Sleep deprivation increases pain sensitivity following acute muscle soreness.

OBJECTIVE: The aim of this cross-sectional group comparison study was to investigate whether sleep disturbance facilitates pain sensitivity caused by an acute muscle injury. METHODS: Thirty-six healthy individuals were included and randomly assigned to one of three groups in a non-balanced manner: a control group (n = 11) and two groups who performed eccentric exercise for quadriceps to cause delayed onset of muscle soreness (DOMS). The difference between the DOMS groups was that one followed their habitual sleep pattern (Sleep group, n = 12) and the other had their sleep withdrawn for one night (No-Sleep group, n = 13). The level of DOMS was indicated using a 6-point Likert Scale and pain sensitivity was assessed using Pressure Pain Thresholds (PPT) at the lower legs and shoulder at baseline (Day-1) and after 48 h (Day-3). Additionally, pain distribution following suprathreshold pressure stimulation (STPS) on the quadriceps muscle was assessed on the same days. RESULTS: PPTs were significantly reduced at Day-3 compared with Day-1 in both DOMS groups. The relative change between days was larger in the No-Sleep group compared with controls (P<0.05) whilst no significant change was seen in the Sleep group compared with controls. Furthermore, no significant differences were found between groups nor days for the subjective perception of DOMS (Likert Scale) and the size of the area of STPS. CONCLUSIONS: The loss of sleep further increases pain sensitivity following an acute soft tissue injury, demonstrating a potential causative role of the lack of sleep on complex pain states following musculoskeletal injuries.

Assessment of range and quality of neck movement using a smartphone-based application.

This study had the objective of measuring the validity of using a smartphone-based application to measure range of motion (ROM) and quality of movement (QOM) of neck motion by comparing it with 3D-motion capture analysis. METHODS: Thirty healthy volunteers participated in this cross-sectional study. A helmet fitted with markers for motion capture analysis and a smartphone were fastened to the head of the participants. The smartphone recorded data using a beta version of Balancy (MEDEI, Denmark). Assessments of full active movement in transverse and sagittal planes were performed. Recordings were made simultaneously with the camera system and the smartphone. ROM and jerkiness were compared with a repeated measures ANOVA and a Pearson product moment was calculated to compare the outcomes from the different applications. Bland-Altman plots were generated to determine the levels of agreement. RESULTS: No difference was found between modalities when comparing measurements of jerkiness or ROM. An excellent Pearson product moment was found for the outcomes of the two modalities for ROM (Pearson's r: 0.83 - 0.96) and jerkiness (Pearson's r: 0.86 - 0.95). The Bland-Altman plot revealed a systemic offset where the phone consistently measured higher values for ROM and lower values for jerkiness. CONCLUSIONS: This study demonstrated that a smartphone-based application can be used to accurately measure ROM and jerkiness during neck movements. These results indicate the utility of using a smartphone-based application to assess neck movement in humans. The findings have implications for assessment of neck movement in research and clinical practice.

Experimental pain in the groin may refer into the lower abdomen: Implications to clinical assessments.

OBJECTIVES: To investigate the effects of experimental adductor pain on the pain referral pattern, mechanical sensitivity and muscle activity during common clinical tests. DESIGN: Repeated-measures design. METHODS: In two separate sessions, 15 healthy males received a hypertonic (painful) and isotonic (control) saline injection to either the adductor longus (AL) tendon to produce experimental groin pain or into the rectus femoris (RF) tendon as a painful control. Pain intensity was recorded on a visual analogue scale (VAS) with pain distribution indicated on body maps. Pressure pain thresholds (PPT) were assessed bilaterally in the groin area. Electromyography (EMG) of relevant muscles was recorded during six provocation tests. PPT and EMG assessment were measured before, during and after experimental pain. RESULTS: Hypertonic saline induced higher VAS scores than isotonic saline (p<0.001), and a local pain distribution in 80% of participants. A proximal pain referral to the lower abdominal region in 33% (AL) and 7% (RF) of participants. Experimental pain (AL and RF) did not significantly alter PPT values or the EMG amplitude in groin or trunk muscles during provocation tests when forces were matched with baseline. CONCLUSIONS: This study demonstrates that AL tendon pain was distributed locally in the majority of participants but may refer to the lower abdomen. Experimental adductor pain did not significantly alter the mechanical sensitivity or muscle activity patterns.

Pressure-induced referred pain is expanded by persistent soreness.

Several chronic pain conditions are accompanied with enlarged referred pain areas. This study investigated a novel method for assessing referred pain. In 20 healthy subjects, pressure pain thresholds (PPTs) were recorded and pressure stimuli (120% PPT) were applied bilaterally for 5 and 60 seconds at the infraspinatus muscle to induce local and referred pain. Moreover, PPTs were measured bilaterally at the shoulder, neck, and leg before, during, and after hypertonic saline-induced referred pain in the dominant infraspinatus muscle. The pressure and saline-induced pain areas were assessed on drawings. Subsequently, delayed onset muscle soreness was induced using eccentric exercise of the dominant infraspinatus muscle. The day-1 assessments were repeated the following day (day 2). Suprathreshold pressure stimulations and saline injections into the infraspinatus muscle caused referred pain to the frontal aspect of the shoulder/arm in all subjects. The 60-second pressure stimulation caused larger referred pain areas compared with the 5-second stimulation (P < 0.01). Compared with pressure stimulation, the saline-induced referred pain area was larger (P < 0.02). After saline-induced pain, the PPTs at the infraspinatus and supraspinatus muscles were reduced (P < 0.05), and the 5-second pressure-induced referred pain area was larger than baseline. Pressure pain thresholds at the infraspinatus and supraspinatus muscles were reduced at day 2 in the delayed onset muscle soreness side (P < 0.05). Compared with day 1, larger pressure and saline-induced referred pain areas were observed on day 2 (P < 0.05). Referred pain to the shoulder/arm was consistently induced and enlarged after 1 day of muscle soreness, indicating that the referred pain area may be a sensitive biomarker for sensitization of the pain system.

Resisted adduction in hip neutral is a superior provocation test to assess adductor longus pain: An experimental pain study.

The criterion of long-standing groin pain diagnoses in athletes usually relies on palpation and clinical tests. An experimental pain model was developed to examine the clinical tests under standardized conditions. Pain was induced by hypertonic saline injected into the proximal adductor longus (AL) tendon or rectus femoris (RF) tendon in 15 healthy male participants. Isotonic saline was injected contralaterally as a control. Pain intensity was assessed on a visual analog scale (VAS). Resisted hip adduction at three different angles and trunk flexion were completed before, during, and after injections. Pain provocation in the presence of experimental pain was recorded as a true positive compared with pain provocation in the non-pain conditions. Similar peak VAS scores were found after hypertonic saline injections into the AL and RF and both induced higher VAS scores than isotonic saline (P < 0.01). Adduction at 0° had the greatest positive likelihood ratio (+LR = 2.8, 95%CI: 1.09-7.32) with 45° (-LR = 0.0, 95%CI: 0.00-1.90) and 90° (-LR = 0.0, 95%CI: 0.00-0.94) having the lowest negative LR. This study indicates that the 0° hip adduction test resisted at the ankles optimizes the diagnostic procedure without compromising diagnostic capacity to identify experimental groin pain. Validation in clinical populations is warranted.