Hydrodynamic Flow Characteristics of a Recirculating Pool: Examining the Ecological Validity for Training and Testing.

ABSTRACT: Krajewski, KT, Beethe, AZ, Dever, DE, Johnson, CD, Nindl, BC, Lovalekar, MT, Flanagan, SD, and Connaboy, C. Hydrodynamic flow characteristics of a recirculating pool: examining the ecological validity for training and testing. J Strength Cond Res 37(10): 2023-2031, 2023-Recirculating swimming flumes (RSFs) with elliptical multifeature designs have grown in popularity due to their multifunctionality for rehabilitation and training. Because of their smaller footprint, laboratories have adopted their use to investigate swimming and underwater treadmill running. However, little is known about the hydrodynamic characteristics of these RSFs and how they might influence outcomes. The purpose was to determine hydrodynamic flow characteristics of an RSF at the manufacturers' set "speeds" around the centroid of flow projection. Hydrodynamic velocity profiles were collected through a 3D profiling velocimeter, sampling at 200 Hz in an RSF. Data were collected 0.5 and 1.5 m from the projection channel at designated flume "speeds" of 30-95 (+99) in 5-unit increments. Velocity data were collected for 1 minute per trial (location × speed) to determine mean flow velocity (MFV) for 10, 20, 30, and 40 cm2 cross-sectional areas (CSAs). A two-way ANOVA was conducted comparing CSAs from the surface by distance from the current channel (4 × 2). Separate ANOVAs were conducted to assess differences in MFV across each CSA. Significant differences between flow CSAs indicated that MFV is less for a larger area at the same speed, indicative of variable and turbulent flow characteristics across the respective CSAs. Mean flow velocity was further diminished by distance from the flow channel as supported by the main effect, thus exposing an individual to variant flow velocities simultaneously. Limited stability of the flow velocity centroid could affect swim mechanics making the movement pattern no longer analogous to traditional pool and open water swimming, rather resembling swimming upstream in a river with turbulent flow.

Prevention of Lower Extremity Musculoskeletal Injuries in Tactical and First Responder Populations: A Systematic Review and Meta-Analysis of Randomized Trials From 1955 to 2020.

ABSTRACT: Sinnott, AM, Krajewski, KT, LaGoy, AD, Beckner, ME, Proessl, F, Canino, MC, Nindl, BC, Turner, RL, Lovalekar, MT, Connaboy, C, and Flanagan, SD. Prevention of lower extremity musculoskeletal injuries in tactical and first responder populations: A systematic review and meta-analysis of randomized trials from 1955 to 2020. J Strength Cond Res 37(1): 239-252, 2023-Lower extremity musculoskeletal injuries (LEMSIs) impose a significant burden on tactical and first responder populations. To determine the effectiveness of LEMSI prevention strategies, we performed a systematic review and meta-analysis of randomized controlled trials published in English from 1955 to 2020 (PROSPERO: CRD42018081799). MEDLINE, EMBASE, Cochrane, CINAHL, ProQuest, and DTIC databases were searched for trials that assigned military service members, police, firefighters, or paramedics to LEMSI prevention interventions with a minimum surveillance period of 12 weeks. Evidence was synthesized as odds ratios (OR) for LEMSI occurrence between individuals assigned to interventions and those assigned to standard activities. Risk of bias was assessed with the Cochrane Risk of Bias tool 2.0. Random-effects meta-analyses were conducted for (a) physical training and (b) footwear modifications to reduce LEMSI and (c) footwear modifications to reduce stress fractures specifically. Certainty in the body of evidence was determined with the GRADE approach. Of 28,499 records, 18 trials comprised of more than 11,000 subjects were synthesized. Interventions included physical training (8, N = 6,838), footwear modifications (8, N = 3,792), nutritional supplementation (1, N = 324), and training modifications (1, N = 350). Overall risk of bias was generally moderate ( N = 7 of 18) or high ( N = 9 of 18). Physical training (OR = 0.87, 95% CI [0.71, 1.08], p = 0.22, I 2 = 58.4%) and footwear modification (OR = 1.13, 95% CI [0.85, 1.49], p = 0.42, I 2 = 0.0%) did not reduce LEMSI or stress fractures (OR = 0.76, 95% CI [0.45, 1.28], p = 0.30, I 2 = 70.7%). Our results indicate that there is weak evidence to support current LEMSI prevention strategies. Future efforts will benefit from longer surveillance periods, assessment of women and nonmilitary populations, improved methodological rigor, and a greater breadth of approaches.

Compromised Dynamic Postural Stability Under Increased Load Carriage Magnitudes.

Warfighter performance may be compromised through the impact of load carriage on dynamic postural stability. Men and women may experience this impact to differing extents due to postural stability differences. Therefore, the authors investigated the effect of load magnitude on dynamic postural stability in men and women during a landing and stabilization task. Dynamic postural stability of 32 subjects (16 women) was assessed during the unilateral landing of submaximal jumps under 3 load conditions: +0%, +20%, and +30% body weight. Dynamic postural stability was measured using the dynamic postural stability index, which is calculated from ground reaction force data sampled at 1200 Hz. Two-way mixed-measures analysis of variance compared dynamic postural stability index scores between sexes and loads. Dynamic postural stability index scores were significantly affected by load (P = .001) but not by sex or by the sex by load interaction (P > .05). Dynamic postural stability index scores increased between the 0% (0.359 ± 0.041), 20% (0.396 ± 0.034), and 30% (0.420 ± 0.028) body weight conditions. Increased load negatively affects dynamic postural stability with similar performance decrements displayed by men and women. Men and women warfighters may experience similar performance decrements under load carriage conditions of similar relative magnitudes.

Reliability and Validity of a Pool-Based Maximal Oxygen Uptake Test to Examine High-Intensity Short-Duration Freestyle Swimming Performance.

Nagle, EF, Nagai, T, Beethe, AZ, Lovalekar, MT, Zera, JN, Connaboy, C, Abt, JP, Beals, K, Nindl, BC, Robertson, RJ, and Lephart, SM. Reliability and validity of a pool-based maximal oxygen uptake test to examine high-intensity short-duration freestyle swimming performance. J Strength Cond Res 33(5): 1208-1215, 2019-A modality-specific swimming protocol to assess maximal oxygen uptake (V[Combining Dot Above]O2maxsw) is essential to accurately prescribe and monitor swimming conditioning programs. Consequently, there is a need for a reliable and valid graded intensity swimming pool test to accurately assess V[Combining Dot Above]O2maxsw using indirect calorimetry. The purpose of this study was to assess (a) reliability of an intensity self-regulated swimming pool test of V[Combining Dot Above]O2maxsw and (b) validity of a V[Combining Dot Above]O2maxsw test using performance swim (PS) time as the criterion. Twenty-nine men (n = 15) and women (n = 14) (age, 23 ± 6.4 years; body mass index, 23.5 ± 3.0 kg·m) performed 2 swimming pool V[Combining Dot Above]O2maxsw trials (V[Combining Dot Above]O2maxsw A and V[Combining Dot Above]O2maxsw B), and 2 PS tests (45.7 m [31.20 ± 4.5 seconds] and 182 m [159.2 ± 25.5 seconds]). For test-retest reliability (trials A vs. B), strong correlations (p < 0.05) were found for V[Combining Dot Above]O2maxsw (ml·kg·min) (r = 0.899), O2 pulse (ml O2·beat) (r = 0.833), and maximum expired ventilatory volume (L·min) (r = 0.785). For performance validity, moderately strong correlations (p < 0.05) were found between V[Combining Dot Above]O2maxsw A and 45.7-m (r = -0.543) and 182-m (r = -0.486) swim times. The self-regulated graded intensity swimming pool protocol examined presently is a reliable and valid test of V[Combining Dot Above]O2maxsw. Studies should consider the suitability of a V[Combining Dot Above]O2maxsw test for military personnel, clinical populations, and injured athletes.

The Relationship of Core Strength and Activation and Performance on Three Functional Movement Screens.

Johnson, CD, Whitehead, PN, Pletcher, ER, Faherty, MS, Lovalekar, MT, Eagle, SR, and Keenan, KA. The relationship of core strength and activation and performance on three functional movement screens. J Strength Cond Res 32(4): 1166-1173, 2018-Current measures of core stability used by clinicians and researchers suffer from several shortcomings. Three functional movement screens appear, at face-value, to be dependent on the ability to activate and control core musculature. These 3 screens may present a viable alternative to current measures of core stability. Thirty-nine subjects completed a deep squat, trunk stability push-up, and rotary stability screen. Scores on the 3 screens were summed to calculate a composite score (COMP). During the screens, muscle activity was collected to determine the length of time that the bilateral erector spinae, rectus abdominis, external oblique, and gluteus medius muscles were active. Strength was assessed for core muscles (trunk flexion and extension, trunk rotation, and hip abduction and adduction) and accessory muscles (knee flexion and extension and pectoralis major). Two ordinal logistic regression equations were calculated with COMP as the outcome variable, and: (a) core strength and accessory strength, (b) only core strength. The first model was significant in predicting COMP (p = 0.004) (Pearson's Chi-Square = 149.132, p = 0.435; Nagelkerke's R-Squared = 0.369). The second model was significant in predicting COMP (p = 0.001) (Pearson's Chi-Square = 148.837, p = 0.488; Nagelkerke's R-Squared = 0.362). The core muscles were found to be active for most screens, with percentages of "time active" for each muscle ranging from 54-86%. In conclusion, performance on the 3 screens is predicted by core strength, even when accounting for "accessory" strength variables. Furthermore, it seems the screens elicit wide-ranging activation of core muscles. Although more investigation is needed, these screens, collectively, seem to be a good assessment of core strength.

Gender Differences in Static and Dynamic Postural Stability of Soldiers in the Army's 101st Airborne Division (Air Assault).

CONTEXT: Postural stability is essential for injury prevention and performance. Differences between genders may affect training focus. OBJECTIVE: To examine static and dynamic postural stability in male and female soldiers. DESIGN: Descriptive laboratory study. SETTING: Biomechanics laboratory. PARTICIPANTS: 25 healthy female soldiers (26.4 ± 5.3 y) and 25 healthy male soldiers (26.4 ± 4.9 y) matched on physical demand rating and years of service from the Army's 101st Airborne Division (Air Assault). INTERVENTIONS: Each person underwent static and dynamic postural stability testing. MAIN OUTCOME MEASURES: Standard deviation of the ground reaction forces during static postural stability and the dynamic stability index for dynamic postural stability. RESULTS: Female soldiers had significantly better static postural stability than males but no differences were observed in dynamic postural stability. CONCLUSIONS: Postural stability is important for injury prevention, performance optimization, and tactical training. The differences observed in the current study may indicate the need for gender-specific training emphasis on postural stability.

Energy Drinks Improve Five-Kilometer Running Performance in Recreational Endurance Runners.

Prins, PJ, Goss, FL, Nagle, EF, Beals, K, Robertson, RJ, Lovalekar, MT, and Welton, GL. Energy drinks improve five-kilometer running performance in recreational endurance runners. J Strength Cond Res 30(11): 2979-2990, 2016-The purpose of this study was to evaluate exercise performance time and related physiological and perceptual responses of recreational endurance runners after they had ingested a commercially available energy drink (Red Bull, Red Bull GmbH, Fuschl am See, Austria) containing caffeine, glucose, and taurine. Recreational endurance runners (n = 18; 13 men and 5 women; age: 20.39 ± 3.27 years; weight: 71.25 ± 17.17 kg; height: 178.00 ± 7.57 cm; V[Combining Dot Above]O2max: 55.94 ± 7.66 ml·kg·min) participated in a double-blind, crossover, repeated-measures study where they were randomized to supplement with 500 ml of the commercially available energy drink Red Bull and a noncaffeinated, sugar-free placebo (PLA) 60 minutes before completing a 5-km time trial on a treadmill, separated by 7 days. Heart rate, rating of perceived exertion (RPE) (RPE-Overall; RPE-Chest; RPE-Legs), and affect were recorded at rest, 1 hour before ingestion, at 5-minute intervals during the 5-km time trial, and immediately after exercise. Session RPE and session affect were obtained 5 minutes after completion of the 5-km time trial. The distance covered at each 5-minute interval during the 5-km time trial was recorded. Performance improved with the energy drink compared with placebo (Red Bull: 1,413.2 ± 169.7 vs. PLA: 1,443.6 ± 179.2 seconds; p = 0.016), but there were no differences in RPE, affect, session RPE, session affect, or the distance covered at 5-minute splits between the two 5-km time trials (p > 0.05). These results demonstrate that consuming a commercially available energy drink before exercise can improve 5-km performance. These results may have application for altering pre-exercise nutritional strategies in recreational runners.

Block-Periodized Training Improves Physiological and Tactically Relevant Performance in Naval Special Warfare Operators.

Human performance training and prevention strategies are necessary to promote physical readiness and mitigate musculoskeletal injuries of the Naval Special Warfare (NSW) Operator. The purpose of this study was to measure the effectiveness of 2 training programs when performed during a training evolution of Operators. A total of 85 Operators (experimental: n = 46, age: 29.4 ± 5.5 years, height: 176.7 ± 6.4 cm, mass: 86.7 ± 11.6 kg; control: n = 39, age: 29.0 ± 6.0 years, height: 177.1 ± 6.3 cm, mass: 85.7 ± 12.5 kg) participated in a trial to measure the effectiveness of these programs to improve physical, physiological, and performance characteristics. Operators in the experimental group performed a 12-week block-periodized program, whereas those in the control group performed a nonlinear periodized program. Pretesting/posttesting was performed to assess body composition, aerobic capacity/lactate threshold, muscular strength, flexibility, landing biomechanics, postural stability, and tactically relevant performance. The experimental group demonstrated a significant loss in body fat, fat mass, and body mass compared with the control group, whereas aerobic capacity increased for the both groups. The experimental group demonstrated a significant increase in posterior shoulder flexibility and ankle dorsiflexion, whereas the control group had a significant reduction in shoulder, knee, and ankle flexibility. The experimental group also improved landing strategies and balance. Both groups improved upper and lower muscular power and upper-body muscular endurance, whereas only the experimental group demonstrated significant improvements in agility and total body muscular strength. Implementation of a population-specific training program provides structured and progressive training effectively and promotes physical readiness concurrently with tactical training without overload.

The effects of fatiguing exercise and load carriage on the perception and initiation of movement.

Perceptual-motor coordination relies on the accurate coupling of the perceptual and movement systems. However, individuals must also be able to recalibrate to perturbations to perceptual and movement capabilities. We examined the effects of fatigue and load carriage on perceptual-motor coordination for a maximal leaping task. 23 participants completed an incremental fatigue protocol (light to fatiguing intensity stages) on two separate occasions (loaded/unloaded). At baseline and the end of every stage of the protocol, participants made perceptual judgments for the affordance of leaping. The accuracy of responses and reaction times were calculated and mean differences were assessed across exercise intensity and load carriage conditions. No interaction of exercise intensity and load carriage was detected, or main effect of load carriage. A main, quadratic effect of exercise intensity was detected on reaction times, with times decreasing through the moderate stage and increasing through post-fatigue. No effect of exercise/fatigue was detected on perceptual accuracy. The results indicate that exercise at high intensities through fatigue has a significant effect on perceptual-motor calibration. Contrastingly, in response to an action-scaled task, individuals can adequately recalibrate to increased load carriage.

The key to life nutrition program: results from a community-based dietary sodium reduction trial.

OBJECTIVE: Evaluation of a dietary Na reduction trial in a community setting. DESIGN: Community-based randomized trial. Ten-week nutrition intervention activities focused on lifestyle modification to decrease dietary Na intake, under the supervision of a registered dietitian. Twenty-four hour urine specimens were collected at baseline and follow-up visits to determine 24 h urinary Na excretion. SETTING: The University of Pittsburgh Center for Healthy Aging, Key to Life Nutrition Program. SUBJECTS: Hypertensive adults at least 65 years of age. RESULTS: Mean age of participants was 75 years. Twenty-four hour mean urinary Na excretion at baseline was 3174 mg/d. This reduced to 2944 mg/d (P = 0.30) and 2875 mg/d (P or=1000 ml, baseline to 12 months), mean urinary Na excretion decreased from 3220 mg/d to 2875 mg/d (P

Evaluation of Shoulder Strength and Kinematics as Risk Factors for Shoulder Injury in United States Special Forces Personnel.

BACKGROUND: Musculoskeletal injuries at the shoulder are highly prevalent and place a large burden on United States Special Forces personnel. Literature is lacking regarding the risk factors for these types of injuries. PURPOSE/HYPOTHESIS: The purpose of this study was to evaluate the association of shoulder strength and kinematic characteristics, which have shown retrospective associations with shoulder conditions/injuries, with prospectively collected shoulder injuries. We hypothesized that lower strength and abnormal kinematics would be predictive of future shoulder injury. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: A total of 140 male Special Forces operators underwent a musculoskeletal evaluation of the shoulder that included a scapular kinematic assessment during a humeral elevation task and isokinetic strength testing of the scapular protractors/retractors, external/internal rotators, and elevators of the shoulder. From strength assessments, ipsilateral strength ratios and bilateral strength asymmetries were also calculated. Musculoskeletal injuries of the shoulder were collected prospectively by use of medical chart reviews at 365 days following the evaluation. Separate generalized estimating equations (GEEs) and simple logistic regressions were used to analyze the association between baseline predictors and development of shoulder injury. RESULTS: Results of the GEEs showed no significant prediction of shoulder injury by shoulder strength (odds ratio [OR], 1.00-1.03), ipsilateral strength ratios (OR, 0.43-2.12), or scapular kinematics (OR, 0.99-1.01). Logistic regression indicated that none of the bilateral asymmetries were significantly predictive of shoulder injury (OR, 1.00-1.04). CONCLUSION: The results indicate that shoulder strength and kinematic characteristics are not risk factors for shoulder injury in the Special Forces population. These findings are in opposition to the general findings of previous research using a retrospective analysis.

Prediction of exertional lower extremity musculoskeletal injury in tactical populations: protocol for a systematic review and planned meta-analysis of prospective studies from 1955 to 2018.

BACKGROUND: Musculoskeletal injuries (MSI) represent more than half of all injuries in tactical populations (i.e., military service and public safety workers including police, firefighters, emergency medical services (EMS)). Most lower extremity MSIs result from physical exertion during training, occupational tasks, and recreation. Such exertional lower extremity injuries (ELEI) produce a significant human and financial cost. Accordingly, significant efforts have been made to identify sensitive, specific, and reliable predictors of ELEI. There is a need to synthesize and evaluate the predictive value of risk factors for ELEI while addressing the influence of occupation, sex, exposure, injury characteristics, and study quality. Therefore, the purpose of this systematic review and planned meta-analysis is to evaluate risk factors for ELEI in tactical populations. METHODS: After the development of a search strategy, comprehensive searches will be conducted in MEDLINE, EMBASE, Cochrane, and CINAHL databases. Articles will be screened with a multi-user process and delimited to prospective comparative cohort studies that directly measure injury occurrence in the target population(s). Extracted data will be synthesized and assessed for reporting bias, meta-bias, and overall quality, with subgroup analyses to determine the influence of participant, injury, and exposure characteristics in addition to study quality. DISCUSSION: This systematic review and planned meta-analysis will comprehensively evaluate ELEI risk factors. Information gained will inform injury prevention protocols, facilitate the use of improved measurements, and identify requirements for future research. TRIAL REGISTRATION: The systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 3 Jan 2018 (registration number CRD42018056977 ).

Military personnel with self-reported ankle injuries do not demonstrate deficits in dynamic postural stability or landing kinematics.

BACKGROUND: The odds of sustaining non-contact musculoskeletal injuries are higher in Special Operations Forces operators than in infantry soldiers. The ankle is one of the most commonly injured joints, and once injured can put individuals at risk for reinjury. The purpose of this study was to determine if any differences in postural stability and landing kinematics exist between operators with a self-reported ankle injury in the past one year and uninjured controls. METHODS: A total of 55 Special Operations Forces operators were included in this analysis. Comparisons were made between operators with a self-reported ankle injury within one-year of their test date (n=11) and healthy matched controls (n=44). Comparisons were also made between injured and uninjured limbs within the injured group. Dynamic postural stability and landing kinematics at the ankle, knee, and hip were assessed during a single-leg jump-landing task. Comparisons were made between groups with independent t-tests and within the injured group between limbs using paired t-tests. FINDINGS: There were no significant differences in dynamic postural stability index or landing kinematics between the injured and uninjured groups. Anterior-posterior stability index was significantly higher on the uninjured limb compared to the injured limb within the injured group (P=0.02). INTERPRETATION: Single ankle injuries sustained by operators may not lead to deficits in dynamic postural stability. Dynamic postural stability index and landing kinematics within one year after injury were either not affected by the injuries reported, or injured operators were trained back to baseline measures through rehabilitation and daily activity.

Descriptive Epidemiology of Musculoskeletal Injuries in the Army 101st Airborne (Air Assault) Division.

The purpose of this study was to describe the epidemiology of musculoskeletal injuries among Soldiers of the 101st Airborne (Air Assault) Division. A total of 451 subjects (age: 27.6 ± 6.2 years, gender: males 395/451 = 87.6%) volunteered. Musculoskeletal injury data were extracted from subjects' medical charts and injuries that occurred during 1 year were described. Injury frequency, injury anatomic location and sublocation, injury cause, activity when injury occurred, and injury type were described. Injury frequency was 29.5 injuries per 100 subjects per year. Most injures affected the lower extremity (60.2% of injuries) and common anatomic sublocations for injuries were the ankle (17.3%) and knee (15.0%). Frequent causes of injuries were running (13.5%) and direct trauma (9.0%). Physical training was associated with 29.3% of the injuries. A majority of injuries were classified as pain/spasm/ache (29.3%), without further elucidation of pathology. Other frequent injury types were sprain (21.8%) and strain (14.3%). The descriptive epidemiology of musculoskeletal injuries in this population underscores the need to explore the modifiable risk factors of potentially preventable lower extremity injuries associated with physical training and running. There is scope for the development of an optimized and targeted physical training program for injury prevention in this population.

Injury epidemiology of U.S. Army Special Operations forces.

Musculoskeletal injuries have long been a problem in general purpose forces, yet anecdotal evidence provided by medical, human performance, and training leadership suggests musculoskeletal injuries are also a readiness impediment to Special Operations Forces (SOF). The purpose of this study was to describe the injury epidemiology of SOF utilizing self-reported injury histories. Data were collected on 106 SOF (age: 31.7 ± 5.3 years, height: 179.0 ± 5.5 cm, mass: 85.9 ± 10.9 kg) for 1 year before the date of laboratory testing and filtered for total injuries and those with the potential to be preventable based on injury type, activity, and mechanism. The frequency of musculoskeletal injuries was 24.5 injuries per 100 subjects per year for total injuries and 18.9 injuries per 100 subjects per year for preventable injuries. The incidence of musculoskeletal injuries was 20.8 injured subjects per 100 subjects per year for total injuries and 16.0 injured subjects per 100 subjects per year for preventable injuries. Preventable musculoskeletal injuries comprised 76.9% of total injuries. Physical training (PT) was the most reported activity for total/preventable injuries (PT Command Organized: 46.2%/60.0%, PT Noncommand Organized: 7.7%/10.0%, PT Unknown: 3.8%/5.0%). Musculoskeletal injuries impede optimal physical readiness/tactical training in the SOF community. The data suggest a significant proportion of injuries are classified as preventable and may be mitigated with human performance programs.