Effects of Heart Rate Biofeedback, Sleep, and Alertness on Marksmanship Accuracy during a Live-fire Stress Shoot.

On the job, law enforcement may be required to utilize lethal force to maintain personal or public safety. Officers' attention to detail, decision-making, and marksmanship accuracy (MA) may be impaired by reduced sleep, increased heart rate (HR), and breathing rate (BR). HR biofeedback (emWave, EW) may help mitigate these impairments. This study sought to determine the impact EW had on MA, stress shoot time-to-completion (TTC), HR and BR versus placebo (PLA). Ten activeduty police officers volunteered for this study. Officers completed two live-fire stress shoots on a 25-m gun range (i.e., familiarization, followed by EW, or PLA trials). MA was assessed as "hit, no-hit." HR and BR were monitored before, immediately after, and 20 minutes post-trial. Sleep was monitored during the entirety of the study. Dependent t-tests were conducted for MA and TTC. A 2x3 repeated-measures ANOVA was conducted for HR, BR, before, during, and after each trial. There were no statistical differences (EW vs. PLA) for: HR (128 ± 23 vs. 136 ± 14; p = 0.30), BR (19 ± 2 vs. 21 ± 2; p = 0.31), TTC (108.4 ± 11.2s vs. 111.6 ± 20.2s; p = 0.94; d = 0.21). Alertness (83.2 ± 9.5 vs. 77.9 ± 15.5), was not statistically significant EW vs. PLA (p = 0.32; d = 0.42). MA (81.4 ± 10.2 vs. 85.9 ± 12.9%) was not statistically significant EW vs. PLA (p = 0.95; d = 0.38). Sleep (7.4 ± 2.9h vs. 5.4 ± 1.7h) was not statistically significant EW vs. PLA (p = 0.13; d = 1.0). EW usage did not affect the physiological and marksmanship performance of officers during a live-fire stress shoot based on HR, BR, TTC, and MA while considering sleep quantity.

The effect of extrinsic factors on simulated 20-km time trial performance.

During time trials cyclists start individually with a uniform time gap between riders. With the exception of the first and last cyclists all riders will chase riders ahead and be chased from behind. The purpose of this study was to determine if cycling in a lead or chase position would influence 20-km time trial performance. Eight male cyclists performed four 20-km indoor time trials. During trial 1 (T1) individuals cycled as fast as possible. Prior to the start of trial 2 (T2) subjects were shown times and rank order from T1 and attempted to improve rank among opponents. After T2 subjects were ranked again and paired with the closest competitor. Subjects were alternately positioned to lead (TL) and chase (TC) in trials 3 and 4. TL and TC were counterbalanced. Means for time, mean power (MP), ratings of perceived exertion (RPE), and heart rate (HR) were recorded and pacing evenness was compared between trials using deviation scores (power variation at designated distances from overall mean). Repeated-measures analysis of variance (ANOVA) (alpha = 0.05) indicated no significant differences for HR or RPE. For time, T2 (33.84 ± 1.38 minutes) was significantly faster than T1 (34.80 ± 2.25 minutes) and MP was significantly greater (T1 = 229 ± 36 W, T2 = 243 ± 24 W). Time for TC (33.52 ± 1.33 minutes) was significantly faster than T1 (34.80 ± 2.25 minutes). Pacing during TC (9 ± 3 W) was significantly more even in comparison to TL (12 ± 1 W). No significant difference in performance was detected between TC and TL. In conclusion, extrinsic factors (chase vs. lead position) did not affect overall performance, even when pacing altered between trials; however, differences in performance times may represent meaningful differences in competitive settings.

Effects of saddle height on economy in cycling.

Research has demonstrated that properly adjusting saddle height is important for both performance and injury prevention during cycling. Peer-reviewed literature recommends the use of a 25 degrees to 35 degrees knee angle for injury prevention and 109% of inseam for optimal performance. Previous research has established that these 2 methods do not produce similar saddle heights. Previous research has also compared anaerobic power among a 25 degrees knee angle, a 35 degrees knee angle, and 109% of inseam and found an increase in anaerobic power at a 25 degrees knee angle. While anaerobic power production has been compared between these 2 methods, aerobic power and economy have not been. The purpose of this study was to determine the difference in economy between these 2 methods of adjusting saddle height. Fifteen subjects, consisting of 5 cyclists (all men) and 10 noncyclists (2 men and 8 women), participated in this study. A graded exercise protocol was utilized in order to determine intensity for the remaining trials. On the last 3 trials, subjects rode for 15 minutes at the resistance at which they reached 70% of Vo2max on a cycle ergometer. Vo2, heart rate (HR), and rating of perceived exertion (RPE) were compared to detect differences in economy between saddle heights. No significant differences were noted in HR or RPE. Vo2 was found to be significantly lower at a saddle height set with a 25 degrees knee angle when compared to a 35 degrees knee angle and 109% of inseam. Findings from this study support the use of a 25 degrees knee angle for both performance and injury prevention.

Effects of saddle height on anaerobic power production in cycling.

In competitive cycling, setting the proper saddle height is important for both performance and injury prevention. This is also true for ergometer use in a laboratory. The cycling literature recommends using a 25 to 35 degrees knee angle to set saddle height for injury prevention and recommends using 109% of inseam length for optimal performance. Prior research has demonstrated that these 2 methods do not produce similar saddle heights. The purpose of this study was to determine if there is a difference in performance between these 2 methods. Trained cyclists (n = 9) and noncyclists (n = 18) participated in this study. Anaerobic power production was compared using a 30s Wingate protocol at a saddle height of 109% of inseam and at 25 and 35 degrees knee angles. Saddle height set using 109% of inseam fell outside the recommended 25 to 35 degrees knee angle 63% of the time. There were no significant differences (p > 0.05) for peak power and mean power in either group between saddle heights. The data when using 109% to set saddle height were then divided into those that fell within the recommended 25 to 35 degrees knee angle and those that fell outside. A 25 degrees knee angle produced a significantly higher mean power compared with 109% in those that fell outside the recommended range. An increase in power, at a 25 degrees angle, can be extrapolated to increased performance. There was no difference in performance detected in those individuals who fell within the recommended range. For this reason it is recommended that saddle height for cycles and ergometers be set using a 25 to 35 degrees knee angle for both trained and untrained cyclists for both injury prevention and increased performance.