Therapeutic Photobiomodulation Before Strenuous Exercise Attenuates Shoulder Muscle Fatigue.

CONTEXT: Photobiomodulation therapy (PBMT) applied as a preconditioning treatment before exercise has been shown to attenuate fatigue and improve skeletal muscle contractile function during high-intensity resistance exercise. Practical implications for preconditioning muscle with PBMT prior to fatiguing exercise include a safe and non-invasive means to enhance performance and reduce the risk of musculoskeletal injury. OBJECTIVE: To examine the muscle fatigue attenuating effects of PBMT on performance of the shoulder external rotator muscle group when applied as a preconditioning treatment before high-intensity, high-volume resistance exercise. DESIGN: Sham-controlled, cross-over design. SETTING: Laboratory. PARTICIPANTS: Twenty healthy men (n=8) and women (n=12) between the age of 18 and 30. INTERVENTION: PBMT was administered using a near-infrared laser (λ=810/980nm, 1.8 W/cm2, treatment area = 80cm2-120 cm2) to the shoulder external rotator muscles at a radiant exposure of 10 J/cm2. Subjects performed 12 sets of isokinetic shoulder exercise. Each set consisted of 21 concentric contractions of internal and external rotation at 60°/s. The sets were subdivided into 3 blocks of exercise [Block 1: sets 1-4; Block 2: sets 5-8; Block 3: sets 9-12]. MAIN OUTCOME MEASURES: normalized peak torque [Nm/kg], average peak torque [Nm], total work [Nm], and average power [W]. RESULTS: During the last block of exercise (sets 9-12), all performance measures for the active PBMT condition were 6.2% to 10% greater than the sham PBMT values (p < 0.02 to 0.001). CONCLUSIONS: PBMT attenuated fatigue and improved muscular performance of the shoulder external rotators in the latter stages of strenuous resistance exercise.

Circulating Inflammatory Biomarkers Predict Pain Change Following Exercise-Induced Shoulder Injury: Findings From the Biopsychosocial Influence on Shoulder Pain Preclinical Trial.

Shoulder pain is a highly prevalent musculoskeletal condition that frequently leads to suboptimal clinical outcomes. This study tested the extent to which circulating inflammatory biomarkers are associated with reports of shoulder pain and upper-extremity disability for a high-risk genetic by psychological subgroup (catechol-O-methyltransferase [COMT] variation by pain catastrophizing [PCS]). Pain-free adults meeting high-risk COMT × PCS subgroup criteria completed an exercise-induced muscle injury protocol. Thirteen biomarkers were collected and analyzed from plasma 48 hours after muscle injury. Shoulder pain intensity and disability (Quick-DASH) were reported at 48 and 96 hours to calculate change scores. Using an extreme sampling technique, 88 participants were included in this analysis. After controlling for age, sex, and BMI, there were moderate positive associations between higher c-reactive protein (CRP; ߈ = .62; 95% confidence interval [CI] = -.03, 1.26), interleukin-6 (IL-6; ߈ = 3.13; CI = -.11, 6.38), and interleukin-10 (IL-10; ߈ = 2.51; CI = -.30, 5.32); and greater pain reduction from 48 to 96 hours post exercise muscle injury. Using an exploratory multivariable model to predict pain changes from 48 to 96 hours, we found participants with higher IL-10 were less likely to experience a high increase in pain (߈ = -10.77; CI = -21.25, -2.69). Study findings suggest CRP, IL-6, and IL-10 are related to shoulder pain change for a preclinical high-risk COMT × PCS subgroup. Future studies will translate to clinical shoulder pain and decipher the complex and seemingly pleiotropic interplay between inflammatory biomarkers and shoulder pain change. PERSPECTIVE: In a preclinical high-risk COMT × PCS subgroup, 3 circulating inflammatory biomarkers (CRP, IL-6, and IL-10) were moderately associated with pain improvement following exercise-induced muscle injury.

Biopsychosocial influence on shoulder pain: results from a randomized preclinical trial of exercise-induced muscle injury.

ABSTRACT: Prior cohort studies validated that a subgroup defined by a specific COMT genotype and pain catastrophizing is at increased risk for heightened responses to exercise-induced or surgically induced shoulder pain. In this clinical trial, we used our preclinical model of exercise-induced muscle injury and pain to test the efficacy of interventions matched to characteristics of this high-risk subgroup (ie, personalized medicine approach). Potential participants provided informed consent to be screened for eligibility based on subgroup membership and then, as appropriate, were enrolled into the trial. Participants (n = 261) were randomized to 1 of 4 intervention groups comprised of pharmaceutical (propranolol or placebo) and informational (general education or psychologic intervention) combinations. After muscle injury was induced, participants received randomly assigned treatment and were followed for the primary outcome of shoulder pain intensity recovery over 4 consecutive days. Recovery rates were 56.4% (placebo and psychologic intervention), 55.4% (placebo and general education), 62.9% (propranolol and psychologic intervention), and 56.1% (propranolol and general education). No statistical differences were found between intervention groups in the primary analyses. Additional analyses found no differences between these intervention groups when shoulder pain duration was an outcome, and no differential treatment responses were detected based on sex, race, or level of pain catastrophizing. This trial indicates that these treatments were not efficacious for this high-risk subgroup when shoulder pain was induced by exercise-induced muscle injury. Accordingly, this phenotype should only be used for prognostic purposes until additional trials are completed in clinical populations.

Pitching shoulder passive flexibility: torque-angle analysis for external rotation and internal rotation.

In this study, a custom device was developed to analyse the pitching shoulder's external rotation (ER) and internal rotation (IR) passive flexibility. We analysed three novel measures: the resistance onset angle (ROA = angle where the shoulder begins stretching), rotational stiffness, and torque at the end range of motion (ROM). The purpose was to conduct a bilateral analysis to determine if there are significant differences between the throwing and non-throwing shoulder. Participants were 30 upper level pitchers (13 division I, 17 minor league). During testing, pitchers laid supine on a treatment table and the arm was secured to a rotational wheel with the shoulder abducted 90° and elbow flexed 90°. Dependent t-tests revealed significant (p < 0.01) and relatively extreme bilateral differences for all three variables. The throwing shoulder had: increased ER ROA (9°), decreased IR ROA (5.3°), increased ER stiffness (17%), increased IR stiffness (34%), increased ER torque (21%), and increased IR torque (30%). Secondary correlation analysis was completed to determine if the torque-angle variables were good predictors of the end ROM. Stiffness correlations were weak for ER (r = 0.35, p = 0.048) and IR (r = 0.42, p = 0.017) but ROA correlations were strong for ER (r = 0.85, p < 0.001) and IR (r = 0.86, p < 0.001).

Sensory and Psychological Factors Predict Exercise-Induced Shoulder Injury Responses in a High-Risk Phenotype Cohort.

Our prior studies identified a high-risk phenotype (ie, high pain sensitivity variant of the catechol-O-methyltransferase gene (Single Nucleotide Polymorphism [SNP] rs6269) and pain catastrophizing scores) for shoulder pain. The current study identified sensory and psychological predictors of heightened pain responses following exercise-induced shoulder injury. Healthy participants (N = 131) with the SNP rs6269 catechol-O-methyltransferase gene and Pain Catastrophizing Scale scores ≥5 underwent baseline sensory and psychological testing followed by an established shoulder fatigue protocol, to induce muscle injury. Movement-evoked pain, pain intensity, disability, and strength were assessed 24 hours postinjury. Demographic, sensory, and psychological variables were included as predictors in full and parsimonious models for each outcome. The highest variance explained was for the shoulder disability outcome (full model R2 = .20, parsimonious R2 = .13). In parsimonious models, the individual predictors identified were: 1) 1st pulse heat pain sensitivity for isometric shoulder movement-evoked pain and pain intensity; 2) pressure pain threshold for shoulder disability; 3) fear of pain for active shoulder movement-evoked pain and shoulder disability; and 4) depressive symptoms for shoulder strength. Findings indicate specific pain sensitivity and psychological measures may have additional prognostic value for self-reported disability within a high-risk phenotype. These findings should be tested in a clinical cohort for validation. PERSPECTIVE: The current study extends previous work by providing insight regarding how poor shoulder outcomes may develop within a high-risk phenotype. Specifically, 1st pulse heat pain sensitivity and pressure pain threshold were sensory measures, and fear of pain and depressive symptoms were psychological measures, that improved prediction of different shoulder outcomes.

Plasma Concentrations of Select Inflammatory Cytokines Predicts Pain Intensity 48 Hours Post-Shoulder Muscle Injury.

OBJECTIVES: The relationship between elevated inflammatory cytokine levels and peak pain intensity following acute musculoskeletal injury has not been fully elucidated in high risk subgroups. Identifying the role that these cytokines have on pain responses may help with developing tailored therapeutic approaches. METHODS: Data were collected from 54 participants who were vulnerable to a robust pain response and delayed recovery following musculoskeletal injury. Participants completed baseline active and resting pain measurements and a blood draw before an exercised induced shoulder muscle injury. Participants returned at 24 and 48 hours postinjury for follow-up pain measurements and blood draws. Blood plasma was analyzed for interleukin (IL)-1ß, IL-6, IL-8, IL-10, and tumor necrosis factor α. Pearson bivariate correlations were performed between cytokines and pain measurements to identify candidate variables for stepwise multiple linear regression predicting pain intensity reports. RESULTS: Pearson bivariate correlation identified 13/45 correlations between inflammatory cytokines and resting pain intensity and 9/45 between inflammatory cytokines and active pain (P<0.05, r≥0.3 or r≤-0.3). This led to 5 stepwise multiple linear regression models, of which 4 met the statistical criterion (P<0.0167); including IL-10 baseline plasma concentrations predicting active pain (r=0.19) and resting pain (r=0.15) intensity 48 hours postinjury. IL-6 and IL-10 plasma concentrations at 48 hours were respectively associated with active and resting pain at 48 hours. DISCUSSION: These findings suggest that elevated concentrations of inflammatory cytokines, specifically IL-10 (at baseline and 48 h) and IL-6 (at 48 h), may play a role in heightened pain responses following exercise-induced muscle injury.

Motoneuron Function Does not Change Following Whole-Body Vibration in Individuals With Chronic Ankle Instability.

CONTEXT: Following a lateral ankle sprain, ∼40% of individuals develop chronic ankle instability (CAI), characterized by recurrent injury and sensations of giving way. Deafferentation due to mechanoreceptor damage postinjury is suggested to contribute to arthrogenic muscle inhibition (AMI). Whole-body vibration (WBV) has the potential to address the neurophysiologic deficits accompanied by CAI and, therefore, possibly prevent reinjury. OBJECTIVE: To determine if an acute bout of WBV can improve AMI and proprioception in individuals with CAI. DESIGN AND PARTICIPANTS: The authors examined if an acute bout of WBV can improve AMI and proprioception in individuals with CAI with a repeated-measures design. A total of 10 young adults with CAI and 10 age-matched healthy controls underwent a control, sham, and WBV condition in randomized order. SETTING: Biomechanics laboratory. INTERVENTION: WBV. MAIN OUTCOME MEASURES: Motoneuron pool recruitment was assessed via Hoffmann reflex (H-reflex) in the soleus. Proprioception was evaluated using ankle joint position sense at 15° and 20° of inversion. Both were assessed prior to, immediately following, and 30 minutes after the intervention (pretest, posttest, and 30mPost, respectively). RESULTS: Soleus maximum H-reflex:M-response (H:M) ratios were 25% lower in the CAI group compared with the control group (P = .03). Joint position sense mean constant error did not differ between groups (P = .45). Error at 15° in the CAI (pretest 0.8 [1.6], posttest 2.0 [2.8], 30mPost 2.0 [1.9]) and control group (pretest 0.8 [2.0], posttest 0.6 [2.9], 30mPost 0.5 [2.1]) did not improve post-WBV. Error at 20° did not change post-WBV in the CAI (pretest 1.3 [1.7], posttest 1.0 [2.4], 30mPost 1.5 [2.2]) or control group (pretest -0.3 [3.0], posttest 0.8 [2.1], 30mPost 0.6 [1.8]). CONCLUSION: AMI is present in the involved limb of individuals with CAI. The acute response following a single bout of WBV did not ameliorate the presence of AMI nor improve proprioception in those with CAI.

Genetic and psychological factors interact to predict physical impairment phenotypes following exercise-induced shoulder injury.

BACKGROUND: We investigated interactions between genetic and psychological factors in predicting shoulder impairment phenotypes. We hypothesized that pro-inflammatory genes would display stronger relationships compared with pain-related genes when combined with psychological factors for predicting phenotypic changes. SUBJECTS AND METHODS: Altogether, 190 participants completed a 5-day experimental protocol. An experimental shoulder injury model was used to induce physical impairment, and a priori selected genetic (pain-related, pro-inflammatory) and psychological (anxiety, depressive symptoms, pain catastrophizing, fear of pain, kinesiophobia) factors were included as predictors of interest. Impairment phenotypes were injury-induced deficits in range of motion (ROM) and strength. After controlling for age, sex, and race, genetic and psychological predictors were entered separately as main effects and interaction terms in regression models for each phenotype. RESULTS: Strong statistical evidence was provided for interactions between: 1) IL-1ß (rs1143634) and fear of pain for predicting loss of shoulder flexion and abduction, 2) IL-1ß (rs1143634) and anxiety for predicting loss of flexion, and 3) IL-1ß (rs1143634) and depressive symptoms for predicting loss of internal rotation. In addition, the interaction between OPRM1 (rs1799971) and fear of pain as well as COMT (rs4818) and pain catastrophizing provided strong statistical evidence for predicting strength loss. CONCLUSION: Pro-inflammatory gene variants contributed more to physical impairment with two single nucleotide polymorphisms (SNPs; IL-1ß [rs1143634] and TNF/LTA [rs2229094]) interacting with psychological factors to predict six shoulder impairment phenotypes. In comparison, two pain-related gene SNPs (OPRM1 [rs1799971] and COMT [rs4818]) interacted with psychological factors to predict four shoulder impairment phenotypes (abduction: 5-day average loss; strength loss: 5-day average, peak, and relative loss).

Developing reliable measures of the passive torque-angle relationship for shoulder internal and external rotation: Implications for overhead athletics.

OBJECTIVES: 1) Thoroughly assess shoulder flexibility by establishing the passive torque-angle relationship for internal and external rotation with the arm in an overhead athletics position (abducted 90°) and 2) test the reliability of four passive torque-angle measures. DESIGN: Reliability study. SETTING: Data were collected in a university biomechanics laboratory. PARTICIPANTS: Bilateral shoulder flexibility of 15 male college students (20.7 ±â€¯1.1 y) was evaluated twice in two sessions over 7-10 days. MAIN OUTCOME MEASURES: For both ER and IR, reliability was assessed bilaterally (intra-session, inter-session, and inter-tester) for the traditional range of motion measure and three novel kinetic measures: torque at end ROM, resistance onset angle, rotational stiffness. This resulted in 48 total assessments. RESULTS: Thirty-four assessments had good to excellent reliability (ICC ≥ 0.8), 10 had fair reliability (0.7 ≤ ICC < 0.8), and 4 had poor reliability (ICC< 0.7). Three of the four flexibility measures had a good overall ICC score: ROM (0.83), torque at end ROM (0.84), and resistance onset angle (0.81). The fourth, stiffness, had a fair overall reliability score (0.74). CONCLUSIONS: The passive torque-angle measures should be assimilated into clinical and research settings to determine the relevance to injury, rehabilitation, and performance.

Prolonged Reduction in Shoulder Strength after Transcutaneous Electrical Nerve Stimulation Treatment of Exercise-Induced Acute Muscle Pain.

OBJECTIVES: Transcutaneous electrical nerve stimulation (TENS) is commonly used for reducing musculoskeletal pain to improve function. However, peripheral nerve stimulation using TENS can alter muscle motor output. Few studies examine motor outcomes following TENS in a human pain model. Therefore, this study investigated the influence of TENS sensory stimulation primarily on motor output (strength) and secondarily on pain and disability following exercise-induced delayed-onset muscle soreness (DOMS). METHODS: Thirty-six participants were randomized to a TENS treatment, TENS placebo, or control group after completing a standardized DOMS protocol. Measures included shoulder strength, pain, mechanical pain sensitivity, and disability. TENS treatment and TENS placebo groups received 90 minutes of active or sham treatment 24, 48, and 72 hours post-DOMS. All participants were assessed daily. RESULTS: A repeated measures analysis of variance and post-hoc analysis indicated that, compared to the control group, strength remained reduced in the TENS treatment group (48 hours post-DOMS, P < 0.05) and TENS placebo group (48 hours post-DOMS, P < 0.05; 72 hours post-DOMS, P < 0.05). A mixed-linear modeling analysis was conducted to examine the strength (motor) change. Randomization group explained 5.6% of between-subject strength variance (P < 0.05). Independent of randomization group, pain explained 8.9% of within-subject strength variance and disability explained 3.3% of between-subject strength variance (both P < 0.05). DISCUSSION: While active and placebo TENS resulted in prolonged strength inhibition, the results were nonsignificant for pain. Results indicated that higher pain and higher disability were independently related to decreased strength. Regardless of the impact on pain, TENS, or even the perception of TENS, may act as a nocebo for motor output.

Expectancy Reduces Symptoms but not Functional Impairment Following Exercise-induced Musculoskeletal Injury.

OBJECTIVES: To quantify the extent to which the participant-provider interaction influences the response to sham treatment following exercised-induced acute musculoskeletal pain. MATERIALS AND METHODS: In total, 40 participants between the ages of 18 and 35 volunteered for the study. Participants came to the laboratory for 3 test sessions 48-hour apart (day 1, 3, and 5). During the initial session, baseline measures were assessed and participants underwent a fatigue protocol for the biceps brachii. Participants were then assigned to a positive expectation or a no-expectation condition before receiving a sham laser therapy treatment. The positive expectation group received symptom improvement priming before their sham treatment. Participants allocated to the no-expectation condition received no feedback before the sham treatment. Maximum voluntary isometric contraction; relaxed elbow angle; visual analog scale; and the QuickDash questionnaire were used as outcome measures. RESULTS: The positive expectation group had a significant reduction in perceived pain compared with the no-expectation group at day 3 follow-up, with the mean scores being 34.65 mm (SE=4.44) compared with 49.4 mm (SE=5.79), respectively. There were no between-group differences with respect to maximum voluntary isometric contraction, QuickDash, or relaxed elbow angle outcomes. In addition, there were no significant between-group differences observed with expected pain on follow-up visits, the effect sizes were d=0.26 on day 1 for day 3 and d=0.51 on day for day 5. DISCUSSION: Positive expectations before a sham treatment enhanced reduction in pain intensity but did not improve functional impairments following exercise-induced acute musculoskeletal injury.

Biopsychosocial influence on shoulder pain: Rationale and protocol for a pre-clinical trial.

BACKGROUND: Chronic musculoskeletal pain conditions are a prevalent and disabling problem. Preventing chronic musculoskeletal pain requires multifactorial treatment approaches that address its complex etiology. Prior cohort studies identified a high risk subgroup comprised of variation in COMT genotype and pain catastrophizing. This subgroup had increased chance of heightened pain responses (in a pre-clinical model) and higher 12month post-operatives pain intensity ratings (in a clinical model). This pre-clinical trial will test mechanisms and efficacy of personalized pain interventions matched to the genetic and psychological characteristics of the high-risk subgroup. METHODS: Potential participants will be screened for high risk subgroup membership, appropriateness for exercise-induced muscle injury protocol, and appropriateness for propranolol administration. Eligible participants that consent to the study will then be randomized into one of four treatment groups; 1) personalized pharmaceutical and psychological education; 2) personalized pharmaceutical and general education; 3) placebo pharmaceutical and psychological education; 4) placebo pharmaceutical and psychological education. Over the 5-day study period participants will complete an exercise-induced muscle injury protocol and receive study interventions. Pain and disability assessments will be completed daily, with primary outcomes being duration of shoulder pain (number of days until recovery), peak shoulder pain intensity, and peak shoulder disability. Secondary outcomes include inflammatory markers, psychological mediators, and measures of pain sensitivity regulation. CONCLUSION: This pre-clinical trial builds on prior cohort studies and its completion will provide foundational data supporting efficacy and mechanisms of personalized interventions for individuals that may be at increased risk for developing chronic shoulder pain. TRIAL REGISTRATION: ClinicalTrials.gov registry, NCT02620579 (Registered on November 13, 2015).

Photobiomodulation delays the onset of skeletal muscle fatigue in a dose-dependent manner.

Photobiomodulation (PBM) therapy has been implicated as an effective ergogenic aid to delay the onset of muscle fatigue. The purpose of this study was to examine the dose-response ergogenic properties of PBM therapy and its ability to prolong time to task failure by enhancing muscle activity and delaying the onset of muscle fatigue using a static positioning task. Nine participants (24.3 ± 4.9 years) received three doses of near-infrared (NIR) light therapy randomly on three separate sessions (sham, 240, and 480 J). For the positioning task, participants held a 30 % one-repetition maximum (1-RM) load using the index finger until volitional fatigue. Surface electromyography (sEMG) of the first dorsal interosseous muscle was recorded for the length of the positioning task. Outcomes included time to task failure (TTF), muscle fatigue, movement accuracy, motor output variability, and muscle activity (sEMG). The 240-J dose significantly extended TTF by 26 % (p = 0.032) compared with the sham dose. TTF for the 240-J dose was strongly associated with a decrease in muscle fatigue (R (2) = 0.54, p = 0.024). Our findings show that a 240-J dose of NIR light therapy is efficacious in delaying the onset and extent of muscle fatigue during submaximal isometric positioning tasks. Our findings suggest that NIR light therapy may be used as an ergogenic aid during functional tasks or post-injury rehabilitation.

Range of motion as a predictor of clinical shoulder pain during recovery from delayed-onset muscle soreness.

CONTEXT: Athletic trainers use clinical pain and range of motion (ROM) to gauge recovery after musculoskeletal injury. Limited evidence to date suggests which shoulder ROM measures can predict symptomatic relief and functional recovery after delayed-onset muscle soreness (DOMS). OBJECTIVE: To determine whether shoulder passive internal rotation, passive external rotation, active abduction, and active flexion and evoked pain with abduction are associated with resting pain experienced after exercise-induced DOMS. DESIGN: Descriptive laboratory study. SETTING: Controlled research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 110 healthy, right-hand-dominant participants (44 men: age = 25.39 ± 7.00 years, height = 178.93 ± 7.01 cm, weight = 78.59 ± 14.04 kg; 66 women: age = 22.98 ± 6.11 years, height = 164.64 ± 6.94 cm, weight = 61.86 ± 11.67 kg). INTERVENTION(S): Participants completed an exercise-induced DOMS protocol for the external rotators of the dominant shoulder to replicate muscle injury. MAIN OUTCOME MEASURE(S): Current resting pain was assessed daily for 96 hours using the Brief Pain Inventory. We evaluated functional recovery with measures of ROM in abduction, internal rotation, external rotation, and flexion. Evoked pain with active abduction was reported, and the pain rating served as the dependent variable in the regression model. RESULTS: Impairment measures explained resting pain at 48 (R2 = 0.392) and 96 hours (R2 = 0.164). Abduction and internal-rotation ROM and evoked pain with abduction predicted resting pain at 48 hours (P < .001). At 96 hours, evoked pain with abduction of the injured arm (P < .001) was the significant contributor to resting pain. CONCLUSIONS: These models suggest that resting pain after experimentally induced DOMS occurs at 48 hours and is associated with specific ranges of motion and evoked pain with abduction.

Biopsychosocial influence on shoulder pain: risk subgroups translated across preclinical and clinical prospective cohorts.

Tailored treatment based on individual risk factors is an area with promise to improve options for pain relief. Musculoskeletal pain has a biopsychosocial nature, and multiple factors should be considered when determining risk for chronic pain. This study investigated whether subgroups comprised genetic and psychological factors predicted outcomes in preclinical and clinical models of shoulder pain. Classification and regression tree analysis was performed for an exercise-induced shoulder injury cohort (n = 190) to identify high-risk subgroups, and a surgical pain cohort (n = 150) was used for risk validation. Questionnaires for fear of pain and pain catastrophizing were administered before injury and preoperatively. DNA collected from saliva was genotyped for a priori selected genes involved with pain modulation (COMT and AVPR1A) and inflammation (IL1B and TNF/LTA). Recovery was operationalized as a brief pain inventory rating of 0/10 for current pain intensity and <2/10 for worst pain intensity. Follow-up for the preclinical cohort was in daily increments, whereas follow-up for the clinical cohort was at 3, 6, and 12 months postoperatively. Risk subgroups comprised the COMT high pain sensitivity variant and either pain catastrophizing or fear of pain were predictive of heightened shoulder pain responses in the preclinical model. Further analysis in the clinical model identified the COMT high pain sensitivity variant and pain catastrophizing subgroup as the better predictor. Future studies will determine whether these findings can be replicated in other anatomical regions and whether personalized medicine strategies can be developed for this risk subgroup.

Near-infrared light therapy to attenuate strength loss after strenuous resistance exercise.

CONTEXT: Near-infrared (NIR) light therapy is purported to act as an ergogenic aid by enhancing the contractile function of skeletal muscle. Improving muscle function is a new avenue for research in the area of laser therapy; however, very few researchers have examined the ergogenic effects of NIR light therapy and the influence it may have on the recovery process during rehabilitation. OBJECTIVE: To evaluate the ergogenic effect of NIR light therapy on skeletal muscle function. DESIGN: Crossover study. SETTING: Controlled laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-nine healthy men (n = 21) and women (n = 18; age = 20.0 ± 0.2 years, height = 169 ± 2 cm, mass = 68.4 ± 1.8 kg, body mass index = 23.8 ± 0.4 kg/m(2)). INTERVENTION(S): Each participant received active and sham treatments on the biceps brachii muscle on 2 separate days. The order of treatment was randomized. A class 4 laser with a cumulative dose of 360 J was used for the active treatment. After receiving the treatment on each day, participants completed an elbow-flexion resistance-exercise protocol. MAIN OUTCOME MEASURE(S): The dependent variables were elbow range of motion, muscle point tenderness, and strength (peak torque). Analysis of variance with repeated measures was used to assess changes in these measures between treatments at baseline and at follow-up, 48 hours postexercise. Additionally, immediate strength loss postexercise was compared between treatments using a paired t test. RESULTS: Preexercise to postexercise strength loss for the active laser treatment, although small, was less than with the sham treatment (P = .05). CONCLUSIONS: Applied to skeletal muscle before resistance exercise, NIR light therapy effectively attenuated strength loss. Therefore, NIR light therapy may be a beneficial, noninvasive modality for improving muscle function during rehabilitation after musculoskeletal injury. However, future studies using higher treatment doses are warranted.

Suprathreshold heat pain response predicts activity-related pain, but not rest-related pain, in an exercise-induced injury model.

Exercise-induced injury models are advantageous for studying pain since the onset of pain is controlled and both pre-injury and post-injury factors can be utilized as explanatory variables or predictors. In these studies, rest-related pain is often considered the primary dependent variable or outcome, as opposed to a measure of activity-related pain. Additionally, few studies include pain sensitivity measures as predictors. In this study, we examined the influence of pre-injury and post-injury factors, including pain sensitivity, for induced rest and activity-related pain following exercise induced muscle injury. The overall goal of this investigation was to determine if there were convergent or divergent predictors of rest and activity-related pain. One hundred forty-three participants provided demographic, psychological, and pain sensitivity information and underwent a standard fatigue trial of resistance exercise to induce injury of the dominant shoulder. Pain at rest and during active and resisted shoulder motion were measured at 48- and 96-hours post-injury. Separate hierarchical models were generated for assessing the influence of pre-injury and post-injury factors on 48- and 96-hour rest-related and activity-related pain. Overall, we did not find a universal predictor of pain across all models. However, pre-injury and post-injury suprathreshold heat pain response (SHPR), a pain sensitivity measure, was a consistent predictor of activity-related pain, even after controlling for known psychological factors. These results suggest there is differential prediction of pain. A measure of pain sensitivity such as SHPR appears more influential for activity-related pain, but not rest-related pain, and may reflect different underlying processes involved during pain appraisal.

Inflammatory genes and psychological factors predict induced shoulder pain phenotype.

PURPOSE: The pain experience has multiple influences, but little is known about how specific biological and psychological factors interact to influence pain responses. The current study investigated the combined influences of genetic (pro-inflammatory) and psychological factors on several preclinical shoulder pain phenotypes. METHODS: An exercise-induced shoulder injury model was used, and a priori selected genetic (IL1B, TNF/LTA region, and IL6 single nucleotide polymorphisms (SNP)) and psychological (anxiety, depression symptoms, pain catastrophizing, fear of pain, and kinesiophobia) factors were included as the predictors of interest. The phenotypes were pain intensity (5-d average and peak reported on numerical rating scale), upper extremity disability (5-d average and peak reported on the Quick Disabilities of the Arm, Shoulder and Hand instrument), and duration of shoulder pain (d). RESULTS: After controlling for age, sex, and race, the genetic and psychological predictors were entered separately as main effects and interaction terms in regression models for each pain phenotype. Results from the recruited cohort (n = 190) indicated strong statistical evidence for the interactions between 1) TNF/LTA SNP rs2229094 and depression symptoms for average pain intensity and duration and 2) IL1B two SNP diplotype and kinesiophobia for average shoulder pain intensity. Moderate statistical evidence for prediction of additional shoulder pain phenotypes included interactions of kinesiophobia, fear of pain, or depressive symptoms with TNF/LTA rs2229094 and IL1B. CONCLUSIONS: These findings support the combined predictive ability of specific genetic and psychological factors for shoulder pain phenotypes by revealing novel combinations that may merit further investigation in clinical cohorts to determine their involvement in the transition from acute to chronic pain conditions.

Biopsychosocial influence on exercise-induced injury: genetic and psychological combinations are predictive of shoulder pain phenotypes.

UNLABELLED: Chronic pain is influenced by biological, psychological, social, and cultural factors. The current study investigated potential roles for combinations of genetic and psychological factors in the development and/or maintenance of chronic musculoskeletal pain. An exercise-induced shoulder injury model was used, and a priori selected genetic (ADRB2, COMT, OPRM1, AVPR1 A, GCH1, and KCNS1) and psychological (anxiety, depressive symptoms, pain catastrophizing, fear of pain, and kinesiophobia) factors were included as predictors. Pain phenotypes were shoulder pain intensity (5-day average and peak reported on numerical rating scale), upper extremity disability (5-day average and peak reported on the QuickDASH), and shoulder pain duration (in days). After controlling for age, sex, and race, the genetic and psychological predictors were entered as main effects and interaction terms in separate regression models for the different pain phenotypes. Results from the recruited cohort (N = 190) indicated strong statistical evidence for interactions between the COMT diplotype and 1) pain catastrophizing for 5-day average upper extremity disability and 2) depressive symptoms for pain duration. There was moderate statistical evidence for interactions for other shoulder pain phenotypes between additional genes (ADRB2, AVPR1 A, and KCNS1) and depressive symptoms, pain catastrophizing, or kinesiophobia. These findings confirm the importance of the combined predictive ability of COMT with psychological distress and reveal other novel combinations of genetic and psychological factors that may merit additional investigation in other pain cohorts. PERSPECTIVE: Interactions between genetic and psychological factors were investigated as predictors of different exercise-induced shoulder pain phenotypes. The strongest statistical evidence was for interactions between the COMT diplotype and pain catastrophizing (for upper extremity disability) or depressive symptoms (for pain duration). Other novel genetic and psychological combinations were identified that may merit further investigation.

Effect of near-infrared light exposure on mitochondrial signaling in C2C12 muscle cells.

Near-infrared (NIR) light is a complementary therapy used to treat musculoskeletal injuries but the underlying mechanisms are unclear. Acute NIR light treatment (~800-950 nm; 22.8 J/cm(2)) induced a dose-dependent increase in mitochondrial signaling (AMPK, p38 MAPK) in differentiated muscle cells. Repeated NIR light exposure (4 days) appeared to elevate oxidative stress and increase the upstream mitochondrial regulatory proteins AMPK (3.1-fold), p38 (2.8-fold), PGC-1α (19.7%), Sirt1 (26.8%), and reduced RIP140 (23.2%), but downstream mitochondrial regulation/content (Tfam, NRF-1, Sirt3, cytochrome c, ETC subunits) was unaltered. Our data indicates that NIR light alters mitochondrial biogenesis signaling and may represent a mechanistic link to the clinical benefits.