The effect of fitness level on cardiac autonomic regulation, IL-6,total antioxidant capacity, and muscle damage responses to a single bout of high-intensity interval training

Purpose:The aim of this study was to investigate the influence of the cardiorespiratory fitness level on the response to high-intensity interval training(HIIT)with an individually adjusted running speed of the same relative intensity.The evaluation focused on acute cardiorespiratory response,postexercise cardiac autonomic modulation(heart rate variability(HRV))and biochemical markers of inflammation,oxidative stress,and muscle damage.Methods:Thirty participants were divided into 3 subgroups:well trained,moderately trained,and untrained.All the participants performed30 min HIIT composed of 6×2 min interval exercise with work-to-relief ratio=1 and work intensity 100%of individual velocity at maximal oxygen consumption(VO2max).Acute cardiorespiratory variables,postexercise HRV,lactate,interleukin-6(IL-6),total antioxidant capacity(TAC),creatine kinase,and myoglobin up to 4h after HIIT were monitored.Results:The differences in relatively expressed cardiorespiratory variables(heart rate,VO2)during HIIT were at most moderate,with the most pronounced between-group differences in absolute VO2 values.The disruption of the postexercise HRV was the most pronounced in untrained individuals,and this difference persisted 1 h after HIIT.The highest postexercise IL-6 and TAC concentrations and the lowest changes in creatine kinase and myoglobin were revealed in well-trained individuals.Conclusion:The higher fitness level was associated with the less pronounced postexercise cardiac autonomic changes and their faster restoration,even when there were similar acute cardiorespiratory responses.These findings were simultaneously accompanied by the higher postexercise IL-6 and TAC concentrations and less significant changes in muscle damage biochemical markers in well-trained individuals.

Footfall patterns of a runner with an Achilles tendon rupture

Purpose: This study aims to compare the load and the length of previously ruptured and healthy Achilles tendon(AT) of a recreational runner who used different footfall patterns on each limb during running.Methods: A 41-year-old recreational athlete with a ruptured AT participated in this report. Two force plates and a high-speed motion capture system were used to collect ground reaction force and kinematic data in shod and barefoot running conditions. AT length was measured using ultrasonography and an infrared camera system. AT force was estimated as the active plantar flexion moment divided by AT moment arm during stance phase.Results: The participant used a rearfoot pattern on the affected limb and a forefoot/midfoot pattern on the unaffected limb during shod running,and a forefoot/midfoot pattern during barefoot running. There was no difference between the length of the affected and the unaffected AT. During shod running, the maximal AT force and loading rate were lower in the affected AT versus the unaffected AT. During barefoot running, the affected maximal AT force and loading rate were greater than the unaffected AT.Conclusion: Footfall patterns can be an adaptation to reduce the loading on a previously injured AT. It appears that runners may consider using a rearfoot footfall pattern during running to reduce the stress on the AT.