Participants will be recruited to take part in a randomized crossover trial using media advertisements and group events within the Lisbon Metropolitan Area. In order to be part of this intervention, the participants will have to be men or women aged between 65 and 90 years-old, physically active, and engaged in structured exercise at least twice a week for the past 6 months. People who have diabetes or any type of physical limitation that would prevent them from performing exercise will be excluded. Power and sample size calculations (G-Power 3.1.9.2) were based on an effect size of 0.78 for the glucose iAUC, a power of 0.80, and a significance of 0.05. The calculation yielded a sample size of 15 participants. This study was approved by the Ethics Committee of the Faculty of Human Kinetics (approval number: 06/2019) and conducted in accordance with the Declaration of Helsinki and with the Convention on Human Rights and Biomedicine. Written informed consents were obtained from all participants.

Participants will be followed in a randomized crossover trial undertaken at Faculty of Human Kinetics between April and August 2019. Participants will attend the laboratory on twelve separate occasions: visit 1 (day 1), baseline assessments for body composition; visit 2 (day 2), cardiorespiratory fitness assessment; visit 3 (day 3), OGTT and the first randomized experimental protocol; visit 4 (day 4), follow-up OGTT; visit 5 (4-6 days after the first experimental protocol), OGTT and the remaining experimental protocol; visit 6 (day following the previous experimental protocol), follow-up OGTT. An additional 6 visits will be performed following the same rational, after a 2-week period of detraining, where participants will be instructed to refrain from structured exercise and reduce their physical activity. The follow-up assessments for body composition and cardiorespiratory fitness will be accomplished after the protocols. Experimental protocol order will be randomized at baseline and on the follow-up period after the detraining process by a third party using a computer-generated list of random numbers (block randomization with balanced block sizes).

On the morning of each intervention day, participants will arrive at the laboratory at 8:00 a.m., after a 10h fast. For 48h prior to intervention day, participants will be asked to refrain from structured moderate-to-vigorous physical activity (MVPA), caffeine and alcohol consumption. Each intervention day will have a total duration of 9.5h and will start with an oral glucose tolerance test. After a baseline blood collection, participants will be instructed to drink an oral glucose drink of 75g dissolved in water (200 ml). Two hours after, another blood sample will be drawn.

At 10:30 a.m., a mixed standard meal (breakfast) will be given to the participants, marking the begging of the 7 hour protocol. The same standard meal will be provided at 1:30 p.m. (lunch). The 200-ml meal will consist of 303 kcal, 42g carbohydrate, 10g fat and 11.2g protein, vitamins and minerals (Nestle Health Science - Resource Energy). The participants will be encouraged to consume the entire meal within 5 minutes. The protocols performed will be: 1) uninterrupted sitting: participants will remain seated throughout 7 hours (SIT); 2) Sitting + moderate intensity breaks: participants will be instructed to sit throughout 7 hours, while interrupting the sitting position every 30 minutes to perform 2 minutes of moderate-intensity physical activity. The breaks will consist of walk up and down the stairs and squats. Each person will perform these exercises alternately. During the protocol, participants will be allowed to go to the bathroom in a wheelchair and al-libitum water will be granted. The following morning after the protocol, the OGTT will be repeated.