Bradley C. Nindl

Maximum Acceptable Load for Lifting and Carrying in Two-Person Teams

The purpose of this study was to determine and verify the maximum acceptable load for lifting and carrying (MALL&C) in single- and mixed-gender two-person teams. Participants lifted and carried a box 7.2 meters and placed it on a 132 cm high shelf, at rates of 1 x/min and 4 x/min. All male teams lifted and carried significantly (p<.05) more weight than all female teams or mixed-gender teams, and mixed-gender teams carried more than all female teams (p>.05). Our findings demonstrate that 1) individuals working alone or in teams can accurately estimate their ability to lift and carry loads for an hour, and that 2) when working in pairs, team MAL-L&C are approximately equal to the sum of their individual MAL-L&C. Percentile norms for MAL-L&Cs are provided for male, female, and mixed gender teams.

Prediction of Two-Person Team Lifting Capacity

Predictive models for team lifting capacity are important for task and equipment design, as well as worker selection and placement. The purpose of this study was to develop a prediction equation for single gender and mixed gender two-person team lifting from the floor to knuckle height. Men (n=23) and women (n=17) were combined into teams of two men (n=26), two women (n=24), and one man with one woman (n=25). Independent variables included incremental dynamic lift, 38 cm upright pull, dead lift, fat free mass, and body mass. A least squares linear regression was used. In addition, an equation was developed from deadlift strengths only. The lightest individual deadlift and the sum of the individual deadlifts were the best predictors of team lifting capacity (R2 = 0.90, SEE = 16). The results indicate that two-person team lifts to knuckle height are determined by the weaker team member.

Highlighted Topics: Recovery from Exercise: Recovery Responses of Testosterone, Growth Hormone, and IGF-1 after Resistance Exercise

The complexity and redundancy of the endocrine pathways during recovery related to anabolic function in the body belie an oversimplistic approach to its study. The purpose of this review is to examine the role of resistance exercise (RE) on the recovery responses of three major anabolic hormones, testosterone, growth hormone(s), and insulin-like growth factor 1. Each hormone has a complexity related to differential pathways of action as well as interactions with binding proteins and receptor interactions. Testosterone is the primary anabolic hormone, and its concentration changes during the recovery period depending on the upregulation or downregulation of the androgen receptor. Multiple tissues beyond skeletal muscle are targeted under hormonal control and play critical roles in metabolism and physiological function. Growth hormone (GH) demonstrates differential increases in recovery with RE based on the type of GH being assayed and workout being used. IGF-1 shows variable increases in recovery with RE and is intimately linked to a host of binding proteins that are essential to its integrative actions and mediating targeting effects. The RE stress is related to recruitment of muscle tissue with the glandular release of hormones as signals to target tissues to support homeostatic mechanisms for metabolism and tissue repair during the recovery process. Anabolic hormones play a crucial role in the bodys response to metabolism, repair, and adaptive capabilities especially in response to anabolic-type RE. Changes of these hormones following RE during recovery in the circulatory biocompartment of blood are reflective of the many mechanisms of action that are in play in the repair and recovery process.

Human skeletal muscle type 1 fibre distribution and response of stress-sensing proteins along the titin molecule after submaximal exhaustive exercise

Early responses of stress-sensing proteins, muscle LIM protein (MLP), ankyrin repeat proteins (Ankrd1/CARP and Ankrd2/Arpp) and muscle-specific RING finger proteins (MuRF1 and MuRF2), along the titin molecule were investigated in the present experiment after submaximal exhaustive exercise. Ten healthy men performed continuous drop jumping unilaterally on a sledge apparatus with a submaximal height until complete exhaustion. Five stress-sensing proteins were analysed by mRNA measurements from biopsies obtained immediately and 3xa0h after the exercise from exercised vastus lateralis muscle while control biopsies were obtained from non-exercised legs before the exercise. Decreased maximal jump height and increased serum creatine kinase activities as indirect markers for muscle damage and HSP27 immunostainings on muscle biopsies as a direct marker for muscle damage indicated that the current exercised protocol caused muscle damage. mRNA levels for four (MLP, Ankrd1/CARP, MuRF1 and MuRF2) out of the five studied stress sensors significantly (pxa0<xa00.05) increased 3xa0h after fatiguing exercise. The magnitude of MLP and Ankrd2 responses was related to the proportion of type 1 myofibres. Our data showed that the submaximal exhaustive exercise with subject’s own physical fitness level activates titin-based stretch-sensing proteins. These results suggest that both degenerative and regenerative pathways are activated in very early phase after the exercise or probably already during the exercise. Activation of these proteins represents an initial step forward adaptive remodelling of the exercised muscle and may also be involved in the initiation of myofibre repair.

Hormonal response patterns are differentially influenced by physical conditioning programs during basic military training

OBJECTIVESnCompare traditional military physical training and more contemporary physical training on catabolic and anabolic hormones and body composition in recruits undertaking basic military training (BMT).nnnDESIGNnA prospective cross-sectional study design.nnnMETHODSnTwo recruit intakes were assessed over the 12-week Australian Army BMT course. The control group (CON) comprised 40 recruits (26M/14F) and the experimental group (EXP) comprised 35 recruits (25M/10F). Hormone concentrations (IGF-I, testosterone, cortisol, SHBG) and body composition were assessed at weeks 1 and 12. The EXP group undertook a higher-load/intensity physical training regimen, while CON undertook the extant physical training program which focused on cardiovascular and muscular endurance. Total physical activity within physical training sessions was assessed during weeks 2, 6 and 9.nnnRESULTSnThere was a significant group×time interaction (p<0.01) for IGF-I and cortisol, and main effects over time (p<0.01) for IGF-I, cortisol and SHBG. There were main effects for time (p<0.05) for lean and fat mass, and these changes were associated (p<0.05) with altered hormone concentrations. Physical activity levels were approximately 50% lower in EXP than CON during physical training sessions.nnnCONCLUSIONSnThis is the first study to report a differential hormone response to contrasting physical conditioning regimen during BMT. The results indicate that the recruits who completed the EXP physical training regimen had an attenuated stress profile. This is an important observation, as any enhancement of recruit training outcomes are critical for Army noting that fundamentally, organisational capability is reliant upon the physical capability of its personnel.

Active and passive recovery influence responses of luteinizing hormone and testosterone to a fatiguing strength loading

The purpose of this study was to examine the acute hormonal and muscular responses to a strenuous strength loading [bilateral leg press (LP) 10u2009×u200910 1RM] followed by loading-specific active (AR, nu2009=u20097, LP 10u2009×u200910u2009×u200930% 1RM) or passive (PR, nu2009=u200911, seated) recovery. The subjects were men age: 26u2009±u20094 years, height: 174u2009±u20098xa0cm, body mass: 75u2009±u200913xa0kg. After control measurements, experimental measurements were conducted at pre- and post-loading as well as post-recovery and next morning. A significantly higher absolute concentration (pu2009<u20090.05) of serum luteinizing hormone (LH) was observed in AR than PR at next morning while no differences were observed in serum testosterone (T), cortisol (C) or sex hormone binding globulin (SHBG). Significant differences in relative hormonal responses to the loading were observed at next morning with greater responses observed in AR than in PR in terms of LH, and T (pu2009<u20090.05). Maximal bilateral isometric force (MVC) and countermovement jump height (CMJ) decreased significantly (pu2009<u20090.001) from the control measurements in both AR and PR but returned to control levels by next morning. No between-group differences were observed in mean absolute or relative changes in MVC or CMJ. From a hormonal perspective, the present AR method appears to have had some favorable effects following the strenuous strength loading; however, acute decreases in muscular force production did not significantly differ between groups. These results provide insight into the development of training programs that may help to support the performance of individuals involved in strenuous tasks.

Functional physical training improves women’s military occupational performance

The U.S. Armed Forces have recently approved full integration of women into combat roles. Physical fitness demands for executing Military Occupational Specialties (MOS) are substantial; thus lifting and load carriage capability improvements are desirable.nnnOBJECTIVESnTo determine if a specially-designed physical conditioning program could lessen the gap between the performance of male and female Soldiers in lifting and load carriage and thereby enable women to meet the requirements of most, if not all, Army MOSs.nnnMETHODSnForty women participated in a 24-week physical training program, which included resistance training, long-distance running, backpacking, and specialized drills. Pre- and post-tests of occupational and physical performance measures were conducted before and after training. Repeated measures analysis of variance were used to determine statistically significant differences among the pre-, mid- and posttests.nnnRESULTSnWomen increased maximal occupational lifting strength 12-20 kg, added 9-34 repetitions in lifting endurance, increased 0.23 m in jumping performance, added 46 repetitions in local muscular endurance, and decreased load carriage for time by 3.7-8.6 min. Women scored within 82-94% of untrained male scores for aerobic capacity and muscular endurance after training.nnnCONCLUSIONnWomens ability to perform physically-demanding military occupational tasks was significantly improved following 6 months of concurrent training, with emphasis on load carriage and lifting. The percentage of women that qualified for current heavy and very heavy MOSs was initially 24%, but increased to 78% after training. A resistance training program of 6+ months can adequately prepare women for heavy to very heavy MOSs.

Differential basal and exercise-induced IGF-I system responses to resistance vs. calisthenic-based military readiness training programs

OBJECTIVEnThe purpose of this study was to: 1) evaluate differential responses of the IGF-I system to either a calisthenic- or resistance exercise-based program and 2) determine if this chronic training altered the IGF-I system during an acute resistance exercise protocol.nnnDESIGNnThirty-two volunteers were randomly assigned into a resistance exercise-based training (RT) group (n=15, 27±5y, 174±6cm, 81±12kg) or a calisthenic-based training group (CT) (n=17, 29±5y, 179±8cm, 85±10kg) and all underwent 8weeks of exercise training (1.5h/d, 5d/wk). Basal blood was sampled pre- (Week 0), mid- (Week 4) and post-training (Week 8) and assayed for IGF-I system analytes. An acute resistance exercise protocol (AREP) was conducted preand post-training consisting of 6 sets of 10 repetitions in the squat with two minutes of rest in between sets and the IGF-I system analytes measured. A repeated measures ANOVA (p≤0.05) was used for statistical analysis.nnnRESULTSnNo interaction or within-subject effects were observed for basal total IGF-I, free IGF-I, or IGFBP-1. IGFBP-2 (pre; 578.6±295.7post-training; 14.3±1.9μg/mL; p=0.01). An interaction was observed for the RT group as IGFBP-3 increased from pre to mid (3462.4±216.4 vs. 3962.2±227.9ng/mL), but was not significant at the post-training time point (3770.3±228.7ng/mL). AREP caused all analytes except free IGF-I (40% decrease) to increase (17-27%; p=0.001) during exercise, returning to baseline concentration into recovery.nnnCONCLUSIONnPost-training, bioavailable IGF-I recovered more rapidly post-exercise. 8wks of chronic physical training resulted in increased basal IGFBP-2 and IGFBP-3, decreased ALS, increased pre-AREP free IGF-I and a more rapid free IGF-I recovery post-AREP. While total IGF-I was insensitive to chronic physical training, changes were observed with circulating IGFBPs and bioavailable IGF-I. To glean the most robust information on the effects of exercise training, studies must move beyond relying solely on total IGF-I measures and should consider IGFBPs and bioavailable IGF-I as these components of the circulating IGF-I system are essential determinants of IGF-I physiological action.

Effects of Gender, Lift Height, Direction, and Load on the Ability to Estimate Weight

The study evaluated the effects of gender, lift height, direction (lift/lower), and load on the ability to correctly estimate weight handled. Seven women and six men lifted and lowered boxes to and from knuckle, waist, and shoulder heights. Subjects were asked to estimate weights corresponding to 50, 40, 30, and 20% of gender specific lifting strength to 152 cm. The difference between the actual and estimated weight (DIFF) was 100% greater for men than for women (F = 6.27, p = 0.03). When the percent difference was analyzed, there was no significant gender effect. The least accurate estimates occurred when lowering a weight from knuckle height (p < 0.05). The majority of subjects underestimated the weight and men underestimated more frequently than women (Chi2 = 12.57, p = 0.0004). Subjects overestimated the weight more often at higher weights. The results suggest that both men and women tend to underestimate weight, especially when lowering from knuckle height, possibly putting them at risk for injury.

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

BackgroundExertional lower body musculoskeletal injuries (ELBI) cost billions of dollars and compromise the readiness and job performance of military service and public safety workers (i.e., tactical populations). The prevalence and burden of such injuries underscores the importance of prevention efforts during activities necessary to sustain core occupational competencies. Attempts to synthesize prevention techniques specific to tactical populations have provided limited insight on the comparative efficacy of interventions that do not modify physical training practices. There is also a need to assess the influence of sex, exposure, injury classification scheme, and study design. Thus, the primary purpose of the systematic review and planned meta-analysis detailed in this protocol is to evaluate the comparative efficacy of ELBI prevention strategies in tactical populations.MethodsA systematic search strategy will be implemented in MEDLINE, EMBASE, Cochrane, and CINAHL. A multi-tiered process will be used to capture randomized controlled trials and prospective cohort studies that directly assess the prevention of ELBI in tactical population(s). Extracted data will be used to compare prevention strategies and assess the influence of heterogeneity related to occupation, sex, exposure, injury characteristics, and study quality. In addition, individual risk of bias, meta-bias, and the quality of the body of evidence will be rigorously tested.DiscussionThis systematic review and planned meta-analysis will comprehensively evaluate ELBI mitigation strategies in tactical populations, elucidate factors that influence responses to treatment, and assess the overall quality of the body of research. Results of this work will guide the prioritization of ELBI prevention strategies and direct future research efforts, with direct relevance to tactical, health and rehabilitation science, and human performance optimization stakeholders.Systematic review registrationThe systematic review protocol was registered with the International Prospective Register of Systematic Reviews (PROSPERO) on 3 Jan 2018 (registration number CRD42018081799).