Acute effects of unilateral static stretching on handgrip strength of the stretched and non-stretched limb.

PURPOSE: To determine the effects of an acute bout of unilateral static stretching on handgrip strength of both the stretched and non-stretched limb. It was reasoned that if the non-stretched limb experienced a decrease in force output, further evidence for a neural mechanism to explain a post-stretch force reduction would be obtained as no mechanical adaptation would have occurred. METHODS: Thirty participants performed maximum voluntary unilateral handgrip contractions of both limbs before and after stretching the finger flexors of the strength-dominant side only. Each trial was assessed for peak force, muscle activity (iEMG), and rate of force generation. RESULTS: Following the stretching bout, peak force and iEMG decreased by 4.4% (p = 0.001) and 6.4% (p = 0.000) respectively in the stretched limb only. However, rate of force generation was significantly impaired in both the stretched (- 17.3%; p = 0.000) and non-stretched limbs (- 10.8%; p = 0.003) 1 min post-stretch, and remained similarly depressed for both limbs 15 min later. CONCLUSION: Acute stretching negatively impacts rate of force generation more than peak force. Moreover, a reduced rate of force generation from the non-stretched limb indicates the presence of a cross-over inhibitory effect through the nervous system, which provides additional evidence for a neural mechanism.

The Influence of Emergency Call Volume on Occupational Workload and Sleep Quality in Urban Firefighters.

OBJECTIVE: The aim of the study is to determine the impact of emergency call volume on exertion, autonomic activity, and sleep among urban structural firefighters. METHODS: Thirty-four firefighters wore a wrist-based monitor to track sleep and autonomic parameters and rated their level of perceived exertion (Borg Rating of Perceived Exertion) and subjective sleepiness after a 24-hour shift. Predictive variables included total run time and total run time after 11:59 PM. RESULTS: Total run time and sleep duration accounted for Borg Rating of Perceived Exertion and subjective sleepiness, while total run time and total run time after 11:59 PM accounted for sleep durations on-duty. CONCLUSIONS: The current results suggest that emergency call volume is associated with indicators of exertion and sleep. As such, call volume tracking is an important consideration for departments to ensure personnel readiness and wellness and provide a method of tracking the occupational demands experienced by firefighters on-duty.

The effect of extended shift work on autonomic function in occupational settings: A systematic review and meta-analysis.

OBJECTIVE: To examine the effect of 24-h shift work on autonomic nervous system function via heart rate variability (HRV) methodologies. METHODS: Electronic databases (indexed in either PubMed, MEDLINE, CINAHL, SPORTDiscus, or OpenDissertations) were searched from January 1964 to March 2023. A modified Downs and Black checklist was used for assessing methodological quality and the Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) approach was used to evaluate the quality of evidence. Study design, study population, study sample, shift work description, and assessment of HRV metrics and methods were extracted from each study. FINDINGS: A total of 58 478 study articles were identified, of which 12 articles met inclusion criteria. Sample sizes varied from eight to 60 participants, with the ratio of low- to high-frequency HRV (LF/HF) as the most common frequency-domain variable reported. Of the nine included studies that observed LF/HF, three (33.3%) demonstrated a significant increase after 24-h shift work. Moreover, of the five studies that reported HF, two (40%) noted a significant decrease after 24-h shift work. When observing risk of bias, two (16.6%) studies were low quality, five (41.7%) were moderate quality, and five (41.7%) were high quality. INTERPRETATION: There were inconsistent findings demonstrating an effect of 24-h shift work on autonomic function, with a suggested shift away from parasympathetic dominance. Discrepancies in HRV methodologies, such as the duration of recordings and hardware used for measurement, may have contributed to the disparity in findings. In addition, differences in roles and responsibilities across occupations may explain the incongruence in findings across studies.