Space Shuttle Reduced muscle mass, strength and performance in space

figure 6-5. first-generation or original space shuttle passive treadmill. reference.

the collective specific aim of dso 477 , dso 617 evaluate functional changes in concentric , eccentric strength (peak torque) , endurance (fatigue index) of trunk, arms, , legs of crewmembers before , after flight. lido® dynamometer located @ johnson space center , @ both prime , contingency landing sites used evaluate concentric , eccentric contractions before , after flight.

test subjects in study exercised during flight various durations, intensities , numbers of days on original shuttle treadmill (figure 6-5) (as opposed edo treadmill, flew on later shuttle missions , bases iss treadmill) part of separate in-flight investigations. exercise protocols included continuous , interval training, prescriptions varying 60% 85% of preflight vo2-max estimated heart rate (hr) subjects had difficulty in achieving or maintaining target hr during flight. brake (figure 6-5). harness , bungee/tether system used simulate body weight providing forces equivalent approximate 1-g body mass. subjects on non-motorized treadmill required walk , run @ positive percentage grade overcome mechanical friction. study participants familiarized lido® test protocol , procedures 30 days before launch (l-30), after 6 test sessions conducted. 3 sessions completed before launch (l-21, l-14 , l-8 days) , 3 after landing (r+0, r+2 , r+7 r+10 days).

the muscle groups tested shown in table 6-1. torque , work data extracted force-position curves. peak-torque, total work, , fatigue index measured in 3 preflight test sessions compared; when no differences found between sessions, values 3 preflight sessions averaged , average used compare preflight values on landing day , during postflight period.

skeletal-muscle strength defined peak torque generated throughout range of motion 3 consecutive voluntary contractions flexion , extension. eccentric contractions actions of muscle in force generated while muscle lengthening, opposed concentric actions in muscle shortening (contracting) while generating force. skeletal-muscle endurance defined total work generated during 25 repetitions of concentric knee exercise, determined area under torque curve complete exercise set. work compared between first 8 , last 8 repetitions. endurance parameters measured during concentric knee flexion , extension activity only. on r+0, significant decreases in concentric , eccentric strength shown in , abdomen when compared preflight means (table 6-1).

concentric extension , eccentric dorsiflexion remained less preflight values on r+7. recovery (an increase in peak torque r+0 r+7) demonstrated eccentric abdomen , concentric , eccentric extensors.

however, data depicted in table 6-1 may misleading because in cases there tremendous differences in strength between crewmembers exercised during flight versus did not. example, crewmembers exercised during flight gained in isokinetically measured strength in ankle extensor/flexor muscles (anterior versus posterior calf muscles, m. tibialis anterior versus gastrocnemius/soleus complex) compared crewmembers did not exercise , showed decrease in isokinetically measured strength in these muscles (figure 6-6).

figure 6-6. percent change in isokinetic strength in ankle extensor , flexor muscles crewmembers exercised during flight versus did not. †preflight < r+0 (p < 0.05). reference.

with respect endurance, majority of decrease in total quadriceps work occurred on r+0. reflects significant loss in first third of exercise bout (-11%). declines in peak torque @ faster endurance test velocities consistent changes seen @ slower angular velocity used during strength tests. torque quadriceps @ 75° per second 15% less preflight values hamstrings 12% less preflight mean @ 60° per second. endurance data showed little difference between preflight , r+7 tests, suggesting crewmembers had returned baseline 1 week after landing.

additionally, subjects did exercise during flight compared did not had greater (p < 0.05) losses within 5 hours of landing in concentric strength of back, concentric , eccentric strength of quadriceps (30° per second), , eccentric strength of hamstrings, relative respective preflight values (data not shown here). according greenisen et al., non-exercisers had less concentric strength of quadriceps @ 75° per second , lower total work extension, work first-third flexion, , work last-third extension, after landing, before flight. conclusions reached investigators data indicate muscles less able maintain endurance , resist fatigue after spaceflight, , exercise may avert decrements in these aspects of endurance.

conversely, crewmembers exercised during flight had greater losses in trunk muscles strength measured @ landing did non-exercising group (figure 6-7). however, preflight strength in trunk flexion , extension substantially greater in exercising group in non-exercising group. apparently treadmill exercise did not prevent decrements in trunk strength after 9 11 days of spaceflight, , investigators proffered explanation preservation of muscle function may limited muscles used part of exercise regimen.

figure 6-7. percent change in isokinetic strength in trunk muscles in crewmembers exercised during flight versus did not. †pre > r+0 (p < 0.05). reference.

the specific aim of dso 475, direct assessment of muscle atrophy before , after short spaceflight define morphologic , biochemical effects of spaceflight on skeletal fibers. obtain myofiber biomechanical , morphological data space shuttle crewmembers, biopsies conducted once before flight (l - > 21 days) , again on landing day (r+0). subjects 8 crewmembers, 3 5-day mission , 5 11-day mission. biopsies of mid-portion of m. vastus lateralis obtained means of 6-mm biopsy needle suction assist. one-tailed paired t-test used identify significant differences (p < 0.05) between mean values of fiber cross-sectional area (csa), fiber distribution, , number of capillaries of crewmembers before flight , mean values crewmembers after flight.

according report, csa of slow-twitch (type i) fibers in postflight biopsies 15% less in preflight biopsies; csa of fast-twitch (type ii) fibers 22% less after flight before (figure 6-8). mean values did not reflect considerable variation seen in biopsies 8 astronauts participated. @ least of variation resulted differences in types , quantities of preflight , in-flight countermeasures (exercise or lbnp) used different crewmembers. relative proportions of type , type ii fibers different before , after 11 day mission: fiber distribution seemed follow same trend after 5 day mission (more type ii , fewer type fibers after before), sample size small reach statistical significance. number of capillaries per fiber reduced after 11 days of spaceflight.

figure 6-8. percent change in csa of type (slow twitch) , type ii (fast twitch) myofibers in postflight versus preflight muscle biopsies 8 crewmembers. reference.

however, since mean fiber size reduced, number of capillaries per unit of csa of skeletal muscle tissue remained same. atrophy of both major myofiber types, atrophy of type ii > type i, different more selective type myofiber atrophy observed in unloaded sprague-dawley , wistar rat muscle representing uncommon case in difference exist between responses of human , murine skeletal muscle.

the purpose of dso 606, quantifying skeletal muscle size magnetic resonance imaging (mri), non-invasively quantify changes in size, water, , lipid composition in antigravity (leg) muscles after spaceflight. experiment first attempt measure limb volumes before , after flight since less sophisticated methods of measuring limb girths during apollo , skylab programs used. subjects included total of 8 space shuttle crewmembers, 5 7-day flight , 3 9-day flight. subjects completed 1 preflight , 2 postflight tests on either l-30 or l-16 , on r+2 , r+7. testing involved obtaining mri scan of leg (soleus , gastrocnemius) @ university of texas - houston health science center, hermann hospital. multi-slice axial images of leg obtained identify , locate various muscle groups. changes in water , lipid content measured, in addition csa, distinguish changes in fluid versus tissue volumes. multiple slices measured computerized planimetry.

csa , volume of total leg compartment, soleus, , gastrocnemius evaluated assess degree of skeletal muscle atrophy. volumes of 3 compartments smaller (p < 0.05) after both 7 , 9 day shuttle flights before flight. volume decreased 5.8% in soleus, 4.0% in gastrocnemius, , 4.3% in total compartment. these losses stated represent true level of skeletal muscle tissue atrophy , not changes associated fluid shifts. no recovery apparent 7 days after landing (data not shown). interesting finding , indicates losses not due fluid shifts, delay in recovery after these rather short flights contrary observed , documented during skylab program of flights longer in duration, albeit less sophisticated methods during skylab.

the space shuttle program and, in particular, edomp has provided great deal of knowledge effects of spaceflight on human physiology , on alterations in skeletal muscle mass, strength, , function. once again, losses of skeletal muscle mass, strength, , endurance documented, in cases in spite of exercise countermeasures. findings encouraging, particularly indications in-flight exercise have positive effect in countering losses in muscle strength @ least in legs (see table 6-1 , figure 6-6), predicted results of 84-day skylab 4 mission when multiple modesof exercise used including unique treadmill device (see figure 6-4). unusual treadmill provided loads of sufficient magnitude legs in fashion approaching resistance exercise. however, data provided mri volume studies indicate not crewmembers, despite utilization of various exercise countermeasures, escape loss in muscle mass has been documented during of history of u.s. human spaceflight since project mercury. this, additional research needed continue development of countermeasures , equipment provide successful solution human space travelers.