Determining the effects of short-term resistance exercise on muscle growth responses prior to an acute period of step-reduction physical inactivity between females and males aged 18-25 years

This study will assess whether three sessions of 'prehab' resistance exercise resist declines in muscle of protein synthesis prior to a 7-day period of step-reduction physical inactivity. All participants will complete 10 separate visits (outlined below) over the entire duration of a 3-to-4-week period. Visit 1: This visit will last for approximately 1-1.5 hours and will involve a tour of the facilities at Swinburne University by the research investigators as well as completion of the following tasks: (1) Sign Consent Information Statement; (2) Testing of strength capacity with a 1-RM (repetition maximum) leg press and leg extension test that will last for approximately 45-60 minutes (one-on-one with research investigators. Following a 5-minute warm up on a treadmill or stationary bike, participants will undertake the strength test unilaterally (i.e.: one-legged) on both legs and involve participants informing the research investigators of their ‘rate of perceived exertion’ using a 1-10 scale indicating the level of difficulty in performing a single repetition for each of the listed exercises. Small weight increments will gradually be added to the Leg Press and Leg Extension machine until participants record a score of a 9 or 10 on the ‘rate of perceived’ exertion scale. Participants will be given a 3–4-minute rest period between attempts and will be supported and coached by the research team who have exercise training experience Visit 2 (approximately 3 days to 7 days after Visit 1): Participants will be provided with an accelerometer to wear for the next 7 days. Participants will be advised to maintain their habitual (usual) step count/daily activity excluding any other form of exercise (e.g. gym, Pilates/yoga, sporting programs etc.). Visit 3 (7 days after Visit 2): Participants will meet one-on-one with research investigators (one-on-one) at Swinburne University to have their body composition measurements taken via a Bioelectrical Impedance Scale as well as a muscle ultrasound on the upper region of their leg (quadriceps muscle) to determine how muscle thickness may have changed over the course of the study period. Participants will be given their ‘loading’ dose of deuterated water (D2O). D2O is orally ingested and is used as part of this research project to measure muscle growth responses. The amount of deuterated water provided to participants will depend on their fat free (total muscle) mass. The researchers will use a calculation based on this measurement to determine how many millilitres a participant will be required to consume in 4 lots each 2 hours for a period of 8 hours. Specifically, participants will consume 8 doses of 0.625 ml/kg Fat Free Mass 70% D2O over the course of an 8 hour period. Each day for the remainder of the study, participants will be required to consume a ‘maintenance’ volume of D2O, which will be calculated according to their muscle mass. The researchers will provide participant’s a bottle containing the correct amount to be consumed each day. Specifically, participants will consume 1 dose of 0.625 ml/kg FFM 70% D2O daily for their maintenance dose. Finally, participants will be provided a standardised meal pack prepared by the researchers. This meal will be consumed in the evening of that day, and participants will then fast for a period of 12 hours overnight. Standardised meals will be prepared by an Accredited Practising Dietitian and will contain a meal consisting of 65% carbohydrate, 15% protein, and 20% fat based on body weight. Examples of components of this meal include: Tasti™ protein muesli bar (1 to 2 bars), Banana, Woolworths chicken satay or Bolognese, Chobani yoghurt, Two-fruits in jelly. Visit 4 (next day from Visit 3): Participants will meet the research team at Victoria University and have a 5ml blood sample taken from the ante-cubital vein in their arm (inside side of the elbow) via venepuncture. A single muscle biopsy will be taken from either the left or right outer thigh muscle (quadriceps) by a Medical Doctor using standardised procedures performed multiple times previously by the research team. Briefly, in preparation for a muscle biopsy, a small amount of local anaesthetic is injected under the skin on the outside of the upper thigh area. A small, 4-5 mm incision is then made into the skin to create an opening for the biopsy needle. The biopsy needle is then inserted through the incision site. After each biopsy, the incision will be closed with sterile tape and wrapped with a bandage. Visits 5 (next day from Visit 4), 6, and 7: For these visits, participants will be required to arrive at the strength laboratory at Swinburne University where they will perform a one-legged resistance exercise bout consisting of 5 x 10 repetitions performed at 80% of the participants 1-RM (~8/10 on a Rate of Perceived Exertion scale) with a 3 min recovery between sets. Both Leg Extension and Leg Press machine exercises will be performed on each of these visits (one-on-one between participant and research investigators). Each of these exercise sessions will be performed on the same leg to maintain consistency. All sessions will be supervised by members of the research team with exercise training experience. As with Visit 3, participants will be provided a standardised meal pack prepared by the researchers. This meal will be consumed in the evening of that day, and participants will then fast for a period of 12 hours overnight. Visit 8 (next day from Visit 7): Participants will meet the research team at Victoria University and have a 5ml blood sample taken from the ante-cubital vein in their arm (inside side of the elbow) via venepuncture. Additionally, a muscle biopsy will be taken from both the left and right outer thigh muscle (quadriceps) by a Medical Doctor (one-on-one) using standardised procedures performed multiple times previously by the research team. As with Visit 2, participants will be provided with an accelerometer to wear for the next 7 days. From the following/next day to Visit 9, participants will be advised to reduce their daily step count to 1,500 steps per day. Participants will still live freely within their home environment and live recordings of participant step count will be accessible to the research team via the accelerometer provided to participants. During this 7-day period, participants will be provided online vouchers for purchasing food to be delivered to their home address. As with Visits 3 and 5, participants will also be provided a participants will be provided a standardised meal pack prepared by the researchers. This meal will be consumed in the evening prior to Visit 9, and participants will then fast for a period of 12 hours overnight. Visit 9 (7 days after Visit 8): Participants will meet the research team at Victoria University and have a 5ml blood sample taken from the ante-cubital vein in their arm (inside side of the elbow) via venepuncture (one-on-one between participant and research investigators).). Additionally, a muscle biopsy will be taken from both the left and right outer thigh muscle (quadriceps) by a Medical Doctor using standardised procedures performed multiple times previously by the research team. Visit 10 (next day from Visit 9): Participants will meet with research investigators to undergo a 1-RM (repetition maximum) leg press and leg extension test as undertaken on Visit 1. Also on this day, participants will undergo measures of their body composition and muscle ultrasound as outlined on Visit 3 (one-on-one between participant and research investigators).