Ischemic Preconditioning Does Not Improve Time Trial Performance in Recreational Runners

International Journal of Exercise Science 13(6): 1402-1417, 2020. Some evidence indicates that ischemic preconditioning (IPC) may positively affect endurance exercise performance, but IPC’s effect on running performance is unclear. This study’s purpose was to examine the effect of IPC on running performance in recreational runners. Participants (n=12) completed IPC, a sham (SH) condition, and a leg elevation without blood restriction (LE) control condition on separate days (order randomized). For IPC, blood was restricted using blood pressure cuffs inflated to 220 mmHg at the thigh. For SH, the cuffs were inflated to only 20 mmHg. For LE, participants positioned their legs at 90 degrees against a wall while laying supine. The duration of each protocol was 30 minutes (three 5-minute bouts with 5-minute breaks). Following each protocol, participants ran 2.4 kilometers as fast as possible on a motorized treadmill. Run time, heart rate, and perceived exertion were measured and statistically compared, using repeated-measures ANOVA, each 0.8 kilometers. There were no differences in heart rate or time trial performance across protocols (p\u3e0.05; IPC, 612.5±61.2 sec; SH, 608.1±57.9 sec; LE, 612.7±59.1 sec). Rating of perceived exertion at 0.8 kilometers was significantly lower for the IPC protocol than SH in females only (~5.7%, or ~0.8 points on a 6-20 scale; p\u3c0.05). Our IPC protocol did not improve running performance or physiological parameters during a time trial run in recreational runners. The performance benefit seen in this study’s most fit individuals suggests that fitness level may influence IPC’s efficacy for improving endurance running performance

METABOLIC RESPONSES DURING ENDURANCE EXERCISE ANCHORED TO VIGOROUS HEART RATES

BACKGROUND: To improve cardiorespiratory fitness, exercise prescription is often based on percentages of the maximum heart rate (HRmax) or oxygen consumption rate (VO2max) that reflect vigorous intensities (77-95%HRmax, 64-90%VO2max). Adjustments in power output (P) are required during constant HR exercise which results in metabolic rate decreases. This study examined the metabolic (VO2) and P responses during constant HR trials (77, 86, and 95% HRmax) within the vigorous intensity range. METHODS: Fourteen men (mean±SD, age=25.6±4.5yrs) performed a cycle ergometer graded exercise test to determine VO2max, HRmax, and peak power output (PP). Responses were recorded during three constant HR trials at 77%HRmax (138.9±8.4 b·min-1; time to exhaustion [TLim]=56.0±10.1 min, range=25.33-60.0min), 86%HRmax (155.3±9.5 b·min-1; TLim=44.2±19.0 min, range=13.7-60.0min), and 95%HRmax (171.1±10.2 b·min-1; TLim=9.7±7.5 min, range=2.0-26.7min) to exhaustion or up to 60 min. VO2 and power (P) were normalized to their respective values at PP in 10% intervals of TLim. Two-way repeated measures ANOVAs and t-tests with a Bonferroni corrected alpha were used for comparisons across time (p\u3c0.005) and among HR trial intensities (p\u3c0.017) for VO2 and P. Mean values for VO2 across time were qualitatively compared to the corresponding vigorous ranges for each HR trial. RESULTS: There were no time by intensity interactions, but there were main effects for time and intensity for VO2 and P (p\u3c0.05). The VO2 (77%HRmax=56.7±3.8, 86%HRmax=68.1±4.3, 95% HRmax=91.1±3.3%VO2max) and P (77%HRmax=50.4±6.4, 86%HRmax=60.4±7.0, 95% HRmax=77.5±5.7%PP) responses were significantly lower for 77%HRmax relative to 86%HRmax and 95%HRmax, and 86%HRmax was lower than 95%HRmax. Across time, both VO2 and P significantly decreased relative to the initial values from 10%-100%TLim. The mean VO2 responses fell below the recommended VO2 range for vigorous exercise at 10% of TLim for 77%HRmax, and at 90% of TLim for 86%HRmax. The mean VO2 responses remained above the recommended VO2 range for vigorous exercise until 70% of TLim for 95%HRmax. CONCULSIONS: Only the 86%HRmax trial resulted in a vigorous VO2 that was sustained for at least 20 min to meet the current guidelines. To ensure the required metabolic stimulus is met, practitioners and researchers should consider the dissociation between HR and VO2 responses during constant HR exercise

FORCE AND NEUROMUSCULAR RESPONSES DURING CONTINUOUS HANDGRIP HOLDS ANCHORED TO A RATING OF PERCEIVED EXERTION

BACKGROUND: The rating of perceived exertion (RPE)-Clamp Model has been used to examine the interaction between fatigue-induced changes in force and neuromuscular responses when exercise intensity is anchored to a fixed RPE. Neuromuscular responses are commonly described by changes in the amplitude of electromyographic signal (EMG AMP) and neuromuscular efficiency (NME; normalized force divided by normalized EMG AMP)], which provide information about muscle excitation and the level of muscle excitation required to produce a given amount of force, respectively. This study investigated the time course of changes in responses of force, EMG AMP, and NME during a sustained, isometric, handgrip hold to failure (HTF) using the RPE-Clamp Model. METHODS: Twelve men (Mean±SD: 28.2±3.8 yr) performed the handgrip HTF anchored to an RPE of 5 on the 10-point omnibus resistance scale. EMG signals were recorded from the brachioradialis throughout the HTF. Force, EMG AMP, and NME were calculated at standardized segments of 5% of time to task failure (Tlim) and normalized to the respective values from a pre-HTF maximum voluntary isometric contraction (MVIC). Analyses included 1(RPE=5) x 21 (time:0-100% Tlim) repeated measures ANOVAs and post-hoc t-tests with a Bonferroni corrected alpha level (p\u3c0.0025). RESULTS: The Tlim was 512.4±245.9s and the initial normalized force was 25.9±14.3% MVIC. There were significant differences across time for force (F=24.989, p\u3c0.001, η2=0.694), EMG AMP (F=8.416, p\u3c0.001, η2=0.433), NME (F=22.368, p\u3c0.001, η2=0.670). Relative to the initial time point, force decreased from 40% to 100% Tlim, EMG AMP decreased at 30%, 60%, and 100% Tlim, and NME decreased from 50% to 65%, and 80% to 100% Tlim. CONCLUSIONS: The subjects’ initial force selection may be explained by a feedforward mechanism, while a combination of corollary discharges and afferent feedback (i.e., sensory tolerance limit; STL) may explain the continuous decreases in force. Throughout the HTF, muscle excitation (EMG AMP) tracked the force decreases. However, the magnitude of force loss exceeded the magnitude of EMG AMP decreases (↓ NME) indicating greater levels of muscle excitation were required to compensate for the reductions in force generating capacity of fatigued muscle fibers. Task failure may be explained by the individual STL where central motor drive was continuously reduced to maintain the constant RPE