Engineering topics

Watenpaugh, D. E.

Publications and source records attributed to Watenpaugh, D. E..

At least 37 records · Page 2

NASA NTRS1996

Cardiovascular adaptation to spaceflight

This article reviews recent flight and ground-based studies of cardiovascular adaptation to spaceflight. Prominent features of microgravity exposure include loss of gravitational pressures, relatively low venous pressures, headward fluid shifts, plasma volume loss, and postflight orthostatic intolerance and reduced exercise capacity. Many of these short-term responses to microgravity extend themselves during long-duration microgravity exposure and may be explained by altered pressures (blood and tissue) and fluid balance in local tissues nourished by the cardiovascular system. In this regard, it is particularly noteworthy that tissues of the lower body (e.g., foot) are well adapted to local hypertension on Earth, whereas tissues of the upper body (e.g., head) are not as well adapted to increase in local blood pressure. For these and other reasons, countermeasures for long-duration flight should include reestablishment of higher, Earth-like blood pressures in the lower body.

Review, Tutorial↗

NASA NTRS1996

Cerebrovascular Responses During Lower Body Negative Pressure-Induced Presyncope

Reduced orthostatic tolerance is commonly observed after space flight, occasionally causing presyncopal conditions. Although the cerebrovascular system may play an important role in presyncope, there have been few reports concerning cerebral hemodynamics during presyncope. The purpose of this study was to investigate cerebrovascular responses during presyncope induced by lower body negative pressure (LBNP). Seven healthy male volunteers were exposed to LBNP in steps of -10 mmHg every 3 min until presyncopal symptoms were detected. Blood pressure (BP) and heart rate (HR) were measured with a finger cuff. Cerebral tissue oxy- and deoxy- hemoglobin (Hb) concentrations were estimated using near infrared spectroscopy (NIRS). Cerebral blood flow (CBF) velocity at the middle cerebral artery was measured with Transcranial Doppler Sonography (TCD). We focused on the data during the 2 min before endpoint. BP marked a gradual decrease (91 to 86 mmHg from 2 min to 30 sec before endpoint), which was accelerated along with HR decrease during the final 30 sec (86 to 71 mmHg). Cerebral oxy-Hb concentration decreases as presyncope is approached while total-Hb concentration remains fairly constant. TCD reveals a decrease in the CBF velocity. The TCD and NIRS results suggest that CBF decreases along with the BP decrease. Cerebrovascular responses during presyncope are closely related to cardiovascular responses.

Kuriyama, Kana↗

NASA NTRS1996

Daily Supine LBNP Treadmill Exercise Maintains Upright Exercise Capacity During 14 Days of Bed Rest

Exposure to microgravity or bed rest reduces upright exercise capacity. Exercise modes, durations, and intensities which will effectively and efficiently counteract such deconditioning are presently unresolved. We that daily supine treadmill interval training with lower body negative pressure (LBNP) would prevent reduction in upright exercise capacity during 14 days of 6 deg. head-down bed rest (BR). Eight healthy male subjects underwent two 14 day BR protocols separated by 3 months. In a crossover design, subjects either remained at strict BR or performed 40 min of daily exercise consisting of supine walking and running at intensities varying from 40-80% of pre-BR upright peak oxygen uptake (VO2). LBNP during supine exercise was used to provide 1.0 to 1.2 times body weight of footward force. An incremental upright treadmill test to measure submaximal and peak exercise responses was given pre- and post-BR. In the non-exercise condition, peak VO2 and time to exhaustion were reduced 16 +/- 4% and 10 +/- 1% (p less than 0.05), respectively, from pre-BR. With LBNP exercise these variables were not significantly different (NS) from pre-BR. During submaximal treadmill speeds after BR, heart rate was higher (11 +/- 11 bpm, p less than 0.05) and respiratory exchange ratio was elevated (p less than 0.05) in the no exercise condition. Both were maintained at pre-BR levels in the LBNP exercise condition (NS from pre-BR). Since this supine treadmill interval training with addition of LBNP maintained upright exercise responses and capacity during BR, this countermeasure may also be effective during space flight.

Ertl, Andy C.↗

NASA NTRS1995

Back pain during 6 degrees head-down tilt approximates that during actual microgravity

Astronauts often experience back pain during spaceflight. Retrospectively, Wing et al. (14) found that during spaceflight, 14 of 19 Shuttle crewmembers experienced back pain, which they described as dull (62%), localized to the lower back (50%), and with an intensity of 2 on a 5-point scale. Further, the spine lengthens 4-7 cm in microgravity. Our objective was to compare back pain and spinal lengthening (body height increase) during simulated microgravity (6 degrees head-down tilt, HDT) with the same parameters during actual microgravity. Eight male subjects completed a modified McGill pain questionnaire with intensity graded from zero (no pain) to five (intense and incapacitating pain) each day at 7:00 pm during 2 d pre-HDT control, 16 d HDT, and 1 d post-HDT recovery periods. Also, the subjects' heights were measured each day while supine (control and recovery) and during HDT. Back pain increased from zero (pre-tilt control period) to 2.3 +/- 0.4 at days 1 to 3 of HDT, and was categorized as dull and/or burning pain in subjects' lower backs. Only 2 subjects reported any pain after day 9 of HDT and during recovery. Heights increased 2.1 +/- 0.5 cm by day 3 of HDT and remained at that level until the end of the HDT period. Although spinal lengthening in space is greater than that during HDT, the HDT model approximates the level, type, distribution, and time course of back pain associated with actual microgravity. In the HDT model, pain subsides in intensity when spinal lengthening stops.(ABSTRACT TRUNCATED AT 250 WORDS).

Non-NASA Center↗

NASA NTRS1995

Calf venous compliance measured with head-up tilt equals supine calf compliance

Elevated calf compliance may contribute to orthostatic intolerance following space flight and bed rest. Calf venous compliance is measured conventionally with venous occlusion plethysmography in supine subjects. With this well-established technique, subjects undergo inflation of a pressure cuff around the thigh just above the knee, which increases calf venous pressure. A plethysmograph simultaneously measures calf volume elevation. Compliance equals calf volume elevation per mm Hg thigh occlusion (calf venous) pressure in relaxed legs of the supine subjects. Compliance may also be measured during stepwise head-up tilt (HUT) as calf volume elevation per mm Hg gravitational venous pressure elevation produced by HUT. However, during HUT on a tilt table with a footplate, calf muscles activate to counteract gravity: this is an obvious and natural response to gravitational force. Such muscle activation conceivably could reduce calf compliance, yet relatively little calf muscle activation occurs during HUT and orthostasis (less than 10% of maximal voluntary levels; 4, 8, 10). Also, this activation produces minimal calf volume change (less than 0.3%; 3). Therefore, we hypothesized that calf compliance measured with HUT equals that measured with supine venous occlusion.

Watenpaugh, D. E.↗

NASA NTRS1995

Ultrasound measurement of transcranial distance during head-down tilt

Exposure to microgravity elevates blood pressure and flow in the head, which may increase intracranial volume (ICV) and intracranial pressure (ICP). Rhesus monkeys exposed to simulated microgravity in the form of 6 degree head-down tilt (HDT) experience elevated ICP. With humans, twenty-four hours of 6 degree HDT bed rest increases cerebral blood flow velocity relative to pre-HDT upright posture. Humans exposed to acute 6 degree HDT experiments increased ICP, measured with the tympanic membrane displacement (TMD) technique. Other studies suggest that increased ICP in humans and cats causes measurable cranial bone movement across the sagittal suture. Due to the slightly compliant nature of the cranium, elevation of the ICP will increase ICV and transcranial distance. Currently, several non-invasive approaches to monitor ICP are being investigated. Such techniques include TMD and modal analysis of the skull. TMD may not be reliable over a large range of ICP and neither method is capable of measuring the small changes in pressure. Ultrasound, however, may reliably measure small distance changes that accompany ICP fluctuations. The purpose of our study was to develop and evaluate an ultrasound technique to measure transcranial distance changes during HDT.

Torikoshi, S.↗

NASA NTRS1995

Measurement of Transcranial Distance During Head-Down Tilt Using Ultrasound

Exposure to microgravity probably elevates blood pressure and flow in the head which may increase intracranial volume (ICV) and pressure (ICP). Due to the slightly compliant nature of the cranium, any increase of ICP will increase ICV and transcranial distance. We used a noninvasive ultrasound technique to measure transcranial distance (frontal to occipital) during head-down tilt. Seven subjects (ages 26-53) underwent the following tilt angles: 90 deg. upright, 30 deg., 0 deg., -6 deg., -10 deg., -6 deg., 0 deg., 30 deg., and 90 deg. Each angle was maintained for 1 min. Ultrasound wave frequency was collected continuously and transcranial distance was calculated (Delta(x) = x(Delta)f/f, where x is path length and f is frequency of the wave) for each tilt angle. Frequency decreased from 503.687 kHz (90 deg. upright) to 502.619 kHz (-10 deg.). These frequencies translated to an increased transcranial distance of 0.403 mm. Although our data suggest a significant increase in transcranial distance during head-down tilt, this apparent increase may result, in part, from head-down tilt-induced subcutaneous edema or cutaneous blood volume elevation. In three subjects, when the above protocol was repeated with an ace bandage wrapped around the head to minimize such edema, the increased transcranial distance from 90 deg. to -10 deg. was reduced by 0.174 mm. Further development of the technique to quantify bone-to-bone expansion unconfounded by cutaneous fluid is necessary. Therefore, this ultrasound technique may provide measurements of changes in cranial dimensions during microgravity.

Torikoshi, Shigeyo↗

NASA NTRS1995

Near-Infrared Monitoring of Model Chronic Compartment Syndrome In Exercising Skeletal Muscle

Chronic compartment syndrome (CCS) is characterized by muscle ischemia, usually in the anterior oompartment of the leg, caused by high intramuscular pressure during exercise. Dual-wave near-infrared (NIR) spectroscopy is an optical technique that allows noninvasive tracking of variations in muscle tissue oxygenation (Chance et al., 1988). We hypothesized that with a model CCS, muscle tissue oxygenation will show a greater decline during exercise and a slower recovery post-exercise than under normal conditions.

Hargens, Alan R.↗

NASA NTRS1994

Intramuscular pressures beneath elastic and inelastic leggings

Leg compression devices have been used extensively by patients to combat chronic venous insufficiency and by astronauts to counteract orthostatic intolerance following spaceflight. However, the effects of elastic and inelastic leggings on the calf muscle pump have not been compared. The purpose of this study was to compare in normal subjects the effects of elastic and inelastic compression on leg intramuscular pressure (IMP), an objective index of calf muscle pump function. IMP in soleus and tibialis anterior muscles was measured with transducer-tipped catheters. Surface compression between each legging and the skin was recorded with an air bladder. Subjects were studied under three conditions: (1) control (no legging), (2) elastic legging, and (3) inelastic legging. Pressure data were recorded for each condition during recumbency, sitting, standing, walking, and running. Elastic leggings applied significantly greater surface compression during recumbency (20 +/- 1 mm Hg, mean +/- SE) than inelastic leggings (13 +/- 2 mm Hg). During recumbency, elastic leggings produced significantly higher soleus IMP of 25 +/- 1 mm Hg and tibialis anterior IMP of 28 +/- 1 mm Hg compared to 17 +/- 1 mm Hg and 20 +/- 2 mm Hg, respectively, generated by inelastic leggings and 8 +/- 1 mm Hg and 11 +/- 1 mm Hg, respectively, without leggings. During sitting, walking, and running, however, peak IMPs generated in the muscular compartments by elastic and inelastic leggings were similar. Our results suggest that elastic leg compression applied over a long period in the recumbent posture may impede microcirculation and jeopardize tissue viability.(ABSTRACT TRUNCATED AT 250 WORDS).

Clinical Trial↗

NASA NTRS1994

Supine exercise during lower body negative pressure effectively simulates upright exercise in normal gravity

Exercise within a lower body negative pressure (LBNP) chamber in supine posture was compared with similar exercise against Earth's gravity (without LBNP) in upright posture in nine healthy male volunteers. We measured footward force with a force plate, pressure in soleus and tibialis anterior muscles of the leg with transducer-tipped catheters, calf volume by strain gauge plethysmography, heart rate, and systolic and diastolic blood pressures during two conditions: 1) exercise in supine posture within an LBNP chamber during 100-mmHg LBNP (exercise-LBNP) and 2) exercise in upright posture against Earth's gravity without LBNP (exercise-1 G). Subjects exercised their ankle joints (dorsi- and plantarflexions) for 5 min during exercise-LBNP and for 5 min during exercise-1 G. Mean footward force produced during exercise-LBNP (743 +/- 37 N) was similar to that produced during exercise-1 G (701 +/- 24 N). Peak contraction pressure in the antigravity soleus muscle during exercise-LBNP (115 +/- 10 mmHg) was also similar to that during exercise-1 G (103 +/- 13 mmHg). Calf volume increased significantly by 3.3 +/- 0.5% during exercise-LBNP compared with baseline values. Calf volume did not increase significantly during exercise-1 G. Heart rate was significantly higher during exercise-LBNP (99 +/- 5 beats/min) than during exercise-1 G (81 +/- 3 beats/min). These results indicate that exercise in supine posture within an LBNP chamber can produce similar musculoskeletal stress in the legs and greater systemic cardiovascular stress than exercise in the upright posture against Earth's gravity.

NASA Center ARC↗

NASA NTRS1994

Dynamic Leg Exercise Improves Tolerance to Lower Body Negative Pressure

These results clearly demonstrate that dynamic leg exercise against the footward force produced by LBNP substantially improves tolerance to LBNP, and that even cyclic ankle flexion without load bearing also increases tolerance. This exercise-induced increase of tolerance was actually an underestimate, because subjects who completed the tolerance test while exercising could have continued for longer periods. Exercise probably increases LBNP tolerance by multiple mechanisms. Tolerance was increased in part by skeletal muscle pumping venous blood from the legs. Rosenhamer and Linnarsson and Rosenhamer also deduced this for subjects cycling during centrifugation, although no measurements of leg volume were made in those studies: they found that male subjects cycling at 98 W could endure 3 Gz centrifugation longer than when they remained relaxed during centrifugation. Skeletal muscle pumping helps maintain cardiac filling pressure by opposing gravity-, centrifugation-, or LBNP-induced accumulation of blood and extravascular fluid in the legs.

Watenpaugh, D. E.↗

NASA NTRS1994

Mechanisms of post-flight orthostatic intolerance

Post-flight orthostatic intolerance is a dramatic physiological consequence of human adaptation to microgravity made inappropriate by a sudden return to 1-G. The immediate mechanism is almost always a failure to maintain adequate tissue perfusion, specifically perfusion of the central nervous system, but vestibular dysfunction may occasionally be the primary cause. Orthostatic intolerance is present in a wide range of clinical disorders of the nervous and cardiovascular systems. The intolerance that is produced by spaceflight and 1-G analogs (bed rest, head-down tilt at a moderate angle, water immersion) is different from its clinical counterparts by being only transiently present in subjects who otherwise have normal cardiovascular and regulatory systems. However, the same set of basic pathophysiological elements should be considered in the analysis of any form of orthostatic intolerance.

Non-NASA Center↗

NASA NTRS1994

Head-Down Tilt with Balanced Traction as a Model for Simulating Spinal Acclimation to Microgravity

Astronauts experience total body height increases of 4 to 7 cm in microgravity. Thus, stretching of the spinal cord, nerve roots, and muscular and ligamentous tissues may be responsible for the hyperreflexia, back pain, and muscular atrophy associated with exposure to microgravity. Axial compression of the spine makes 6 deg. head-down tilt (HDT) an unsuitable model for spinal acclimation to microgravity. However, this axial compression may be counteracted by balanced traction consisting of 10% body weight (sin 6 deg. = 0.1) applied to the legs. Six healthy male subjects underwent 3 days each of 60 HDT with balanced traction and horizontal bed rest (HBR), with a 2 week recovery period between treatments. Total body and spine length, lumbar disc height, back pain, erector spinae intramuscular pressure, and ankle joint torque were measured before, during and after each treatment. Total body and spine (processes of L5 - C7) lengths increased significantly more during HDT with balanced traction (22 +/- 8 mm and 25 +/- 8 mm, respectively) than during HBR (16 +/- 4 mm and 14 +/- 9 mm, respectively). Back and leg pain were significantly greater during HDT with balanced traction than during HBR. The distance between the lower end plate of L4 and the upper endplate of S1, as measured by sonography, increased significantly in both treatments to the same degree (2.9 +/- 1.9 mm, HDT with balanced traction; 3.3 +/- 1.5 mm, HBR). Intramuscular pressure of the erector spinae muscles and maximal ankle joint torque were unaltered with both models. While neither model increased height to the magnitude observed in microgravity, HDT with balanced traction may be a better model for simulating the body lengthening and back pain experienced in microgravity.

Ballard, R. E.↗

NASA NTRS1994

Ultrasound as a Noninvasive Method to Assess Changes of Intracranial Volume and Pressure During Simulated Microgravity

Headaches are commonly experienced by astronauts in microgravity and by subjects undergoing head-down tilt (simulated microgravity on Earth). Exposure to microgravity probably elevates blood pressure and flow in the head which may increase intracranial volume (ICV) and pressure (ICP) and in turn cause headache. Due to the slightly compliant nature of the cranial vault and the encasement of brain and its vasculature within this vault, any increase of ICV will increase ICP and slightly distend the cranium. Previous studies document perivascular edema and increased ICP in rhesus monkeys during head-down tilt. Elevated ICP has also been reported in humans during head-down tilt. ICP measurements in healthy humans are rare because of the invasiveness of currently-available measurement techniques. Therefore, we proposed a noninvasive ultrasound technique to assess changes of ICV and JCP. The ultrasound principle is based on compliance of the cranial vault. A 450 kHz ultrasound stimulus is transmitted through the cranium by a transducer every 7.5-10 msec. The ultrasound wave enters the brain tissue, reflects off the opposite side of the cranium and is received by the same transducer. The detected wave is compared for phase quadrature (90 deg.to transmitted wave). Because the electronic circuitry of the device maintains a 90 deg. phase (phi), any alterations in the detected wave caused by an increase of ICV and ICP will be reflected as a change in the wave frequency. Phase shift is directly proportional to path length of the wave, DELTA x, which is expressed as DELTA x = phi lambda/2 pi where lambda is wavelength. Elevated ICV and ICP expand the cranial vault and increase path length of the wave (a measure of intracranial distance). Increased path length equals reduced frequency of the detected wave. Reduced frequency is then related to elevated ICP. This technique has potential uses for ICP studies of astronauts in space and head trauma patients on Earth.

Murthy, G.↗

NASA NTRS1994

Fluid Redistribution and Heart Rate in Humans During Whole-Body Tilting, G(z) Centrifugation, and Lower Body Negative Pressure

Gravity creates blood pressure gradients which redistribute body fluids towards the feet. Positive G(z) centrifugation and lower body negative pressure (LBNP) have been proposed to simulate these and other effects of gravity during long-term existence in microgravity. We hypothesized that the magnitude of upper-to-lower body fluid redistribution would increase according to the following order: short-arm centrifugation (SAC), long-arm centrifugation (LAC), head-up tilt (HUT), and LBNP. To test this hypothesis, we employed strain gauge plethysmography of the neck, thigh and calf during HUT and supine SAC and LAC up to lG(z) at the feet, and during supine LBNP to 100 mm Hg. Supine 100 mm Hg LBNP generates footward force and produces transmural blood pressures in the foot approximately equal to 1 G(z) (90 deg) HUT. Heart rate was measured via cardiotachometry. Control measurements were made while supine. SAC and LAC elicited similar increases in thigh volume at 1 G(z) (2.3 +/- 0.4 and 2.1 +/- 0.1%, respectively; mean +/- se, n greater than or equal to 7). At 100 mm Hg LBNP, thigh volume increased (3.4 +/- 0.3%) significantly more than during l G(z) centrifugation (p less than 0.05). Surprisingly, due to a paradoxical 0.6% reduction of thigh volume between 0.8 and 1.0 G(z) HUT, thigh volume was increased only 0.6 +/- 0.3% at 1 G(z) HUT. The calf demonstrated similar, although less definitive, responses to the various gravitational stimuli. Neck volume tended to decrease less during HUT than during the other stimuli. Heart rate increased similarly during HUT (18 +/- 2 beats/min) and LAC (12 +/- 2 beats/min), and exhibited still greater elevation during LBNP (29 +/- 4 beats/min), yet did not increase during SAC. These results suggest upright posture activates mechanisms that counteract footward fluid redistribution which are not activated during supine applications of simulated gravity. LAC more closely approximated effects of normal gravity (HUT) than LBNP. Therefore, when considering LBNP to simulate gravity, these findings support efforts to reduce the cardiovascular stress imposed by LBNP, while preserving the gravity-like force generated by LBNP.

Watenpaugh, D. E.↗

NASA NTRS1994

Peripheral Microvascular Responses to Whole-Body Tilting, G(z) Centrifugation, and Lower Body Negative Pressure Stresses in Humans

The response of the cutaneous microcirculation to orthostatic stress varies along the length of the body due to the interaction of central controls with regional responses to local blood pressure. We hypothesize that artificial orthostatic stresses such as Gz centrifugation and LBNP differ from whole-body tilting in terms of the distribution of microvascular blood flow. Cutaneous microvascular flows were measured by laser Doppler flowmetry at the neck, thigh, and leg of 15 normal subjects. Volunteers underwent stepwise head-up tilt (HUT) and short- and long-arm centrifugation protocols from supine control (0 Gz) to 0.2, 0.4, 0.6, 0.8, 1.0, 0.8, 0.6, 0.4, 0.2, and 0 Gz at the feet, for 30-s periods with 10-s transitions between levels. The same subjects underwent a corresponding supine LBNP protocol, up to 100 mmHg (in 20 mmHg increments) and back to zero pressure, which produced transmural pressure across blood vessels in the foot approximately equal to the HUT protocol. In general, application of all orthostatic stresses produced significant flow reductions in the lower body (p less than 0.05) and inconsistent changes in the neck. At low levels of each stress (0.4 Gz, 40 mmHg), LBNP generated the greatest relative reduction in flow in the lower body (-66.9+/-5.7%, thigh; -60.6 +/-5.7%, leg, mean +/- SE). HUT caused a less severe flow reduction than LBNP at the thigh and leg (-39.9 +/- 8.1% and -55.9+/-4.8%), while the effects induced by both forms of centrifugation were the least profound. Higher levels of each stress generally resulted in similar responses. These responses exhibit a consistent relationship to hypothesized changes in local microvascular transmural pressure, suggesting that myogenic and veno-arteriolar reflexes play a significant role in determining microvascular perfusion during orthostatic stress.

Breit, G. A.↗

NASA NTRS1994

Noninvasive Intracranial Pressure and Tissue Oxygen Measurements for Space and Earth

The paper discusses the following: Increasing intracranial pressure in humans during simulated microgravity. and near-infrared monitoring of model chronic compartment syndrome in exercising skeletal muscle. Compared to upright-seated posture, 0 deg. supine, 6 deg. HDT, and 15 deg. HDT produced TMD changes of 317 +/- 112, 403 +/- 114, and 474 +/- 112 n1 (means +/- S.E.), respectively. Furthermore, postural transitions from 0 deg. supine to 6 deg. HDT and from 6 deg. to 15 deg. HDT generated significant TMD changes (p less than 0.05). There was no hysteresis when postural transitions to HDT were compared to reciprocal transitions toward upright seated posture. Currently, diagnosis of chronic compartment syndrome (CCS) depends on measurement of intramuscular pressure by invasive catheterization. We hypothesized that this syndrome can be detected noninvasively by near-infrared (NIR) spectroscopy, which tracks variations in muscle hemoglobin/myoglobin oxygen saturation. CCS was simulated in the tibialis anterior muscle of 7 male and 3 female subjects by gradual inflation of a cuff placed around the leg to 40 mmHg during 14 minutes of cyclic isokinetic dorsiflexion exercise. On a separate day, subjects underwent the identical exercise protocol with no external compression. In both cases, tissue oxygenation (T(sub O2) was measured in the tibialis anterior by NIR spectroscopy and normalized to a percentage scale between baseline and a T(sub O2) nadir reached during exercise to ischemic exhaustion. Over the course of exercise, T(sub O2) declined at a rate of 1.4 +/- 0.3% per minute with model CCS, yet did not decrease during control exercise. Post-exercise recovery of T(sub O2) was slower with model CCS (2.5 +/- 0.6 min) than in control (1.3 +/- 0.2 min). These results demonstrate that NIR spectroscopy can detect muscle deoxygenation caused by pathologically elevated intramuscular pressure in exercising skeletal muscle. Consequently, this technique shows promise as a noninvasive diagnostic tool for CCS.

Hargens, A. R.↗

NASA NTRS1993

Intramuscular pressure and electromyography as indexes of force during isokinetic exercise

A direct method for measuring force production of specific muscles during dynamic exercise is presently unavailable. Previous studies indicate that both intramuscular pressure (IMP) and electromyography (EMG) correlate linearly with muscle contraction force during isometric exercise. The objective of this study was to compare IMP and EMG as linear assessors of muscle contraction force during dynamic exercise. IMP and surface EMG activity were recorded during concentric and eccentric isokinetic plantarflexion and dorsiflexion of the ankle joint from the tibialis anterior (TA) and soleus (SOL) muscles of nine male volunteers. Ankle torque was measured using a dynamometer, and IMP was measured via catheterization. IMP exhibited better linear correlation than EMG with ankle joint torque during concentric contractions of the SOL and the TA, as well as during eccentric contractions. IMP provides a better index of muscle contraction force than EMG during concentric and eccentric exercise through the entire range of torque. IMP reflects intrinsic mechanical properties of individual muscles, such as length-tension relationships, which EMG is unable to assess.

Aratow, M.↗