Exercise training is a cornerstone for the prevention and treatment of metabolic disorders and associated cardiometabolic complications such as type 2 diabetes mellitus (T2D) and hypertension. Similar to the beneficial health effects after performing conventional continuous exercise modalities, high intensity interval training (HIIT) has been reported as an effective alternative exercise-modality to improve glucose homeostasis in both prediabetes subjects and individuals with T2D diagnosed. In this regard, although multiple HIIT-based interventions commonly report acute and long term benefits on body composition, cardiorespiratory fitness and insulin sensitivity in metabolically compromised subjects, little is known about the acute cardiovascular response (i.e., at heart rate level) during HIIT in subjects with different glucose control.

HIIT is described as performing brief periods of exercise at vigorous or maximal intensity, interspersed with inactive or low intensity recovery phases of variable duration. In order to characterize different HIIT-based protocols, exercise intensity is usually defined as relative percentages of individual maximal cardiorespiratory fitness (VO2max) or relative maximal power output values. Nevertheless, the need for specific technological equipment to assess these parameters usually limit the prescription and recommendations of HIIT in clinical settings and other public health contexts at massive level. Additionally, the use of self-perceived exertion scales and heart rate (HR) variations upon HIIT have been demonstrating to be accessible and feasible strategies to regulate exercise intensity during HIIT. For example, it was reported that HR and self-perceived exertion scores increased progressively in T2D subjects, parallel to the oxygen consumption rate throughout an acute HIIT session performed on cycle ergometer. Consequently, it is conceivable to hypothesize that determining HR variations during HIIT might optimize the recommendation of this training methodology in metabolically compromised subjects as those at risk or with T2D diagnosed. Therefore, the aim of the present study was To describe and compare the acute heart rate changes in response to an incremental maximal exercise test and a single HIIT session between normoglycaemic (NG), prediabetes (Pre-T2D) and type 2 diabetes mellitus (T2D) subjects.

This cross-sectional study will use a non-probabilistic sample of 75 adult subjects, characterized as healthy normoglycaemic and others with disturbed glucose homeostasis subjects, all referred by a physician to the exercise programme of our research centre. The present study will be carried out in accordance with the Declaration of Helsinki and was approved by the Scientific Ethics Committee of the Universidad de La Frontera. All volunteers read and signed an informed consent. The inclusion criteria will be; a) aged 18-60 y; b) previously screened by physician professional; c) diagnosed with normoglycaemic, prediabetes or T2D state; d) and living in Temuco city. The exclusion criteria will be; a) low maximal cardiorespiratory fitness (defined as VO2max ≤21 ml/kg-1/min-1) below the expected value for the subject's sex and age 11; b) not receiving pharmacologic hypotensive treatment with β-blockers; and c) having no musculoskeletal limitations to perform exercise cycling. The total sample size will be divided in three groups according to the standard glycaemic classification 12; normoglycaemic (NG, n = 32), pre-diabetes (Pre-T2D, n = 30) and type 2 diabetes (T2D, n = 13). The study considered three stages of measurements (enrollment, exercise test, single HIIT session).

Inclusion Criteria:

• aged 18-60 y
• previously screened by physician professional
• diagnosed with normoglycaemic, prediabetes or T2D state
• living in Temuco city

Exclusion Criteria:

• low maximal cardiorespiratory fitness (defined as VO2max ≤21 ml/kg-1/min-1) below the expected value for the subject's sex and age
• not receiving pharmacologic hypotensive treatment with β-blockers
• having no musculoskeletal limitations to perform exercise cycling

We hope to send data of individual participant according with requirements by e-mail.

The exercise session consisted of 1-minute cycling at high intensity (workload during each interval was set at ~80-100 % maximal power (i.e., load in Watts) achieved during the incremental exercise test with a workload that allowed to work until the volitional muscle failure in 1-minute), followed by 2-minutes of inactive resting period (sitting still on the cycle ergometer), and was repeated 10 times (1x2x10 protocol; 1:2:10 to work:rest:repetitions respectively). The exercise session was supervised individually by exercise professionals, monitoring the heart rate with a continuous telemetric heart rate sensor (Polar FT4, PolarTM, Finland). During the single HIIT session, the HR pre each interval (HR-preINT) and the HR post each interval (HR-postINT) of cycling was recorded individually. In addition, we calculated and report the percentage of maximum heart rate in each interval, delta of HR increment and delta HR recovery for each 10-interval HIIT are reported.