Table 1:

Summary of the exercise training protocols tested during bedrest studies

Publication	Study name Duration of BR Sample size	Exercise modalities	Estimated duration of MVPA	Estimated energy cost
Resistance exercise
Bergouignan A. et al. 2006 Fernandez-Gonzalo R. et al. 2020 Irimia J. et al. 2017 Rudwill F. et al. 2013 Trappe S. et al. 2004	LTBR 2001–2002 90 d HDT-BR n=18 ♂	35 min every 3 d during BR on flywheel ergometer. Progressive warm-up + 4×7 max concentric/eccentric squat + 4×14 in calf press. 2 min rest between sets and 5 min between EX.	82 min MVPA/wk 12 min MVPA/d	8 MET.h/wk 1.2 MET.h/d
Brooks N. et al. 2014	28 d HDT-BR n=31 ♂	1 h/d, 6 d/wk. Target intensity: 70–80% of 1RM as estimated by the OMNI rating of perceived EX 10 category scale. 7 to 8 REX targeting major muscle groups during each session. Lower body (squats, single leg squats, diagonal jump, calf raise, single-leg hip extension, leg curl, single-leg hip abduction) and upper body (pull-ups, pull-over, triceps press, chest fly, shoulder press, biceps curl, upright row, lateral arm raise) EX were performed on alternating days.	360 min MVPA/wk 51 min MVPA/d	36 MET.h/wk 5.2 MET.h/d
Ferrando A. et al. 1997	14 d HDT-BR n=6 ♂	Squat on horizontal leg-training device every 2 d. 3×12 squats, training volume progressively increased to reach 5×8 squat at session 3 till the end of BR.	?	?
Guinet P. et al. 2020 Kenny H. et al. 2017 Kenny H. et al. 2020	MNX 21 d HDT-BR n=12 ♂	5 sessions of EX, on leg press machine with a vibration platform (8 mm peak-to-peak, 25 Hz): bilateral squats (10 rep, 75% 1-RM, 8 s/rep), single heel raises (×1.3 body weight, contractions performed as fast as possible until fatigue) and bilateral heel raises (×1.8 body weight, contractions performed as fast as possible until fatigue). A 5% load adjustment was made based on the ability of volunteers to complete the set of EX.	5–15 min MVPA/wk 0.7–2.1 min MVPA/d	0.5–1.5 MET.h/wk 0.01–0.2 MET.h/d
Moriggi M. et al. 2010	BBR1 55 d HDT-BR n=12 ♂	2 bouts/d of EX (6min each) of RVE at preset frequencies ranging from 19 at the beginning to 25Hz. Total of 89 sessions. 1. Squatting EX: Knees were extended from 90° to almost full extension in cycles of 6s for each squat (knee extensors). 2. Heel raises: With knees almost extended, heels were raised to fatigue. Only then, brief rests (< 5s) were allowed with the entire foot on the vibration platform in order to recover, and subjects started to raise their heels again (foot plantar flexors). 3. Toe raises: Similar to 2, but toes were raised instead of heels (foot dorsi-flexors). 4. “Kicks”: With the same loading as in 1–3, knees were extended as quickly and forcefully as possible. The platform was struck with the balls of the feet, and legs rested on the Galileo Space framework in between the kicks. This was done 10 times with 10s of rest inserted.	36 min MVPA/wk 5.1 min MVPA/d	3.6 MET.h/wk 0.5 MET.h/d
Belavy D. et al 2014 Trudel G. et al. 2012	BBR2–2 60 d HDT-BR n=24 ♂	3 d/wk: 1. Bilateral leg press (~75–80% of pre-bed-rest max voluntary contraction); 2. Dingle-leg heel raises (~1.3 times body weight); 3. Double leg heel raises (~1.8 times body weight); 4. back and forefoot raise (performing hip and lumbar spine extension against gravity with ankle dorsiflexion, but with ~1.5 times body weight applied at the shoulders). The RVE group performed the same exercises as the REX group, except that whole body vibration was applied. The corresponding vibration parameters were as follows: 1. frequency 24 Hz, amplitude 3.5–4 mm, and peak acceleration ~8.7 g, where g ~ 9.81 ms−2; 2. frequency 26 Hz, amplitude 3.5–4 mm, and peak acceleration ~10.2 g; 3. frequency 26 Hz, amplitude 3.5–4 mm, and peak acceleration ~10.2 g; 4. frequency 16 Hz, amplitude 3.5–4 mm, and acceleration ~3.9 g	15.8 min MVPA/wk 2.3 min MVPA/d	1.6 MET.h/wk 0.2 MET.h/d
Combined resistance and aerobic exercise
Bergouignan A. et al., 2009 Bergouignan A. et al., 2010 Lee SM. et al., 2014 Mutin-Carnino M. et al., 2013 Rudwill F. et al., 2015 Salanova M. et al., 2008 Trappe T.A. et al., 2007 Trappe S. et al., 2007 Trappe S. et al., 2008 Trudel G. et al., 2009	WISE 60 d HDT-BR n=16 ♀	REX: 35min every 3 d, 4×7 max concentric/eccentric squat + 4×14 in calf press. AEX: 50min every 2 d, 50min in lower body negative pressure vertical treadmill at 40–80% pre-bedrest VO2max	247 min MVPA/wk 35.3 min MVPA/d	33.1 MET.h/wk 4.7 MET.h/d
Krainski F. et al., 2014	35 d HDT-BR n=27 ♂/♀	REX: 25–30min 2 d/wk. 2×8–12 of lower body exercises (leg press, plantar flexion, knee flexion, hip flexion, and hip abduction) and 1×8–12 of upper body EX (shoulder press, elbow flexion and extension, chest press, pullovers, and abdominal crunches) were performed in the supine position, loads were adjusted weekly to reach muscle fatigue during each set of EX. After 5 wk of BR, 2×20 plantar flexion exercises on each leg 2/d (6–8min) against an elastic band were added for all remaining subjects in EX group. AEX: 6 d/wk. During each week of BR, subjects completed 1 recovery (low intensity, typically <70% max HR), 2 base (moderate intensity, between 70–80% max HR), 1 MSS (vigorous intensity, 80–90% maximal HR), and 2 interval sessions (high intensity, 90–95% max HR or above), each lasting a total of 30 – 46 min and separate warm-up/cool-down phases lasting 5 min each. Intervals consisted of 6 cycles of 3 min at 90–95% of max HR, followed by 3 min at recovery pace.	381 min MVPA/wk 54.4 min MVPA/d	49.5 MET.h/wk 7.1 MET.h/d
Ploutz-Snyder L. et al. 2018	70 d HDT-BR n=26 ♂	REX: 3 d/wk. 3×4 supine lifts (squat, leg press, unilateral leg curl, and heel raise); squats and leg press were each performed using a standard shoulder-width stance, single-leg stance, or wide-leg stance on a rotating basis. Training followed a nonlinear periodized model in which load and repetitions were varied on a daily basis to optimize adaptations. AEX: 6 d/wk. Alternating days of continuous cycle EX for 30 min at 75% of VO2peak (3 d/w) with interval treadmill sessions of 30s, 2min, or 4min intervals (3 d/wk) at nearly max intensity.	314.5 min MVPA/wk 45 min MVPA/d	40 MET.h/wk 5.7 MET.h/d
Ward K. et al. 2020 (In press)	RSL 60 d HDT-BR n=23 ♂	48 sessions including 4 types of training sessions based on varying CMJ and repetitive hops between 80–90% of BW during 1.5–3min preceded by a warm-up and 3 max CMJ at 80% of BW.	17.5 min MVPA/wk 2.5 min MVPA/d	2.6 MET.h/wk 0.4 MET.h/d

HDT-BR: 6° head-down tilt bedrest; d: days; wk: week; max: maximal; BW: body weight; CMJ: countermovement jump; EX: exercise; REX: resistive exercise; AEX: aerobic exercise