Several studies have shown that high intensity intermittent sprints (HIIS) are more effective than moderate intensity continuous cycling (MICC) in reducing fat mass and improving insulin resistance in normal weight individuals. Changes in the appetite-regulatory system in response to exercise are likely to explain, at least partially, the better outcome observed after HIIS. Unfortunately, there are no studies comparing the impact of different types of acute aerobic exercise on the release of appetite-regulating hormones, subjective feelings of appetite and subsequent energy intake (EI).

The primary objective of this study is to investigate the effects of acute isocaloric bouts of HIIT and MICC or a short duration sprint, in comparison with a resting control condition, on the postprandial release of appetite-regulating hormones, subjective feelings of appetite and subsequent EI in obese individuals. The investigators hypothesize that an isocaloric session of HIIS will result in a better short-term appetite control compared with MICC, by reducing hunger feelings and subsequent food intake more than MICC and by inducing a larger increase in the release of satiety gut peptides compared with the MICC.

This will be a randomised cross-over study with four legs. Participants will act as their own controls and will be assigned to the four experimental conditions (resting, HIIS, MICC and SDS), 1 week apart, in a counter-balanced order.

Participants will be asked to come to the Unit five times: one preliminary session and four experimental conditions (resting, HIIS and MICC isocaloric sessions and SDS). In the preliminary session, anthropometric data (weight and height) will be collected and a maximal fitness test performed, using a cycle ergometer.

For the four experimental conditions, participants will be asked to arrive at approximately 8.00, having fasted for at least 10 hours, and a cannula will be inserted into an antecubital vein. Two fasting blood samples will be taken and a standard breakfast offered. After that, serial blood samples will be taken at regular intervals for a period of 3h.

Participants will be asked to rate their subjective feelings of hunger and fullness using visual analogue scales (VAS) throughout each study morning at different time points. Three hours after breakfast, participants will be placed in individual rooms, presented with a standardized lunch and instructed to rate the taste and palatability of the food presented.

Inclusion Criteria:

• an inactive lifestyle,
• weight stable on the previous 3 months,
• not currently dieting to loose weight
• restraint score derived from the Three Factor Eating Behaviour Questionnaire ≤12

Exclusion Criteria:

• history of coronary heart disease,
• type 1 or type 2 diabetes,
• anaemia,
• gout,
• depression or other psychological disorders,
• eating disorders,
• drug or alcohol abuse within the last two years,
• current medication known to affect appetite or induce weight loss and hypertension.