“We now have humans who live apart from Earth for prolonged periods; as crews on the Space Station. A key question that remains unanswered is whether humans can travel the long distances required for the exploration of other planets, perform tasks necessary to carry out surface explorations and return to Earth with good health and physical capacity. Developing effective exercise protocols and the equipment to carry them out remains a critical challenge for today’s researchers and space travellers.” Bill Shepherd – American Astronaut (retired)
Exposure to an environment of microgravity; such as the environment in space, will cause measurable immunological, cardiovascular and musculoskeletal changes in humans, as well as having profound effects on how the body ingests and processes vital nutrients. The environmental stresses faced by astronaut’s means some serious dedication to exercise and diet; before, during and after space travel. International Space Station (ISS) crew members train for years to develop the stamina, muscle mass and cardio capacity necessary to withstand the stresses of space travel and it may only take a few days for all this hard work to come undone once out in space. Reports show that after 2 weeks in microgravity there is a significant loss to pre-flight aerobic capacity, bone health and strength.
Training an astronaut for a spacewalk in zero gravity is not all that different from preparing an athlete for competition. This is the job of astronaut physical trainer Beth Shepherd, who is responsible for designing and monitoring individual training programmes. Pre-programme training consists of lots of upper body exercises; specifically squats, deadlifts and heel raises, these are known as ‘The Big 3’ and are important for strengthening the bones in the hips, upper leg and heels. These areas are at particular risk of deterioration during space flight; as an accelerated loss of bone density (through resorption) in space starts to occur after just 10 days! In fact, in zero gravity your muscle mass and bone density will drop at a rate of about 1-2% a month and as if that wasn’t problematic enough; your heart muscle atrophies (tissue wastes away), your resting heart rate increases, body fluid shifts, appetite becomes supressed and your body’s nutritional profile becomes drastically altered. Reports by NASA show they are seeing significant bone loss in the hip, pelvis and head of the femur of astronauts returning to Earth, as well as a loss of up to 30% of muscle function and 15% of muscle mass, during an average 6 month assignment.
Pre-programme training will also concentrate on strengthening the shoulders, forearms, wrists and hands; as space walks require forearm, grip strength and a certain amount of upper body strength. On Earth you tend to use the larger muscle groups (legs and back) to move around, but in a microgravity environment these muscle groups become pretty much redundant and it’s the smaller muscle groups (arms, hands and shoulders) that tend to do all the work. Space walks can last for up to 6 hours and involve repetitive motions and any repair/building work on the ISS requires maximum reach, flexibility and strength; so as well as good hand, shoulder and forearm strength, astronauts must also have a sound cardio capacity.
Once out in space astronauts exercise 6 days a week for 2 ½ hours a day; this in-flight programme consists of resistance training in the form of leg exercises (every day), upper body exercises every other day and cardio 5 hours a week. This level of exercise is vital in aiding the maintenance of muscle mass, bone density and cardio capacity. Research shows that in order to protect the muscles from atrophy and loss of function; then high intensity interval training should be performed in short bursts of high intensity resistance training at 80% of the muscles max capacity for 15 mins twice a day. This has been shown to be more effective than long periods of low intensity aerobic exercise. Intense weight bearing exercise may also protect against bone loss.
Obviously weight training in space is virtually impossible as it is a weightless environment; to combat this NASA developed the IRED or Interim Resistive Exercise Device. The IRED is made up of elastic coils packed into metal cylinders that are bolted to the floor about 2 feet apart. Connected to the cylinders; via steel cables, are enormous shoulder pads. The astronauts strap themselves in and then push upwards from a squat position; thus pulling the cables to stretch the elastic bands, which are coiled up inside the cylinders. This achieves a lower body workout in a weightless environment; which will help in combatting muscle wastage in these areas, but unfortunately does very little, if anything for bone density. Studies show that in order to protect against loss of bone density the astronauts must perform exercises that deformed the bone cells; this slows bone mineral resorption (a natural process in the body that weakens bones). You should bear in mind that here on Earth men start to find it hard to add bone mass around age 30.
There are 3 key factors that must be observed when performing these exercises:
- Astronauts should use heavy weights; at least 80% of their 1 rep maximum. Heavy lifting rather than static loading (as during a jog) is the only way to deform the bone cells enough to grow cortical bone. To achieve this effect on Earth you should perform exercises such as squats, bench press and deadlifts; at 80-85% of your 1 rep max. This is proven to be the most effective way to stop bone and muscle deterioration.
- Strength exercises should be performed slowly, therefore increasing eccentric force; this is important for maintaining bone density. Studies show that men on a steady diet of exercises with free weights, using eccentric forces over a period of 16 weeks, had improved bone mineral density.
- Drop the number of reps and keep the intensity high. A study in 2010 by Scott Trappe; the director of the human lab at Ball State University Indiana USA, concluded that intense movements like sprinting, jumping and throwing along with heavy weights and low reps (6-8), resulted in more muscle mass. Muscle mass is a key element in protecting bones and thus keeping them from ageing too quickly. What you should take from this; training hard, a bit less frequently with slow negatives, heavy weights and less reps, will result in more muscle mass and the effective maintenance of bone density.
*Nasa have since replaced the IRED with the ARED (Advanced Resistive Exercise Device), which as its name suggests is an 'updated' version of the IRED.
Other exercises that should be used in conjunction with heavy weights in order to help turn back the ageing process in muscle and bone are: Medicine ball chest throw, lateral cone hops, sprints, medicine ball overhead throw, plyometric push-ups and box jumps.
The IRED is not the only piece of exercise equipment astronauts have at their disposal. The Cycle Ergometer simulates a bike workout; allowing a dynamic leg exercise whilst also stimulating a cardiovascular response. Unfortunately the Cycle Ergometer has proven ineffectual in preventing musculoskeletal deterioration due to the low stress involved in pedalling. There is also a treadmill aboard the ISS, known as the Treadmill Vibration Isolation System (TVIS); which is allowed to float, but is secured by a flexible cable to stop it from drifting away. The astronauts are strapped on to the treadmill, which allows running and walking with forces equivalent to gravity on Earth; it is designed to load the body in order to prevent musculoskeletal atrophy of the weight bearing muscles and bones. The treadmill also prevents deterioration of the cardiovascular system; as run and walk training in 1g will reduce resting and submaximal heart rates, as well as increasing stroke volume.
Since exposure to microgravity causes a decrease in the mass of the heart, decreased cardiovascular fitness, decreased maximal oxygen consumption, increased lactate accumulations for submaximal work, body fluid shifts and an increase in resting heart rate, then exercise is paramount to the maintenance of cardiovascular health and ultimately to the survival of the astronaut.
The shift of fluid from the lower body to the Thoraco Cephalic regions (upper regions) is the primary reason for cardiac deconditioning of the body. The heart is allowed to move fluids around the body freely and therefore muscular activity of the heart is decreased; thus the mass of the heart decreases, resulting in a decrease in stroke volume. This forces the cardiovascular system to compensate by increasing the heart rate during rest and submaximal exercise.
A reduction in the load on the muscles in a microgravity environment leads to lower oxygen requirements associated with normal activity; this coupled with fluid shifts causing plasma to be lost throughout the body, ultimately meaning a reduction of red blood cells. This leaves the muscles oxygen deficient during increased workloads and leads to a greater accumulation of blood lactate. The end result of weightlessness is a decrease in cardiovascular fitness and a reduction in performance.
After 6 months aboard the ISS; astronauts returning to Earth can look forward to 45 days of physical rehabilitation and it often takes 3 times the actual space journey to fully recover from its effects! A study of 13 space station residents found that 3 had lost as much as 30% of their bone strength; making them as frail as an older women on Earth who was suffering from Osteoporosis!