title: THE EFFECT OF INTERVAL DURATION AND WORK-TO-REST RATIO ON ACUTE PHYSIOLOGICAL AND PERCEPTUAL RESPONSES, AND CARDIORESPIRATORY FITNESS FOLLOWING A HOME-BASED HIIT TRAINING INTERVENTION
Creators: name: Church, H
Publisher: name: Liverpool John Moores University
Year: 2021

description: Introduction: Laboratory-based High intensity interval training (HIIT) is an efficacious time-saving exercise modality resulting in similar adaptations to traditional moderate-intensity continuous training. Recently, Home-based HIIT, involving bodyweight exercises, has gained popularity in the literature, as it overcomes additional barriers such as limited access to facilities and appropriate equipment. However, literature in to home-based HIIT is still sparse, and little is known about how manipulating interval duration, interval number and work-to-rest ratio could influence the efficacy and effectiveness of such interventions. Aims: Two separate but related studies were conducted. The aim of study 1 was to investigate the acute physiological, perceptual, and motivational responses to five home-based HIIT protocols with various work-to-rest ratios (specifically 1:1, 1:2 and 1:4) and interval durations (30s or 60s). The aim of study 2 was to implement and compare two of the HIIT protocols investigated in study one to identify the ideal interval duration for improving cardiorespiratory fitness (CRF) and health in sedentary individuals. Methods: In Study 1, 10 healthy participants (age = 25±4 yrs, BMI = 22.7±1.4kg.m2) completed a randomised cross-over study, whereby each participant completed five bodyweight HIIT protocols, four using 30s intervals (30:30x6 (30s interval interspersed with 30s rest, completed 6 times), 30:60x6, 30:120x6 and 30:30x12) and one using 60s intervals (60:60x6). A total of 12 exercises were implemented, examples included burpees, mountain climbers, and jumping jacks. Blood lactate, heart rate (HR), feeling scale (FS), enjoyment and perceived competence were measured in response to each protocol. In Study 2, 28 healthy sedentary participants (age = 29±10 yrs, BMI = 25.3±3.9 kg.m2) completed a randomised cross-over design, whereby each participant completed 6 weeks of 30:120HIIT (4-8x30s with 120s rest) and 60:60HIIT (6-10x60s with 60s rest). In addition to the 12 exercises implemented in study 1, a further 6 were added in study 2. CRF, body composition (bioimpedance), blood pressure and aortic pulse wave velocity were assessed pre and post each intervention, with a 4-6-week wash-out period between interventions. Results: Study 1 (acute phase), established that 60:60x6 and 30:30x12 resulted in significantly higher change in blood lactate and HR responses compared to 30:30x6, 30:60x6, and 30:120x6 (P&lt;0.05). 30:120x6 had a significantly higher minimum reported feeling scale score compared to all other protocols (P&lt;0.05). No significant differences were reported for interest/enjoyment or perceived competence between protocols (P&gt;0.05). Study 2 (chronic phase) demonstrated that CRF increased following both 30:120HIIT and 60:60HIIT (P&lt;0.05). There was a significant reduction in aPWV following 30:120HIIT and 60:60HIIT (P&lt;0.05). Systolic BP decreased significantly in 30:120HIIT with no difference in 60:60HIIT (P=0.414). Magnitude of change between protocols was not different for any of the measured variables (P&gt;0.05). Conclusion: This is the first study to directly compare different home-based HIIT protocols by manipulating interval durations and work-to-rest ratios. Home-based HIIT protocols consisting of 30:120HIIT and 60:60HIIT improved CRF and aPWV after 6 weeks in sedentary individuals, despite 30:120HIIT producing significantly lower lactate and heart rate responses whilst also showing less aversive perceptions during an acute bout of exercise to that of 60:60HIIT.