Respiratory responses to exercise in older and younger adults

Participants will attend the laboratory on three separate occasions. Visits 2 is generally 1-2 weeks after visit 1, while the second and third visits will be separated by at least 24 hours and completed within 1 week. Each visit will be held at approximately the same time of day. All aspects of the intervention will be administered by university research students or university researchers. There is no difference in experimental procedure for the control and intervention group (we are reviewing whether they respond differently to the same stimulus). During visit 1, participants will complete their medical and consent forms. Participants will then be asked to self-report on their dyspnoea using the Medical Research Council dyspnoea scale. Following this their height, body mass and lung function will be measured. Subsequently, participants will have an electrocardiogram (ECG) at rest which will be sent to a cardiologist for review. Participants will not be permitted to participate in the project without the permission of the cardiologist. Participants will subsequently be familiarised with all the other experimental procedures required for testing. During visit 2, participants will complete maximal inspiratory and expiratory mouth pressure manoeuvres, as well as forced vital capacity and inspiratory capacity manoeuvres. Maximal inspiratory pressure manoeuvre require participants to breath out fully, before breathing in maximally against an occluded mouthpiece. Maximal expiratory manoeuvre requires participants to take a full breath in and then then breath out maximally against an occluded mouthpiece. Forced vital capacity manoeuvre requires participants to take a maximally deep breath in, followed by a maximally forceful breath out which is sustained for 6 second. Inspiratory capacity manoeuvre requires participants to inspire maximally at the end of a normal breath out. Participants will then complete an incremental cycling test (Corival; Lode, Groningen, Netherlands) to the limit of volitional tolerance. The cycling test commences with exercise at either 60, 80 or 100 W with increases of 20 W in two minute stages. The starting power depends on self-reported participant fitness (Coffman, Carlson, Miller, Johnson, & Taylor, 2017). During visit 3, participants will again perform forced vital capacity and inspiratory capacity manoeuvres as well as supramaximal cervical and thoracic magnetic stimulation (delivered using Magstim 90mm remote coil and Magstim BiStim2 set to single pulse). The stimulations are carried out as so, participants have a magnetic stimulator placed over the cervical vertebrae and a magnetic stimulation is delivered. Thoracic stimulation is carried out similarly, except the stimulator is placed over the thoracic vertebrae. Stimulation duration's are approximately 1-2ms. Stimulations are performed before the exercise tolerance test, immediately after the test, 15minutes after the test and 30 minutes after the test. After the first set of stimulations are complete participants will undertake the exercise tolerance test (cycling at 85% of their maximum power output until the limit of volitional tolerance). Immediately, 15 and 30min post test participants will complete further sets of stimulations. Each cycling test will begin with 5 minutes of steady state rest (the participant will be seated on the bike and undertaking no activity), followed by a 1 minute warm up of unloaded pedalling (self-paced cycling with at 0 W). During visits 2 and 3, participants will have the catheter inserted and positioned in their oesophagus and stomach. The participants will then be connected to an electrocardiogram (ECG) monitoring system and a pulse oximeter, as well as having electromyography (EMG) electrodes attached to their scalene and parasternal muscles. The ECG and pulse oximetry signals will be monitored during the exercise to minimise chances of participants experiencing a cardiac event. At rest, every 2 minutes, and at the end of the exercise tests, participants will complete inspiratory capacity manoeuvres for EMG normalisation and to calculate end-expiratory and end-inspiratory lung volumes (operating lung volumes). At the same time points, rating of perceived exertion (RPE) for leg and breathing discomfort will be assessed using Borgs CR10 scale. Additionally, at the end of exercise, participants will be asked to: state their primary reason for stopping exercise (e.g., leg discomfort or breathing discomfort); give and RPE value for leg and breathing discomfort (Borg Scale); and complete the qualitative descriptors of dyspnea at symptom limitation questionnaire. The comparator (65-84 years) and control group (18-35 years) follow the same intervention procedure (i.e., both groups follow the procedure described above).