. The patient was selected from a group of research participants who demonstrated elevated electromyographic (EMG) activity of the trapezius muscle in response to simulated occupational stressors. The multidisciplinary intervention consisted of 8 physical therapy sessions, supplemented by 8 stress management sessions that included EMG biofeedback and psychotherapy to facilitate muscle relaxation. OUTCOMES: Neck disability decreased by 50%, trait anxiety decreased by 21%, and the duration of trapezius muscle rest in the workplace increased by 56% immediately after the 8-week intervention. These improvements were maintained 6 months after treatment, and the patient reported a complete absence of neck disability at the 2-year follow-up assessment. DISCUSSION: A sustained reduction in neck disability was observed for a patient with chronic neck pain after participating in a multidisciplinary intervention that combined physical therapy and stress management approaches to facilitate muscle relaxation in the workplace. Future clinical trials are needed to assess whether stress management is a useful adjunct therapy for patients with chronic neck pain who show elevated muscle activity in response to psychosocial stress.

Relationship between intensity of quadriceps muscle neuromuscular electrical stimulation and strength recovery after total knee arthroplasty.

BACKGROUND: Neuromuscular electrical stimulation (NMES) can facilitate the recovery of quadriceps muscle strength after total knee arthroplasty (TKA), yet the optimal intensity (dosage) of NMES and its effect on strength after TKA have yet to be determined. OBJECTIVE: The primary objective of this study was to determine whether the intensity of NMES application was related to the recovery of quadriceps muscle strength early after TKA. A secondary objective was to quantify quadriceps muscle fatigue and activation immediately after NMES to guide decisions about the timing of NMES during rehabilitation sessions. DESIGN: This study was an observational experimental investigation. METHODS: Data were collected from 30 people who were 50 to 85 years of age and who received NMES after TKA. These people participated in a randomized controlled trial in which they received either standard rehabilitation or standard rehabilitation plus NMES to the quadriceps muscle to mitigate strength loss. For the NMES intervention group, NMES was applied 2 times per day at the maximal tolerable intensity for 15 contractions beginning 48 hours after surgery over the first 6 weeks after TKA. Neuromuscular electrical stimulation training intensity and quadriceps muscle strength and activation were assessed before surgery and 3.5 and 6.5 weeks after TKA. RESULTS: At 3.5 weeks, there was a significant association between NMES training intensity and a change in quadriceps muscle strength (R(2)=.68) and activation (R(2)=.22). At 6.5 weeks, NMES training intensity was related to a change in strength (R(2)=.25) but not to a change in activation (R(2)=.00). Furthermore, quadriceps muscle fatigue occurred during NMES sessions at 3.5 and 6.5 weeks, whereas quadriceps muscle activation did not change. LIMITATIONS: Some participants reached the maximal stimulator output during at least 1 treatment session and might have tolerated more stimulation. CONCLUSIONS: Higher NMES training intensities were associated with greater quadriceps muscle strength and activation after TKA.

Early neuromuscular electrical stimulation to improve quadriceps muscle strength after total knee arthroplasty: a randomized controlled trial.

BACKGROUND: The recovery of quadriceps muscle force and function after total knee arthroplasty (TKA) is suboptimal, which predisposes patients to disability with increasing age. OBJECTIVE: The purpose of this investigation was to evaluate the efficacy of quadriceps muscle neuromuscular electrical stimulation (NMES), initiated 48 hours after TKA, as an adjunct to standard rehabilitation. DESIGN: This was a prospective, longitudinal randomized controlled trial. METHODS: Sixty-six patients, aged 50 to 85 years and planning a primary unilateral TKA, were randomly assigned to receive either standard rehabilitation (control) or standard rehabilitation plus NMES applied to the quadriceps muscle (initiated 48 hours after surgery). The NMES was applied twice per day at the maximum tolerable intensity for 15 contractions. Data for muscle strength, functional performance, and self-report measures were obtained before surgery and 3.5, 6.5, 13, 26, and 52 weeks after TKA. RESULTS: At 3.5 weeks after TKA, significant improvements with NMES were found for quadriceps and hamstring muscle strength, functional performance, and knee extension active range of motion. At 52 weeks, the differences between groups were attenuated, but improvements with NMES were still significant for quadriceps and hamstring muscle strength, functional performance, and some self-report measures. LIMITATIONS: Treatment volume was not matched for both study arms; NMES was added to the standard of care treatment. Furthermore, testers were not blinded during testing, but used standardized scripts to avoid bias. Finally, some patients reached the maximum stimulator output during at least one treatment session and may have tolerated more stimulation. CONCLUSIONS: The early addition of NMES effectively attenuated loss of quadriceps muscle strength and improved functional performance following TKA. The effects were most pronounced and clinically meaningful within the first month after surgery, but persisted through 1 year after surgery.

Functional performance and muscle strength phenotypes in men and women with Danon disease.

Danon disease is a rare X-linked myopathy that is characterized clinically by a triad of cardiomyopathy, skeletal myopathy, and cognitive impairment. The purpose of this investigation was to quantify functional performance, muscle weakness, and quadriceps activation in individuals with Danon disease as compared with healthy individuals. Four males (ages 10-34 years) and 4 females (ages 16-50 years), with the genetic markers of Danon disease, were compared with 8 healthy males (ages 22-34 years) and 8 healthy females (ages 23-41 years) and previously reported norms. Affected males and females had decreased functional performance, significant generalized muscle weakness, and decreased quadriceps strength and activation when compared with healthy individuals. Affected males had larger deficits in function, strength, and activation when compared with affected females. The results indicate that, although the presentation of Danon disease is variable and is typically only described in males, muscle weakness patterns exist in both affected males and females.

Quadriceps and hamstrings muscle dysfunction after total knee arthroplasty.

BACKGROUND/RATIONALE: Although TKA reliably reduces pain from knee osteoarthritis, full recovery of muscle strength and physical function to normal levels is rare. We presumed that a better understanding of acute changes in hamstrings and quadriceps muscle performance would allow us to enhance early rehabilitation after TKA and improve long-term function. QUESTIONS/PURPOSES: The purposes of this study were to (1) evaluate postoperative quadriceps and hamstrings muscle strength loss after TKA and subsequent recovery using the nonoperative legs and healthy control legs for comparison, and (2) measure hamstrings coactivation before and after TKA during a maximal isometric quadriceps muscle contraction and compare with nonoperative and healthy control legs. METHODS: We prospectively followed 30 patients undergoing TKA at 2 weeks preoperatively and 1, 3, and 6 months postoperatively and compared patient outcomes with a cross-sectional cohort of 15 healthy older adults. Bilateral, isometric strength of the quadriceps and hamstrings was assessed along with EMG measures of hamstrings coactivation during a maximal isometric quadriceps contraction. RESULTS: There were no differences in strength loss or recovery between the quadriceps and hamstrings muscles of the operative leg throughout the followup, although differences existed when compared with nonoperative and healthy control legs. Hamstrings muscle coactivation in the operative leg during a maximal quadriceps effort was elevated at 1 month (144.5%) compared to the nonoperative leg. CONCLUSIONS: Although quadriceps dysfunction after TKA typically is recognized and addressed in postoperative therapy protocols, hamstrings dysfunction also is present and should be addressed. CLINICAL RELEVANCE: Quadriceps and hamstrings muscle strengthening should be the focus of future rehabilitation programs to optimize muscle function and long-term outcomes.

Context-dependent modulation of cutaneous reflex amplitudes during forward and backward leg cycling.

We used amplitude modulation of cutaneous reflexes during leg cycling as a paradigm to investigate neural control mechanisms regulating forward (FWD) and backward (BWD) rhythmic limb movement. Our prediction was a simple reversal of reflex modulation during BWD leg cycling and context-dependent reflex modulation. Cutaneous reflexes were evoked by electrical stimulation delivered to the superficial peroneal (SP) and distal tibial (TIB) nerves at the ankle. EMG recordings were collected from muscles acting at the hip, knee, and ankle. Kinematic data were also collected at these joints. Cutaneous reflexes were analyzed according to the phase of movement in which they were evoked. When functional phases (i.e., flexion or extension) of cycling were matched between FWD and BWD, background EMG and reflex modulation patterns were generally similar. The reflex patterns when compared at similar functional phases presented as a simple reversal suggesting FWD and BWD cycling are regulated by similar neural mechanisms. The general reflex regulation of limb trajectory was maintained between cycling directions in accordance with the task requirements of the movement direction.

Neural regulation of rhythmic arm and leg movement is conserved across human locomotor tasks.

It has been proposed that different forms of rhythmic human limb movement have a common central neural control ('common core hypothesis'), just as in other animals. We compared the modulation patterns of background EMG and cutaneous reflexes during walking, arm and leg cycling, and arm-assisted recumbent stepping. We hypothesized that patterns of EMG and reflex modulation during cycling and stepping (deduced from mathematical principal components analysis) would be comparable to those during walking because they rely on similar neural substrates. Differences between the tasks were assessed by evoking cutaneous reflexes via stimulation of nerves in the foot and hand in separate trials. The EMG was recorded from flexor and extensor muscles of the arms and legs. Angular positions of the hip, knee and elbow joints were also recorded. Factor analysis revealed that across the three tasks, four principal components explained more than 93% of the variance in the background EMG and middle-latency reflex amplitude. Phase modulation of reflex amplitude was observed in most muscles across all tasks, suggesting activity in similar control networks. Significant correlations between EMG level and reflex amplitude were frequently observed only during static voluntary muscle activation and not during rhythmic movement. Results from a control experiment showed that strong correlation between EMG and reflex amplitudes was observed during discrete, voluntary leg extension but not during walking. There were task-dependent differences in reflex modulation between the three tasks which probably arise owing to specific constraints during each task. Overall, the results show strong correlation across tasks and support common neural patterning as the regulator of arm and leg movement during various rhythmic human movements.

Neural coupling between the arms and legs during rhythmic locomotor-like cycling movement.

Neuronal coupling between the arms and legs allowing coordinated rhythmic movement during locomotion is poorly understood. We used the modulation of cutaneous reflexes to probe this neuronal coupling between the arms and legs using a cycling paradigm. Participants performed rhythmic cycling with arms, legs, or arms and legs together. We hypothesized that any contributions from the arms would be functionally linked to locomotion and would thus be phase-dependent. Reflexes were evoked by electrical stimulation of the superficial peroneal nerve at the ankle, and electromyography (EMG) was recorded from muscles in the arms and legs. The main finding was that the relative contribution from the arms and legs was linked to the functional state of the legs. For example, in tibialis anterior, the largest contribution from arm movement [57% variance accounted for (VAF), P < 0.05] was during the leg power phase, whereas the largest from leg movement (71% VAF, P < 0.05) was during leg cycling recovery. Thus the contribution from the arms was functionally gated throughout the locomotor cycle in a manner that appears to support the action of the legs. Additionally, the effect of arm cycling on reflexes in leg muscles when the legs were not moving was relatively minor; full expression of the effect of rhythmic arm movement was only observed when both the arms and legs were moving. Our findings provide experimental support for the interaction of rhythmic arm and leg movement during human locomotion.