From baseline, plasma epinephrine increased 6.3-fold, whereas norepinephrine increased 14.5-fold at the end of sprinting ( Figure 1). examined the catecholamine response of 12 males who completed ten 6-second cycle ergometer sprints with a 30-second recovery between each sprint. found significantly elevated epinephrine and norepinephrine levels after 20 min of HIIE cycle exercise (8 s/12 s and 12 s/24 s protocols) in trained and untrained young women. measured catecholamine response to long (24 s/36 s recovery) and short (6 s/9 s recovery) bout intermittent treadmill exercise and found that norepinephrine was significantly elevated postexercise. Catecholamine response to HIIE protocols that are less intensive than the Wingate protocol have also been shown to be elevated. Catecholamine response has been shown to be significantly elevated after Wingate sprints for both men and women. Hormones that have been shown to increase during HIIE include catecholamines, cortisol, and growth hormones. Heart rate increased to 142 bpm after the first sprint and then increased to 173 bpm following sprint ten. A similar pattern of heart rate response was found for an HIIE protocol consisting of ten 6-second sprints interspersed with 30 s recovery. In this protocol, there is typically a small heart rate decrease of between 5–8 bpm during each 12-second recovery period. Heart rate response to the 8 s/12 s protocol typically averages around 150 bpm after 5 min of HIIE which increases to 170 bpm after 15 min of HIIE. , using the Wingate protocol, recorded peak heart rates of 170 bpm immediately after a 30-second maximal all-out cycle sprint. Heart rate response is dependent on the nature of the HIIE protocol but typically is significantly elevated during exercise and declines during the period between sprint and recovery. Acute Response and Chronic Adaptations to High-Intensity Intermittent ExerciseĪcute responses to HIIE that have been identified include heart rate, hormones, venous blood glucose, and lactate levels, autonomic, and metabolic reactivity. This review summarises results of research examining the effect of different forms of HIIE on fitness, insulin resistance, skeletal muscle, subcutaneous, and abdominal fat loss.Ģ. Thus, one of the characteristics of HIIE is that it involves markedly lower training volume making it a time-efficient strategy to accrue adaptations and possible health benefits compared to traditional aerobic exercise programs. For the HIIE Wingate protocols, total exercise time is typically between 3 to 4 min of total exercise per session. Total sprint time is 8 min with 12 min of low intensity cycling. Thus, instead of 4 to 6 sprints per session, as used in Wingate protocol studies, subjects using the 8 s/12 s protocol sprint 60 times at a lower exercise intensity. For example, we have used an 8-second cycle sprint followed by 12 s of low intensity cycling for a period of 20 min. Other less demanding HIIE protocols have also been utilised. Thus, the Wingate protocol is likely to be unsuitable for most overweight, sedentary individuals interested in losing fat. Insight into the skeletal muscle adaptation to HIIE has mainly been achieved using this type of exercise however, as this protocol is extremely hard, subjects have to be highly motivated to tolerate the accompanying discomfiture. This protocol amounts to 3 to 4 min of exercise per session with each session being typically performed 3 times a week for 2 to 6 weeks. Subjects typically perform the Wingate test 4 to 6 times separated by 4 min of recovery. The most utilized protocol in past research has been the Wingate test which consists of 30 s of all-out sprint with a hard resistance. Subjects studied have included adolescents, young men and women, older individuals, and a number of patient groups. Most commonly the sprints are performed on a stationary cycle ergometer at an intensity in excess of 90% of maximal oxygen uptake ( V ˙ O 2 max ). The length of both the sprint and recovery periods has varied from 6 s to 4 min. HIIE protocols have varied considerably but typically involve repeated brief sprinting at an all-out intensity immediately followed by low intensity exercise or rest. Accumulating evidence suggests that high-intensity intermittent exercise (HIIE) has the potential to be an economical and effective exercise protocol for reducing fat of overweight individuals. Thus, exercise protocols that can be carried out by overweight, inactive individuals that more effectively reduce body fat are required. Disappointingly, these kinds of protocols have led to negligible weight loss. Most exercise protocols designed to induce fat loss have focused on regular steady state exercise such as walking and jogging at a moderate intensity.
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