The impact of inter-limb leg lean tissue mass asymmetry on stair climb performance in career firefighters.

The purpose of this study was to examine the influence of inter-limb leg lean tissue mass (LTM) asymmetry on stair climb (SC) performance in firefighters. Forty-one career firefighters (age = 32.3 ± 8.2 years, body mass = 92.1 ± 18.6 kg, stature = 178.3 ± 7.9 cm) visited the laboratory on one occasion and completed a whole body and leg composition assessment followed by a timed and weighted SC task. Percent body fat (%BF) and leg LTM were determined during a DEXA scan and regional thigh analysis. Asymmetry was assessed by the percent difference between limbs (dominant limb LTM - non-dominant limb LTM)/dominant limb LTM × 100) and a ± 3% cut-off for asymmetry classification. Participants ascended and descended 26 stairs four times as quickly as possible while wearing a weighted (22 kg) vest. Point biserial correlations were used to assess the relationship of inter-limb leg LTM asymmetry and SC performance before and after controlling for age and %BF. Results indicated that inter-limb leg LTM asymmetry was associated with longer SC task time (poorer performance) both before (r = 0.432, P = 0.005) and after (r = 0.502, P = 0.001) controlling for age and %BF. Our findings indicated that inter-limb leg LTM asymmetry negatively impacts firefighter SC performance, which may be improved with appropriate exercise interventions.

This study examined the influence of leg inter-limb lean tissue mass (LTM) asymmetry on SC performance in career firefighters. We found that inter-limb leg LTM asymmetry was associated with reduced SC performance, prior to and after controlling for age and percent body fat. Interventions that mitigate these asymmetries may improve occupational performance.

Impact of Age on the Affective Responses Following Worksite Resistance Exercise in Career Firefighters.

INTRODUCTION: The purpose of this study was to examine the impact of age on the affective responses (attitude, feelings, self-efficacy, intention, enjoyment, and fondness) after a worksite circuit-style resistance exercise routine in career firefighters. METHODS: Nineteen young (25.5 ± 3.3 yr) and 19 middle-aged male career firefighters (50.3 ± 3.5 yr) completed 2 d of physical testing at local fire stations. Participants were familiarized with the resistance training exercises (deadlift, shoulder press, lunge, and upright row) at visit 1 and performed a multirepetition maximum (RM) assessment to prescribe the appropriate loads for the resistance exercise bout on visit 2. The resistance training session included three sets of 8 to 10 repetitions per exercise at 80% 1-RM. Participants completed a postexercise questionnaire examining affective responses and a rating of perceived exertion (RPE). Mann-Whitney U tests and an independent t-test were used to determine differences between the young and middle-aged firefighters' affective responses and RPE, respectively. RESULTS: There were no significant differences between groups for any of the six affective responses ( P = 0.062-0.819) or RPE ( P = 0.142). CONCLUSIONS: Age did not influence the perceived effort or affective responses following an acute bout of worksite resistance exercise. Firefighters reported overall positive attitudes, feelings, and fondness paired with high self-efficacy and intention at a training frequency of twice per week. However, confidence, intention, and enjoyment decreased at higher training frequencies (i.e., 3-4x per week). Circuit-style resistance training performed twice per week may be a feasible and practical worksite exercise routine across ages in the fire service.

Neuromuscular determinants of simulated occupational performance in career firefighters.

PURPOSE: Although firefighters are required to perform various high-intensity critically essential tasks, the influence of neuromuscular function on firefighter occupational performance is unclear. The primary aim of the current study was to identify the key neuromuscular determinants of stair climb (SC) performance in firefighters. METHODS: Leg extension isometric peak torque (PT), peak power (PP), torque steadiness at 10% (Steadiness10%) and 50% (Steadiness50%) of PT, fatigability following 30 repeated isotonic concentric contractions at 40% of PT, percent body fat (%BF), and a weighted and timed SC task were examined in 41 (age: 32.3 ± 8.2 yrs; %BF: 24.1 ± 7.9%) male career firefighters. RESULTS: Faster SC times (74.7 ± 13.4 s) were associated with greater PT and PP, less fatigability, younger age, and lower %BF (r = -0.530-0.629; P ≤ 0.014), but not Steadiness10% or Steadiness50% (P ≥ 0.193). Stepwise regression analyses indicated that PP and Steadiness50% were the strongest predictors of SC time (R2 = 0.442, P < 0.001). However, when age and %BF were included in the model, these variables became the only significant predictors of SC time (R2 = 0.521, P < 0.001) due to age and %BF being collectively associated with all the neuromuscular variables (excluding Steadiness10%). CONCLUSIONS: Lower extremity neuromuscular function, specifically PP and steadiness, and %BF are important modifiable predictors of firefighter SC performance, which becomes increasingly important in aging firefighters.

The influence of age on the recovery from worksite resistance exercise in career firefighters.

Resistance exercise is an important strategy to reduce injuries and improve performance in the fire service. However, given the large age range of firefighters, it is important to determine if age influences their recovery following an acute bout of resistance exercise. PURPOSE: To examine the changes in indirect markers of muscle damage in young and older firefighters following a feasible worksite resistance exercise routine. METHODS: Nineteen young (25.5 ± 3.4 years) and 19 older male career firefighters (50.3 ± 3.5 years) completed pre-testing, an acute bout of resistance exercise, and post-testing at 24, 48, and 72 h post-exercise at their fire station. Prior to all testing, firefighters completed a work-related fatigue (WRF) questionnaire to account for potential unanticipated differences in previous shift workloads. Testing included perceived muscle soreness, ultrasonography to quantify muscle size and echo intensity (EI) of the vastus lateralis (VL) and biceps brachii (BB), countermovement jump (CMJ) height and velocity, upper body (UB) peak force (PF), lower body (LB) PF and rapid force, and electromyographic (EMG) amplitude of the VL. The resistance training session included 3 sets of 8-10 repetitions of a deadlift, shoulder press, lunge, and upright row exercise at 80% 1-RM. All recovery variables were analyzed using a linear mixed model, controlling for WRF. RESULTS: There was no interaction (age × time) for any of the variables and a similar training volume were completed between groups (P ≥ 0.171). Muscle soreness, CMJ height and velocity, UB PF, LB rapid force and EMG amplitude at later time intervals (100-200 ms), and VL and BB muscle size were altered from baseline (P ≤ 0.044) for 48, 24, 48, 72, and 72 h post-exercise, respectively. Young firefighters exhibited greater CMJ height and velocity, LB PF, LB rapid force (200 ms), and lower VL EI values than the older firefighters (P ≤ 0.047). CONCLUSIONS: Age did not influence the recovery from an acute bout of worksite resistance exercise in firefighters. However, UB muscle strength, CMJ performance, and LB rapid force production were reduced 24-72 h post-exercise. Appropriately scheduled and chronic on-duty resistance training may mitigate these decrements.

Measuring muscle quality: associations between echo intensity and normalized strength and power.

Objective. Muscle quality has received considerable attention within the literature due to its influence on health and performance. However, it has been assessed by various measures (e.g. ultrasound imaging, normalized strength), contributing to a lack of a consensus definition. The purpose of this study was to investigate the association between common muscle quality measures: vastus lateralis echo intensity (EI) and peak torque (PT) and power (PP) normalized to thigh lean mass (TLM) and thigh fat mass (TFM).Approach. Participants' (n = 39; age = 32.7 ± 8.2 years; %BF = 24.1% ±8.1%) whole body and leg composition was assessed via dual-energy x-ray absorptiometry and custom thigh analyses. Subcutaneous fat-corrected muscle EI was assessed via ultrasonography. Maximal PT and PP of the dominant leg extensors were examined on a calibrated dynamometer and were normalized to both TLM and TFM, respectively. Pearson product-moment correlations were used to examine the associations between EI and PT/TLM, PT/TFM, PP/TLM, and PP/TFM.Main results. Greater muscle EI was significantly related with lower PT/TFM and PP/TFM (r = -0.74 to -0.70,P < 0.001), but unrelated to PT/TLM or PP/TLM (P ≥ 0.205).Significance. These findings suggest that ultrasound imaging (muscle EI) and normalized strength and power may not be used interchangeably to define muscle quality, and muscle EI may be more sensitive to the adiposity of the limb than TLM. Future research should consider using separate and consistent definitions when referring to imaging-derived or normalized strength and power values of muscle quality.