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).

Epidemiology of musculoskeletal injuries sustained by Naval Special Forces Operators and students.

OBJECTIVES: The aim of this analysis was to describe the incidence and common types of medical chart-reviewed musculoskeletal injuries, among four distinct groups of Naval Special Warfare (NSW) personnel: Sea, Air, and Land (SEAL) Operators, SEAL Qualification Training (SQT) students, Special Warfare Combatant-craft Crewman (SWCC) Operators, and Crewman Qualification Training (CQT) students. DESIGN: Descriptive cross-sectional study. METHODS: Medical records were reviewed for 920 NSW personnel. MSI were described and classified by frequency and incidence; anatomic location; injury type and cause; activity during injury; and potential for prevention. RESULTS: The frequency of MSI was 23.1, 46.5, 31.6, and 17.0 per 100 participants per year among SEAL, SQT, SWCC, and CQT, respectively. Upper extremity MSI were the most common in SEAL, lower extremity MSI were common in the other groups. The most frequent MSI anatomic sub-locations varied across groups (SEAL: shoulder, 21.6% of MSI; SQT: foot and toes, 17.0%; SWCC: lumbopelvic spine, 21.7%; and CQT: knee, 30.3%). Pain/spasm/ache were the most common MSI type in SEAL (29.7%) and SWCC (21.7%), tendonitis/tenosynovitis/tendinopathy was the most common MSI type in SQT (21.0%), and tendonitis/tenosynovitis/tendinopathy and fracture were the most common in CQT (15.2% each). A considerable proportion of MSI were classified as potentially preventable-SEAL: 35.1%, SQT: 53.0%, SWCC: 36.7%, and CQT: 21.2%. CONCLUSIONS: MSI cause considerable morbidity among NSW Operators and students, with distinct patterns of distribution by anatomic location and injury type. Since many injuries may be preventable, targeted interventions may be able to mitigate MSI risk.

Normative Data for the NeuroCom Sensory Organization Test in US Military Special Operations Forces.

CONTEXT: Postural stability is the ability to control the center of mass in relation to a person's base of support and can be affected by both musculoskeletal injury and traumatic brain injury. The NeuroCom Sensory Organization Test (SOT) can be used to objectively quantify impairments to postural stability. The ability of postural stability to predict injury and be used as an acute injury-evaluation tool makes it essential to the screening and rehabilitation process. To our knowledge, no published normative data for the SOT from a healthy, highly active population are available for use as a reference for clinical decision making. OBJECTIVE: To present a normative database of SOT scores from a US Military Special Operations population that can be used for future comparison. DESIGN: Cross-sectional study. SETTING: Human performance research laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 542 active military operators from Naval Special Warfare Combatant-Craft Crewmen (n = 149), Naval Special Warfare Command, Sea, Air, and Land (n = 101), US Army Special Operations Command (n = 171), and Air Force Special Operations Command (n = 121). MAIN OUTCOME MEASURE(S): Participants performed each of the 6 SOT conditions 3 times. Scores for each condition, total equilibrium composite score, and ratio scores for the somatosensory, visual, and vestibular systems were recorded. RESULTS: Differences were present across all groups for SOT conditions 1 (P < .001), 2 (P = .001), 4 (P > .001), 5 (P > .001), and 6 (P = .001) and total equilibrium composite (P = .000), visual (P > .001), vestibular (P = .002), and preference (P > .001) NeuroCom scores. CONCLUSIONS: Statistical differences were evident in the distribution of postural stability across US Special Operations Forces personnel. This normative database for postural stability, as assessed by the NeuroCom SOT, can provide context when clinicians assess a Special Operations Forces population or any other groups that maintain a high level of conditioning and training.

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.

Residual Impact of Previous Injury on Musculoskeletal Characteristics in Special Forces Operators.

BACKGROUND: Musculoskeletal injuries are a significant burden to United States Army Special Operations Forces. The advanced tactical skill level and physical training required of Army Special Operators highlights the need to optimize musculoskeletal characteristics to reduce the likelihood of suffering a recurrent injury. PURPOSE: To identify the residual impact of previous injury on musculoskeletal characteristics. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Isokinetic strength of the knee, shoulder, and back and flexibility of the shoulder and hamstrings were assessed as part of a comprehensive human performance protocol, and self-reported musculoskeletal injury history was obtained. Subjects were stratified based on previous history of low back, knee, or shoulder injury, and within-group and between-group comparisons were made for musculoskeletal variables. RESULTS: Knee injury analysis showed no significant strength or flexibility differences. Shoulder injury analysis found internal rotation strength of the healthy subjects (H) was significantly higher compared with injured (I) and uninjured (U) limbs of the injured group (H, 60.8 ± 11.5 percent body weight [%BW]; I, 54.5 ± 10.5 %BW; U, 55.5 ± 11.3 %BW) (P = .014 [H vs I] and P = .05 [H vs U]). The external rotation/internal rotation strength ratio was significantly lower in the healthy subjects compared with injured and uninjured limbs of the injured group (H, 0.653 ± 0.122; I, 0.724 ± 0.121; U, 0.724 ± 0.124) (P = .026 [H vs I] and P = .018 [H vs U]). Posterior shoulder tightness was significantly different between the injured and uninjured limb of the injured group (I, 111.6° ± 9.4°; U, 114.4° ± 9.3°; P = .008). The back injury analysis found no significant strength differences between the healthy and injured groups. CONCLUSION: Few physical differences existed between operators with prior knee or back injury. However, operators with a previous history of shoulder injury demonstrated significantly less shoulder strength than uninjured operators as well as decreased shoulder flexibility on the injured side. All operators, regardless of prior injury, must perform the same tasks; therefore, a targeted injury rehabilitation/human performance training specifically focused on internal rotation strength and tightness of the posterior capsule may help reduce the risk for recurrence of injury. Operators presenting with musculoskeletal asymmetries and/or insufficient strength ratios may be predisposed to musculoskeletal injury. CLINICAL RELEVANCE: Specific fitness programs to compensate for deficiencies in strength and flexibility need to be designed that may reduce the risk of injuries in Special Forces Operators.

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.

Pain-related fear and catastrophizing predict pain intensity and disability independently using an induced muscle injury model.

UNLABELLED: Timing of assessment of psychological construct is controversial and results differ based on the model of pain induction. Previous studies have not used an exercise-induced injury model to investigate timing of psychological assessment. Exercise-induced injury models may be appropriate for these investigations because they approximate clinical pain conditions better than other experimental stimuli. In this study we examined the changes of psychological constructs over time and determined whether timing of assessment affected the construct's association with reports of pain intensity and disability. One-hundred twenty-six healthy volunteers completed the Fear of Pain Questionnaire (FPQ-III), Pain Catastrophizing Scale (PCS), and Tampa Scale of Kinesiophobia (TSK) prior to inducing muscle injury to the shoulder. The PCS and TSK were measured again 48 and 96 hours postinjury induction. Pain intensity and disability were collected at 48 and 96 hours and served as dependent variables in separate regression models. Results indicated that the FPQ-III had the strongest prediction of pain intensity from baseline to 96 hours. After baseline the PCS and TSK were stronger predictors of pain intensity and disability, respectively. These data provide support for the use of psychological constructs in predicting outcomes from shoulder pain. However, they deviate from the current theoretical model indicating that fear of pain is a consequence of injury and instead suggests that fear of pain before injury may influence reports of pain intensity. PERSPECTIVE: The current study provides evidence that fear of pain can be assessed prior to injury. Furthermore, it supports that after injury pain catastrophizing and kinesiophobia are independently associated with pain and disability. Overall these data suggest that timing of psychological assessment may be an important consideration in clinical environments.

Symptomatic and functional responses to concentric-eccentric isokinetic versus eccentric-only isotonic exercise.

CONTEXT: Rehabilitation protocols involving eccentric resistance exercise performed with loading more than 100% concentric 1-repetition maximum are effective in increasing muscle function in both healthy and injured populations. The mode of eccentric exercise (isokinetic versus isotonic) may be an important factor in limiting symptoms of delayed-onset muscle soreness and in improving muscle function after training. OBJECTIVE: To compare functional and symptomatic responses after an eccentric-only (ECC) isotonic exercise protocol and after a combined concentric-eccentric (CON-ECC) isokinetic exercise protocol matched for total exercise volume. DESIGN: Observational study. SETTING: Controlled research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-four healthy, untrained, college-aged men (n = 12) and women (n = 12). INTERVENTION(S): Participants were randomly assigned to the ECC isotonic or CON-ECC isokinetic exercise group and performed a single bout of resistance exercise involving the elbow flexors. MAIN OUTCOME MEASURE(S): Measurements of elbow flexion and extension, isometric strength, and muscle point tenderness were obtained before exercise (baseline) and during follow-up sessions (days 2, 4, 7, and 14). Separate 1-way analyses of variance and repeated-measures analyses of variance were used to determine outcome differences. Tukey post hoc testing was performed when indicated. RESULTS: At baseline, no differences were present between groups for any measure. The ECC isotonic exercise protocol resulted in a 30% to 36% deficit in muscle strength, a 5% to 7% reduction in elbow flexion, and a 6% to 8% reduction in elbow extension at follow-up days 2 and 4 (P < .01). The CON-ECC isokinetic exercise protocol did not alter muscle strength or range of motion at any time when compared with baseline. Muscle point tenderness increased from baseline on days 2 and 4 in both groups (P < .05) but was not different between groups throughout the recovery period. CONCLUSIONS: Our results indicated more pronounced functional deficits occurred after a single bout of ECC isotonic exercise than with a CON-ECC isokinetic exercise protocol matched for training volume.

The effects of short-term alpha-ketoisocaproic acid supplementation on exercise performance: a randomized controlled trial.

BACKGROUND: This study examined the efficacy of short-term alpha-ketoisocaproic acid (KIC) monotherapy supplementation immediately prior to moderate- and high-intensity single bout exercise performance. METHODS: Thirteen resistance trained men (22.8 +/- 2.5 years; 81.6 +/- 12.6 kg) participated in a prospective, randomized, double blind, placebo controlled crossover experiment. Each subject completed one familiarization and four experimental trials with either 1.5 g or 9.0 g of either KIC or isocaloric placebo control (CONT), following an overnight fast. During the experimental trials, subjects consumed the supplement regimen and then completed leg and chest press repetitions to failure and 30 s of repeated maximal vertical jumping (VJ) on a force plate. RESULTS: In this treatment regimen, no significant differences (p > 0.05) were observed between dosages or conditions for leg press (low CONT = 19.8 +/- 0.4 SEM, low KIC = 21.0 +/- 0.5, high CONT = 20.1 +/- 0.3, high KIC = 22.4 +/- 0.6) or chest press (low CONT = 18.1 +/- 0.2, low KIC = 18.5 +/- 0.3, high CONT = 17.8 +/- 0.3, high KIC = 18.0 +/- 0.3) repetitions to failure. Additionally, no significant differences were observed for peak or mean VJ performance (low CONT = 34.6 +/- 2.2 cm and 28.6 +/- 1.8 cm; low KIC = 35.6 +/- 2.0 cm and 29.4 +/- 1.6 cm; high CONT = 35.7 +/- 2.1 cm and 29.4 +/- 1.7 cm; high KIC = 34.8 +/- 2.3 cm and 28.3 +/- 1.7 cm), respectively. CONCLUSION: Based on our results, we conclude that acute KIC ingestion by itself with no other ergogenic supplement, immediately prior to exercise, did not alter moderate- nor high-intensity single-bout exercise performance in young resistance-trained males. This study addressed single-dose single-bout performance events; the efficacy of KIC monotherapy supplementation on repeated high-intensity exercise bouts and long-term exercise training remains unknown.