The purpose of the current study was to determine the concurrent validity of the Elite HRV smartphone application when calculating heart rate variability (HRV) metrics in reference to an independent software criterion. A total of 5 minutes of R–R interval and natural log of root mean square of the successive differences (lnRMSSD) resting HRV data were simultaneously collected using two Polar H10 heart rate monitors (HRMs) in both the seated and supine positions from 22 participants (14 males, 8 females). One H10 HRM was paired with a Polar V800 watch and one with the Elite HRV application. When no artifact correction was applied, significant, but small, differences in the lnRMSSD data were observed between the software in the seated position (p = 0.022), and trivial and nonstatistically significant differences were observed in the supine position (p = 0.087). However, significant differences (p > 0.05) in the lnRMSSD data were no longer identifiable in either the seated or the supine positions when applying Very Low, Low, or Automatic artifact-correction filters. Additionally, excellent agreements (ICC_3,1 = 0.938 − 0.998) and very strong to near-perfect (r = 0.889 − 0.997) relationships were observed throughout all correction levels. The Elite HRV smartphone application is a valid tool for calculating resting lnRMSSD HRV metrics.

Approximately half of the injuries experienced by firefighters consist of musculoskeletal injuries (MSKIs). Functional movement quality may be associated with MSKI risk within this tactical athlete population. Previous research indicates that measures of body composition change among firefighter recruits progressing from academy training through active-duty service, but similar changes in functional movement quality have yet to be examined. The purpose of this study was to describe longitudinal changes in functional movement quality of firefighter recruits. Body mass index (BMI), body fat (BF), and Functional Movement Screen (FMS) data were collected from 26 male firefighter recruits at the onset (W1) and completion (W14) of their training academy, and at the completion of their probationary period of active-duty service (W38). After adjusting for changes in BMI and BF across time, significant changes (ps < 0.05) in Composite FMS scores were identified, with significant increases in from W1 to W14 and from W14 to W38, as well as an overall increase from W1 to W38. These results suggest that the development of firefighter-specific skills can decrease the MSKI risk of firefighter recruits by facilitating enhanced functional movement competencies, particularly during tasks that require single-leg movement and core strength and stability.

A new functional movement assessment, known as the Fusionetics- Movement Efficiency (ME) Test, has recently been introduced in the literature. Before the potential clinical utility of the ME Test can be examined, the reliability of this assessment must be established. To examine the intra-rater test-retest reliability of the Fusionetics- ME Test. Cross-sectional. ME Test data were collected among 23 (6 males, 17 females) university students (mean ± SD, age = 25.96 ± 3.16 yrs; height = 170.70 ± 9.96 cm; weight = 66.89 ± 12.67 kg) during sessions separated by 48 hours (Day 1, Day 2). All participants completed the seven sub-tests of the ME Test: 2-Leg Squat, 2-Leg Squat with Heel Lift, 1-Leg Squat, Push-Up, Shoulder Movements, Trunk Movements, and Cervical Movements. Overall ME Test scores and ME Test scores for each individual sub-test were calculated on a scale of 0 - 100 (worst - best) based on commonly observed movement compensations associated with each sub-test. Intraclass correlation coefficients (ICC3,1) statistics indicated that the intra-rater test-retest reliability of the Overall ME Test and individual sub-tests ranged from fair-to-excellent (ICC3,1 range = 0.55 - 0.84). Statistically significant differences in ME Test scores were identified between Day 1 and Day 2 among the 2-Leg Squat with Heel Lift (p = 0.015) and Cervical Movements (p = 0.005) sub-tests. In addition, a large range in the standard error of the measure (SEM) and minimal detectable change values (MDC90% & MDC95%) were identified within individual sub-tests of the ME Test (SEM range = 7.05 - 13.44; MDC90% range = 16.40 - 31.27; MDC95% range = 19.53 - 37.25), suggesting that the response stability varies among these individual sub-tests. Prevalence-adjusted bias-adjusted kappa statistics (κPABA) suggest that 55 of the 60 (92%) individual movement compensations hold moderate-to-almost perfect intra-rater test-retest reliability (κPABA range = 0.30 - 1.00). Excellent intra-rater test-retest reliability of the Overall ME Test score was identified, and thus, clinicians can reliably utilize the Fusionetics- ME Test to assess change in functional movement quality across time. However, caution should be taken if utilizing an individual sub-test to assess functional movement quality over time. 2b.

Firefighters have a sustained risk for experiencing a sudden cardiac event after completing a fire call. Heart rate recovery (HRR) can be utilized to characterize autonomic nervous system (ANS) recovery and has been linked to cardiac events. Research suggests that body composition influences post-exercise HRR responses in non-firefighter populations. The purpose of this study was to examine the influence of body mass index (BMI), waist circumference (WC), and percent body fat (BF) on the HRR response of firefighter recruits. BMI (kg·m⁻²), WC (cm), and BF (%) data from 57 firefighter recruits were collected. HRR (b·min⁻¹) data were collected at completion (HR₀), as well as 15 (HR₁₅), 30 (HR₃₀), 45 (HR₄₅), 60 (HR₆₀), 120 (HR₁₂₀), and 180 (HR₁₈₀) seconds following a submaximal step test, and commonly utilized clinical HRR indices were calculated (ΔHRR₃₀, ΔHRR₆₀, ΔHRR₁₂₀, and ΔHRR₁₈₀). After controlling for sex, linear mixed regression models did not identify significant interactions between body composition (ps > 0.05) and HRR response across time. However, significant (ps < 0.05) indirect semi-partial correlations were identified between BF and ΔHRR₃₀ (r_sp = −0.31) and ΔHRR₆₀ (r_sp = −0.27), respectively. Reducing overall BF (vs. BMI or WC) should be prioritized to improve the post-exercise ANS recovery of firefighter recruits.

In contrast to static stretching (SS), previous research has demonstrated increases in flexibility after an acute bout of self-myofascial release (SMR) without any subsequent decreases in force output. Previous research has utilized measures of surface electromyography (sEMG) and mechanomyography (MMG) to examine the influence of SS on the electrical and mechanical processes of muscle activation, respectively. However, there is a lack of research examining the potential changes in electro-mechanical muscle activation post-SMR. To examine the influence of SMR, via an acute bout of foam rolling (FR) to the vastus lateralis (VL), on the expression of knee extension force output and the inter-muscular electro-mechanical activation of the quadriceps musculature. Randomized crossover trial. Twenty (10 males, 10 females) recreationally-active participants with prior FR experience completed both SMR and control (CON) testing protocols during separate testing sessions that were conducted in a randomized order 48 hours apart. During the SMR protocol, participants performed 3 sets of 60 seconds of FR over the VL portion of their quadriceps musculature, with 60 seconds of rest between sets. During the CON protocol, participants quietly sat upright for 10 minutes. Peak knee extension force output ­(Forcepeak) data, as well as sEMG and MMG data from the VL and the rectus femoris (RF) were collected during maximal voluntary isometric contractions (MVICs) before and after both testing protocols. Root mean square sEMG and MMG amplitudes were calculated to represent electro-mechanical muscle activation of the VL (VL–sEMGRMS, VL–MMGRMS) and RF (RF–sEMGRMS, RF–MMGRMS) musculature. Repeated measures analyses of variance (RM ANOVAs) identified a significant (p < 0.05) increase in Forcepeak within the SMR protocol among males, but no change among females. No statistically significant changes in any electro-mechanical muscle activation measures were identified pre-to-post-SMR within either sex. In contrast to the SS literature body, these results suggest that SMR does not influence the electro-mechanical aspects of muscle activation during MVICs. These results provide support for the absence of decreases in force output post-SMR, but further examination regarding the potential muscle mass influence of SMR on electro-mechanical muscle function remains warranted. 2c

Sudden cardiac death (SCD) is the leading type of line-of-duty death among firefighters. An inability to restore parasympathetic nervous system (PSNS) control after activity is associated with SCD. Post-exercise heart rate recovery (HRR) provides unique insight into reactivation of the PSNS. Thus, the purpose of this study was to examine longitudinal changes in HRR responses of 25 male firefighter recruits. HR data were collected after submaximal exercise at week 1 (W1), week 6 (W6), and week 15 (W15) of their training at an academy. Percent maximal heart rate (%MHR) measures were computed at each HRR time point (%MHR₀, %MHR₁₅, %MHR₃₀, %MHR₄₅, %MHR₆₀, %MHR₁₂₀, %MHR₁₈₀) and absolute HRR values were calculated at 30 s (ΔHRR₃₀), 60 s (ΔHRR₆₀), 120 s (ΔHRR₁₂₀), and 180 s (ΔHRR₁₈₀). After controlling for age and percent body fat, there was no statistically significant interaction between Week × HRR (p = 0.730), and there were no changes in ΔHRR₃₀, ΔHRR₆₀, and ΔHRR₁₂₀, and ΔHRR₁₈₀ indices across time. However, %MHR at W6 and W15 was significantly lower than %MHR at W1 at every HRR time point (ps < 0.001). Therefore, although the firefighter recruit training academy elicited positive training adaptations, changes in PSNS reactivation after submaximal activity were not identified.