An Evidence-Based 

Approach To Exercise 

Prescriptions on ISS

Lori Ploutz-Snyder, Ph.D

Project Scientist & Lab Manager

Exercise Physiology and Countermeasures

Universities Space Research Association

Lyndon B Johnson Space Center

Summary of the Presentation

– Current exercise countermeasures

– New ISS exercise equipment

– Strategy for evaluation of evidence

– Proposed new ExRx

Historic ISS Exercise

•

2.5 hrs/day, 6 days/wk

•

Resistance exercise

–

iRED

–

Predominantly high reps low loads

•

Aerobic exercise

–

TVIS & CEVIS

–

30 min continuous at ~70% HRmax

–

Some  interval work – “Greenleaf protocol”

Limitations of ISS Exercise Hardware

•

iRED

–

Maximal load 300 lbs

–

Elastic bungee resistance

not constant

–

Limited eccentric 

component

Limitations of ISS Exercise Hardware

•

CEVIS

–

Maximal load 300 Watts

•

TVIS

–

Speed limitations

–

Subject loading limitations

Limitations of ISS Exercise Hardware

•

TVIS

–

Speed limitations

–

Subject loading limitations

Fitness Changes on ISS

•

ISS crewmembers 

(expeditions 1-15, n=18)

–

Isokinetic knee extensor 

and flexor strength decrease

11% and 17%, respectively. 

–

Isokinetic knee extensor and flexor endurance 
decrease 10% and 9%. 

–

Maximal aerobic capacity (estimated from 
submaximal test) 10% reduction 

–

Bone mineral density (BMD) 2-7% decrease 
depending on site. 

Why?

•

ISS exercise hardware does not allow 
for sufficient intensity of exercise

•

Inadequate ExRx

•

Crew member noncompliance with 
ExRx

•

Other

New ISS Hardware - ARED

•

More exercises (29 different ones)

•

Instrumented for data acquisition 

–

Sets

–

Reps

–

Ground reaction forces 

–

Load at the bar

•

Improved  loading

–

600 lbs

–

Ecc-Con Ratio ~90%

–

Constant load

–

Simulated inertia (free weight)

New ISS Hardware – T2

•

Better harness & subject loading system

•

Instrumented to record ground reaction 

force

•

Improved speed

HRP Integrated Research Plan 

Risks and Gaps

•

Risk of impaired performance due to reduced muscle 
mass, strength and endurance.

–

Gap M7: Can the current in-flight performance be maintained 
with reduced exercise volume?

–

Gap M8: What is the minimum exercise regimens needed to 
maintain fitness levels for tasks?

–

Gap M9: What is the minimum set of exercise hardware needed 
to maintain those (M8) levels?

•

Risk of reduced physical performance capabilities due to 
reduced aerobic capacity.

–

Gaps M7-9: (above)

–

Gap M2: What is the current status of in-flight and post-flight 
performance capability?

–

Gap CV2: What is VO

2max

in-flight and immediately post-flight?

More Risks/Gaps

•

Risk of accelerated osteoporosis.

–

Gap B15: Can exercise hardware and 
protocol be designed to provide loads 
necessary to maintain bone health?

Workshops

•

June and October 2008 workshops suggested 
enough ground-based evidence existed to move 
forward with a flight ExRx study.

–

ASCR, ExPC, HRP management, flight surgeons, medical 
operations, external experts

•

Major recommendations

–

Higher intensity, less frequent resistance exercise

–

More variety of resistance exercises

–

Alternate days of moderate intensity continuous aerobic 
exercise with higher intensity interval aerobic exercise 

–

Monitor in-flight exercise performance using instrumented 
hardware

–

Include more robust physiological outcome measurements to 
document the efficacy of the exercise program.

•

March 2009 proposal submitted for NAR

Strategy for ExRx

•

Identify exercise training programs that have been 
shown to maximize adaptive benefits of people 
exercising in both 0 and 1 g environments. 

•

Priority order of evidence

–

ISS  or spaceflight information

–

Human flight analog studies (bedrest, unilateral lower limb 
suspension (ULLS). 

–

Human 1-g exercise training studies

–

Animal flight analogs or 1 g studies

only in the rare 

cases where no human data exist. 

Cardiovascular Fitness

•

“Capacity of the heart and lungs to 
supply oxygen-rich blood to the working 
muscles 

and

the capacity of the 

muscles to use oxygen to produce 
energy.”

www.health.qld.gov.au/npag/glossary.asp

•

Evaluation should include more than 
VO

2

max

Intensity Is The Key Factor

•

Trained for 10 weeks 

–

High intensity (90-100% max HR) interval 
cycle (6x 5min, 2 min rest) exercise 
alternated with continuous running as fast 
as possible for 40 min.

•

Divided subjects into 3 maintenance 
groups where one factor was reduced: 
intensity, duration or frequency.

(Hickson et al, 1981, 1982, 1985

)

Maintenance Groups

•

Intensity

–

Work rate reduced by 1/3 or 2/3

•

Duration

–

Reduced from 40 to 26 or 13 min/day

•

Frequency

–

Reduced from 6 to 4 or 2 days/week

(Hickson et al, 1981, 1982, 1985)

Which Group Would You Choose?

•

Physiological adaptations were most robust to a 

decrease in training frequency

as evidenced by a 

maintained VO

2

max with as little as 2 days/week of 

high intensity exercise.

•

Most physiological adaptations were maintained 
despite a 

decreased duration

, even with as little as 

13 min/day of training. The exception was that long-
term (~2hr) endurance was not maintained in the 
shortest duration (13 min/day) group, however short 
term (~5 min) endurance was maintained. 

(Hickson et al, 1981, 1982, 1985)

Intensity Most Important Factor

•

Little maintenance of physiologic adaptations with 
even the 1/3 

reduction in training intensity

.  

–

Despite training 6 days/week for 40 min/day VO

2

max, long-

term endurance, and left ventricular mass were not 
maintained with 1/3 reduction in training work rate. 

–

Alarmingly, all training-induced increases in left ventricular 
mass were completely lost when work rate was reduced by 
1/3. 

–

Training HR from 180 to 150 beats/min.

•

To minimize crew time spent on exercise, exercise 
frequency and duration may be reduced but intensity 
must be as high as reasonably possible.

(Hickson et al, 1981, 1982, 1985)

ISS Aerobic Exercise

•

Currently 30-40 min at 70-85% HRmax
on CEVIS or TVIS.

•

Research overwhelmingly shows higher 
intensity is required for physiologic 
adaptations.

•

Interval work suggested.

Aerobic Intervals

•

20-30 second “all out sprints”

–

Shortest well documented training

–

Elicits CV adaptations primarily at 
peripheral sites

•

Increased muscle oxidative enzymes  and 
mitochondrial biogenesis

–

Very short exercise durations

•

8 sets of 20 sec sprint with 10 sec recovery 
takes 4 min + warmup/cool down.

Burgomaster et al., 2008; Gibala & McGee, 2008; Gibala et al., 2008; Tabata et al., 1996

Medium Intervals

•

2-3 minute intervals

–

Bedrest evidence of maintenance of VO

2

max 

(Lee et al., 2008)

–

2 min interval sometimes used on ISS

•

7 minute warm up at 40% of VO

2

max, followed 

by 5x2 minute stages at 60,70,80,90,80% 
VO2max, 5 min cool down 

(Greenleaf et al., 1989).

•

Well tolerated by crew, anectdotal evidence

Long Intervals

•

4 minutes

–

Large number of ground based training studies 
support 4 min intervals over continuous exercise.

–

Best results when intensity is maintained ~90%

–

4x4 min at 90-95% HRmax particularly good for 
increasing stroke volume 

(Helgerud et al 2007).

–

Elderly post MI heart failure patients show 
increases in VO

2

max & perform exercise at home. 

(Wisloff et al, 2007)

Bone 

•

Bedrest studies - exercise interventions 
effective in reducing some, but not all bone 
loss.

–

Linearly periodized resistance exercise program and increased 
bone mineral density (BMD) in the lumbar spine, preserved bone in 
the heel, femoral neck and total hip, but was effective at the 
trochanter in only those subjects with dynamic loading of the hip on 
single heel raises 

(Shackelford et al., 2004).

–

Fixed traditional training program of leg and calf press using a 

flywheel device combined with low body negative pressure (LBNP) 
treadmill exercise alleviated about half of the bone loss in the
trochanter and total hip 

(Smith et al., 2008).

ISS Exercise and Bone

•

Evidence from missions on ISS (expeditions 1-15; n=19) show 
modest correlations (r=0.4-0.55) with bone mineral density and 
time/intensity of exercise. 

•

Trochanter, lumbar spine, and whole body BMD correlated with 
total aerobic exercise time above 70% HRmax.

•

Trochanter and pelvis BMD correlated with total number of total 
exercise sessions.  

•

Femoral neck and lumbar spine BMD correlated with total 
treadmill exercise time. 

•

Pelvis BMD correlated with IRED deadlift load used during 
training, but other IRED correlations were much lower 
(unpublished internal data).

Bone

•

High magnitude 

(Rubin & Lanyon, 1985)

and rate of 

dynamic (not static) strain 

(Hsieh & Turner, 2001).

– Periodized resistance training program where the 

magnitude and rate of strain is regularly altered

.

•

Diverse strain distributions as bone 
adaptations are well documented to be site 
specific in humans as evidenced by both 

in 

vitro

(Bass et al., 2002)

and 

in vivo

investigations 

(Maple et 

al, 1997; Winters-Stone & Snow, 2006).

– Periodized resistance training whereby the 

resistance exercises are varied to yield diverse 
strain distributions.

Bone

•

Only a few repetitions are required 

(Rubin & Lanyon, 1984).

–

36 cycles of loading per day is as effective as 360 
cycles/day when the strain rate is high.

–

Minimal number of repetitions is dependent on the 
load, with higher loads requiring fewer repetitions 

(Cullen et al, 2001)

– 2 shorter higher intensity exercise sessions in one 

day as opposed to one longer session

Bone

•

Multiple daily exercise sessions optimize 
bone growth 

(Robling et al., 2000).

–

Resting ~4 h between bouts nearly doubled bone 
formation responses in rodents 

(Robling et al. 2001).

–

Significant correlations among trochanter and 

pelvis BMD and total number of exercise sessions 
on ISS.

–

Femoral neck and lumbar spine BMD correlated 
with total treadmill exercise time on an ISS.

– 2 exercise sessions in one day as opposed to one 

longer session; maximize intensity

Bone

•

Longer rest intervals between sessions 
and sets

is beneficial.  

–

Bone quickly sensitizes to the mechanical loading 
stimulus, allowing rest periods between sessions 
allows for restoration of the mechanosensitivity. 

–

8 hours of recovery is required to regain full 
mechanosensitivity of bone & 14 seconds is the 
optimal time between loading cycles within an 
exercise session in rodents. 

(Robling et al., 2001).

– This supports the notion of having 2 exercise 

sessions in one day separated by several hours 
as opposed to one longer session

Muscle

•

>25 bedrest and ULLS studies evaluating 
exercise as a countermeasure for muscle 
size/strength

•

Variety of exercises used

–

LBNP treadmill

–

Flywheel

–

Traditional weights

•

All exercise programs that were effective in 
maintaining muscle size/strength used 
maximal or nearly maximal contractions

. 

Examples of Effective Countermeasures

•

Traditional weights 

–

21 day ULLS KE and PF

–

10 reps at 40%, 2 MVIC, 10 reps at 80%, a 
final set of as many reps as possible of 
isotonic exercise at 80%. 

–

Every 3 days

–

Total exercise time (including rest) was 6.5 
min

–

KE and PF CSA and MVC were maintained

Schulze et al., 2002

Countermeasures

•

Traditional weights

–

14 Days Bedrest

–

5 sets of leg press every other day at 8 RM

–

1RM & CSA maintained, MVIC not

Bamman et al., 1998

Countermeasures

•

Inertial flywheel

•

60 Day bedrest exercise for squat & calf 
press every 3 days beginning on day 2

•

LBNP treadmill

•

Effective to maintain VL size and 
strength but not SOL (28% vs 8% loss)

(Trappe et al., 2007, 2007, 2008)

•

Use of maximal or nearly maximal 
contractions!

•

Calf and thigh require different stimuli

Common To Effective Countermeasures

Countermeasures

•

So…how do you design exercise 
programs for spaceflight?

•

If it works in bedrest does it work with 
spaceflight?

Flight Countermeasures Improving

•

NASA/MIR – elastic expanders 

–

16 crew, ~140 days, 10%, 13% loss in 
muscle 

mass

in QF and calf

•

ISS – IRED

–

18 crew, ~180 days 11%, 18% loss QF, 
calf 

strength

QuickTime™ and a

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are needed to see this picture.

Bedrest vs. Spaceflight

•

Length of study

–

Few bedrest studies as long as 90 days

–

ISS flights 180 days

•

Presence of gravity in bedrest

–

Movements in bed still against gravity

–

Lumbar spine

–

Other stressors in flight, calm & safe in 
bedrest

Exercise Equipment on ISS

•

Advanced Resistance Exercise Device 
(ARED)

ARED

•

Greater loads – 600 lbs

–

Pneumatic cylinders

•

Constant load

•

Ecc-Con ratio ~90%

–

Flywheels

•

Simulated inertia

•

29 different exercises

•

Instrumented 

ISS Exercise Equipment

•

TEVIS 

•

CEVIS

•

T2 soon

Resistance Exercises – Weekly Schedule

Heavy

Light

Moderate

12

Moderate

Heavy

Light

11

Light

Moderate

Heavy

10

Heavy

Light

Moderate

9

Moderate

Heavy

Light

8

Light

Moderate

Heavy

7

Heavy

Light

Moderate

6

Moderate

Heavy

Light

5

Light

Moderate

Heavy

4

Heavy

Light

Moderate

3

Light

Light

Light

2

Light

Light

Light

1

Week

Front Squat, Bent-over 
Row, Single Leg  Knee 
Extension, Bench Press, 
Heel Raise

Dead Lift, Shoulder Press, 
Single Leg Squat, Bent-over 
Row, Single Leg Heel Raise

Squat, Bench Press, 
Romanian Dead Lift, 
Upright Row, Heel Raise

Day 3

Day 2

Day 1

Resistance Exercise Session Details

60

50

35

Total Time (min)

180

150

90

Rest (sec)

3

6

10

Reps

4

4

3

Sets

Heavy

Moderate

Light

Weeks 7-12

40

40

35

Total Time (min)

120

120

90

Rest (sec)

5

8

12

Reps

3

3

3

Sets

Heavy

Moderate

Light

Weeks 1-6

Aerobic Interval Exercises

•

Short Sprint

-

10 minute warm up at 50% of HRmax, followed by 

7-8 sets of maximal exercise for 30 seconds, followed by 15 
seconds rest.  Increase load after 9 sets

•

2 minute

-

5 minute warm up at 50% VO

2

max, followed by  6x2 

minute stages at 70, 80, 90, 100, 90%, 80% VO

2

max. The first 5 

stages are separated by 2 minute active rest stages at 50% VO

2

max. The final stage is a 5 min active rest at 40% VO

2

max

.

•

4 minute

-

5 minute warm up at ~50% HRmax, followed by 

intervals of exercise at 90% HRmax. The exercise intervals will be 
4x4 min bouts, with 3 min active rest periods. 

Integration of Resistance and Aerobic

30 

min

30 

min

30 

min

Aerobic Continuous

35 

min

15 

min

32 

min

Aerobic Interval

35-60 

min

35-60 

min

35-60 

min

Resistance

Day 

7

Day 

6

Day 

5

Day 

4

Day

3

Day 

2

Day 

1

Note:  Time savings up to 3 hours/week compared to current exercise time

At least 4 hrs, preferably 8 hrs separating exercise sessions 

Pre- and Post-Flight Measurements

•

Muscle CSA

–

Pre/Post-flight MRI – Availability at landing?

–

Pre/In/Post-flight Ultrasound – In-flight?

•

Muscle Function Test from FTT

–

Power, endurance, CAR, steadiness

•

Single fiber size, contractile function, type

•

Aerobic & glycolytic enzymes

–

Citrate synthase & PFK

Pre- and Post-Flight Measurements

•

Cardiovascular

–

Pre/In/Post-flight VO

2

max

–

Ventilatory threshold pre/post-flight using standard ramp cycle 
protocol

•

50 Watts for 3 min then increased by 25 Watts/min thereafter

–

HR response to submax load pre/in/post

–

US for cardiac contractility

•

Bone

–

QCT as a standard medical test. Structural parameters can be 
estimated from 2-d DXA scans by hip structure analysis in the 
absence of QCT scans.

–

Request data sharing with with MedB8.1/Clinical Nutritional 
Assessment and the SMO 016E/Nutritional Status Assessment for 
bone markers.

Pre-Post-Flight Test Schedule

60 min

Bone

Postflight <R+30

60, 60 min

Isokinetic knee, ankle, back, 

functional fit = 

Muscle

Postflight R+30

40, 60 min

Cycle 

=VO

2

max

Postflight R+29

60 min

Isokinetic knee, ankle, back

Postflight R+14

60 min

Cycle

=VO

2

max

Postflight R+10

60, 40, 30 min

MRI, US

Postflight R+6

60,60 min

Isokinetic knee, ankle, 

functional fit =

Muscle

Postflight R+5

50, 60 min

Muscle, VO

2

max

Postflight R+1

30 min, 60 min

MRI or US, Biopsy

Postflight R+0 

60, 50, 30, 60 

min

MRI, Muscle, US, VO

2

max

Preflight  L-10

60, 50, 30, 60 

min

MRI, US , 

functional 

fit=

Muscle, 

Cycle

=VO

2

max

Preflight  L-45-50

60 min

Biopsy

Preflight L-50-55

60 min

Isokinetic knee, ankle, back

Preflight L-60-90

75 min

Isokinetic knee, ankle, back

Preflight L-180

60 min

Bone

Preflight  L<365

Time Required

Test

Time

•

In-flight Data

Muscle Size??

Vastus lateralis
via ultrasound

VO

2

max

Every 30 days

Muscle Strength

5 RM weeks 1-7

3RM after week 7

Pre-flight testing = 11 
hrs

Post-flight testing= 
14 hrs

Summary

•

New ISS exercise hardware should 
allow for exercise at intensities high 
enough to be expected to elicit adaptive 
responses and provide quantitative 
information about loading.

•

New ExRx should incorporate higher 
intensity exercises and seek to optimize 
intensity, duration and frequency to 
yield an efficient ExRx.