Weeks Of Bed Rest Research Articles

Health Culture in the Heartland, 1880-1980: An Oral History

Lucinda McCray Beier, Professor of History at Illinois State University, brings a wealth of oral history experience to her latest book, Health Culture in the Heartland, 1880–1980. The heartland in this instance is McLean County in north central Illinois, 120 miles southwest of Chicago. Beier's sources include 15 medical practitioners and 26 county residents from varied socioeconomic and ethnic backgrounds, born between 1894 and 1966. Beier's oral histories illustrate dramatic changes in the health culture of McLean County, as its two population centres of Bloomington and Normal grew. The oral histories reveal how urbanisation, as well as scientific and technological advances, affected the development of the county's hospitals, nursing schools, doctors' practices and public health initiatives. Beier also makes good use of medical history literature to show how events in McLean County reflected, or were influenced by, changes occurring elsewhere in the USA. Beier notes that the diseases McLean County residents most feared, and most often died from, were very different at the beginning of the twentieth century than at its end. During a brief span of one or two generations, the management of birth, illness, injury and death moved from homes to medical institutions, and from the responsibility of mainly female lay caregivers to that of formally qualified experts. In this context, Beier examines how residents felt about their experiences with health, illness and medical care, and how their expectations about these matters changed over time. Many McLean County residents recalled suffering from a variety of communicable diseases that were prevalent before immunisations. Nonetheless, they tended to regard their childhoods as healthy. Some remembered weeks of bed-rest when they were ill with infections, or being bedridden for months or years in tuberculosis sanitoria, before the days of antibiotics. One woman recalled family friends, a brother and a sister who had tuberculosis during the 1930s. The young man presumably recovered at the McLean County Tuberculosis Center, but upon discharge ‘did not follow his doctor's orders’ and died. His sister was bedridden at the sanitorium for ‘two or three years’ while each of her lungs were collapsed in turn, ‘to let them rest’, and ‘had to learn to walk all over again’ when she was discharged (p. 145). These kinds of first-person accounts, predominantly from a rural perspective, are what sets Beier's book apart from others covering the same period of medical history.

Effect of prolonged bed rest on the anterior hip muscles

Prolonged bed rest and inactivity is known to cause muscular atrophy with previous research indicating that muscles involved in joint stabilisation are more susceptible. The anterior hip muscles are important for hip joint function and stability but little is known about the effects of prolonged inactivity on their function. This study investigated the effect of prolonged bed rest on the size of the anterior hip muscles and their pattern of recovery. The effect of resistive vibration exercise (RVE) as a countermeasure to muscle atrophy was also investigated. 12 male participants, randomly assigned to either a control or an exercise group, underwent 8 weeks of bed rest with 6 months follow-up. Changes in muscle cross-sectional area (CSA) of the iliacus, psoas, iliopsoas, sartorius and rectus femoris muscles were measured by magnetic resonance imaging at regular intervals during bed rest and recovery phases. CSAs of iliopsoas and sartorius decreased at the hip joint ( p < 0.05) during bed rest but iliacus, psoas, and rectus femoris CSAs were unchanged ( p > 0.05). No significant difference was found between the two groups for all muscles (all p > 0.1), suggesting inefficacy of the countermeasure in this sample. These findings suggest that prolonged bed rest can result in the atrophy of specific muscles across the hip joint which may affect its stability and function.

Resistive vibration exercise attenuates bone and muscle atrophy in 56 days of bed rest: biochemical markers of bone metabolism

During and after prolonged bed rest, changes in bone metabolic markers occur within 3 days. Resistive vibration exercise during bed rest impedes bone loss and restricts increases in bone resorption markers whilst increasing bone formation. To investigate the effectiveness of a resistive vibration exercise (RVE) countermeasure during prolonged bed rest using serum markers of bone metabolism and whole-body dual X-ray absorptiometry (DXA) as endpoints. Twenty healthy male subjects underwent 8 weeks of bed rest with 12 months follow-up. Ten subjects performed RVE. Blood drawings and DXA measures were conducted regularly during and after bed rest. Bone resorption increased in the CTRL group with a less severe increase in the RVE group (p = 0.0004). Bone formation markers increased in the RVE group but decreased marginally in the CTRL group (p < 0.0001). At the end of bed rest, the CTRL group showed significant loss in leg bone mass (-1.8(0.9)%, p = 0.042) whereas the RVE group did not (-0.7(0.8)%, p = 0.405) although the difference between the groups was not significant (p = 0.12). The results suggest the countermeasure restricts increases in bone resorption, increased bone formation, and reduced bone loss during bed rest.

A Forty-Year Follow-Up of the Dallas Bed Rest and Training Study: The Effect of Age on the Cardiovascular Response to Exercise in Men

In 1966, five 20-year-old men underwent a comprehensive physiological evaluation of the capacity for adaptation of the cardiovascular system in response to 3 weeks of bed rest and 8 weeks of heavy endurance training; these same participants were reevaluated before and after training at the age of 50. The aim of the present study was to reexamine these same men 40 years following the original assessments. In all three studies, minute ventilation and expired gases were analyzed during exercise testing with Douglas bag collection. Cardiac output (CO) was determined using the acetylene rebreathing technique. Compared with the original 30-year interval, the decline in maximal oxygen uptake (VO(2max)) (-11% vs -25%), maximal CO (+6% vs -11%), and maximal stroke volume (+10% vs -10%) were greater between 50 and 60 years of age. The annualized decline in VO(2max) (55 mL/min/y) between ages 50 and 60 was approximately fourfold higher than the decline between 20 and 50 years (12 mL/min/y). In the original five participants of the Dallas Bed Rest and Training Study, VO(2max) declined after 40 years of living due to a balanced decrease in central and peripheral determinants of oxygen uptake. The rate of decline in VO(2max) and its components accelerated after the age of 50 years secondary to age and clinical comorbidities. The net proportional decline in VO(2max) for a period of 40 years of life was comparable with that experienced after 3 weeks of strict bed rest at the age of 20 (27% vs 26%, respectively).

Rowing Ergometer Training During Five Weeks of Head-Down Tilt Bedrest Preserves Cardiac Work and LV Mass

Exercise training in space or during bedrest which recruits both upper and lower body muscle groups may preserve cardiac work and thereby LV structure. PURPOSE: Examine whether rowing ergometry via a periodized exercise training program will not only preserve but increase cardiac work and LV mass. METHODS: Fifteen subjects (14 men and 1 woman, age 20-55 yr) were studied before, during and immediately after 5 weeks of −6° head-down tilt (HDT) bed rest. The subjects were divided into two groups: (1) bed rest without exercise, but sitting upright 45 minutes/day quietly on the ergometer (n=3); (2) bed rest with exercise (30-45 minutes/day, 6 days/week of exercise on a rowing ergometer in addition to 2 days/week of supine resistance training) (n=12). The endurance training included three days of exercise at a moderate, base pace and two days of high intensity interval training followed by a recovery day of intensity below base pace. Ambulatory systolic blood pressure and heart rate were measured over 24 hours before, during and after bed rest (Suntech Accutracker). Stroke volume was measured via acetylene rebreathing technique. Cardiac work was calculated as a product of stroke volume, heart rate, systolic blood pressure and time. RESULTS: Cardiac work of subjects who trained during bed rest was maintained to levels measured prior to bed rest (7.64 + 3.02 vs. 7.71 + 2.14, e08ml·mmHg·day−1). However, the cardiac work of nonexercising subjects decreased during bed rest (7.70 + 1.45 vs. 6.46 + 0.79, e08ml·mmHg·day−1). LV mass was preserved among the exercisers (154 + 58 vs. 157 + 50mg) yet decreased in the non-exercising group (124 + 10 vs. 117 + 1mg). CONCLUSIONS: Cardiac work was preserved in subjects who performed 30-45 min/day of dynamic, rowing exercise combined with resistance training during HDT bed rest. This preservation of cardiac work prevented the cardiac atrophy associated with 5 weeks of bed rest deconditioning. Supported by NASA grant CA00701.

Television Time and Continuous Metabolic Risk in Physically Active Adults

Among Australian adults who met the public health guideline for the minimum health-enhancing levels of physical activity, we examined the dose-response associations of television-viewing time with continuous metabolic risk variables. Data were analyzed on 2031 men and 2033 women aged > or = 25 yr from the 1999-2000 Australian Diabetes, Obesity and Lifestyle study without clinically diagnosed diabetes or heart disease, who reported at least 2.5 h.wk of moderate- to vigorous-intensity physical activity. Waist circumference, resting blood pressure, and fasting and 2-h plasma glucose, triglycerides, and high-density-lipoprotein cholesterol (HDL-C) were measured. The cross-sectional associations of these metabolic variables with quartiles and hours per day of self-reported television-viewing time were examined separately for men and for women. Analyses were adjusted for age, education, income, smoking, diet quality, alcohol intake, parental history of diabetes, and total physical activity time, as well as menopausal status and current use of postmenopausal hormones for women. Significant, detrimental dose-response associations of television-viewing time were observed with waist circumference, systolic blood pressure, and 2-h plasma glucose in men and women, and with fasting plasma glucose, triglycerides, and HDL-C in women. The associations were stronger in women than in men, with significant gender interactions observed for triglycerides and HDL-C. Though waist circumference attenuated the associations, they remained statistically significant for 2-h plasma glucose in men and women, and for triglycerides and HDL-C in women. In a population of healthy Australian adults who met the public health guideline for physical activity, television-viewing time was positively associated with a number of metabolic risk variables. These findings support the case for a concurrent sedentary behavior and health guideline for adults, which is in addition to the public health guideline on physical activity.

Effects of a Comprehensive Exercise Training Regimen and KMgCit on Bone Elasticity as an Indicator of Bone Quality after 5 Weeks of Bedrest

We investigated the effects of a multi‐load exercise program and KMgCit supplementation on the preservation of bone quality following 5 weeks of bedrest as measured by ultrasound critical‐angle reflectometry (UCR). The bone elasticity of 35 subjects (26 M, 9 F, 35 ± 10 yrs) was studied before and after bedrest. The subjects were divided into 4 groups: sedentary with no drug (n=12); sedentary with KMgCit (n=11); exercise (n=11); and exercise with KMgCit (n=4). The exercise group underwent intense multi‐joint rowing ergometry (30–45 min/d, 6 d/wk) and resistive strength training (2 d/wk). Subjects receiving the study drug were given 42:21:63 mEq KMgCit a day. Bone elasticity, a correlate of bone strength, was assessed by UCR on the tibia and calcaneus at multiple angles. In the sedentary group, prolonged bedrest resulted in a small decrease in bone elasticity, most notable in the more responsive trabecular bone (2.5%, 2779±140, 2709±92 m/s, p=0.06). KMgCit increased trabecular elasticity (4.2%, 2705±125, 2814±140 m/s, p&lt;0.05), while exercise showed a similar trend (3.5%, 2701±121, 2798 ±100 m/s, p=0.08). Treatment with both exercise and KMgCit demonstrated a 1.9% increase, but included only 4 subjects. These findings suggest that KMgCit and exercise training are effective countermeasures against trabecular bone quality loss during prolonged periods in microgravity. Supported by NSBRI.

Changes in muscle volume and strength following prolonged bed rest

PURPOSETo determine the effectiveness of dynamic and resistance exercise training in attenuating the loss of structure and functional capacity of skeletal muscle during bed rest.METHODS: Muscle volume and peak torque (Pk T) were assessed before (Pre) and following 5 weeks of −6° head down tilt bed rest in 5 (exercise) and 3 (sedentary group) healthy subjects. Training consisted of rowing (6x/wk) and resistance (2x/wk) training. The sedentary group did no training. Each subject underwent MRI (1.5T) quantification of segmental volumes of 15 contiguous 0.6 cm thick transaxial images of calf and thigh muscles. Peak isokinetic torque during ankle plantar/dorsiflexion and knee extension/flexion was determined. Correlation coefficients for muscle volume and Pk T were determined for leg anti‐gravity muscles.RESULTS: Calf muscle volume decreased slightly by 4% while Pk T increased 31% Pre to Post in the exercise group. In sedentary corresponding values were −15% and −20%. Thigh muscle volume decreased 4% while Pk T decreased 5% Pre to Post in the exercise group. In sedentary corresponding values were −7% and −10%.CONCLUSION: The loss of calf and thigh muscle volume was attenuated but could not be completely eliminated by exercise training during 5 weeks of bed rest. However, muscle function was well preserved with no clinically relevant loss of strength in anti‐gravity muscles.Supported by NASA grant CA00701.

INvestigational Vertebroplasty Efficacy and Safety Trial (INVEST): a randomized controlled trial of percutaneous vertebroplasty

BackgroundThe treatment of painful osteoporotic vertebral compression fractures has historically been limited to several weeks of bed rest, anti-inflammatory and analgesic medications, calcitonin injections, or external bracing. Percutaneous vertebroplasty (the injection of bone cement into the fractured vertebral body) is a relatively new procedure used to treat these fractures. There is increasing interest to examine the efficacy and safety of percutaneous vertebroplasty and to study the possibility of a placebo effect or whether the pain relief is from local anesthetics placed directly on the bone during the vertebroplasty procedure.Methods/DesignsOur goal is to test the hypothesis that patients with painful osteoporotic vertebral compression fractures who undergo vertebroplasty have less disability and pain at 1 month than patients who undergo a control intervention. The control intervention is placement of local anesthesia near the fracture, without placement of cement. One hundred sixty-six patients with painful osteoporotic vertebral compression fractures will be recruited over 5 years from US and foreign sites performing the vertebroplasty procedure. We will exclude patients with malignant tumor deposit (multiple myeloma), tumor mass or tumor extension into the epidural space at the level of the fracture.We will randomly assign participants to receive either vertebroplasty or the control intervention.Subjects will complete a battery of validated, standardized measures of pain, functional disability, and health related quality of life at baseline and at post-randomization time points (days 1, 2, 3, and 14, and months 1, 3, 6, and 12). Both subjects and research interviewers performing the follow-up assessments will be blinded to the randomization assignment. Subjects will have a clinic visit at months 1 and 12. Spine X-rays will be obtained at the end of the study (month 12) to determine subsequent fracture rates. Our co-primary outcomes are the modified Roland score and pain numerical rating scale at 1 month.DiscussionAlthough extensively utilized throughout North America for palliation of pain, vertebroplasty still has not undergone rigorous study. The study outlined above represents the first randomized, controlled study that can account for a placebo effect in the setting of vertebroplasty.Trial RegistrationCurrent Controlled Trials ISRCTN81871888

Acute Spontaneous Spinal Subdural Hematoma Presenting as Paraplegia

Case report. To report an unusual case of spontaneous spinal subdural hematoma and to review relevant literature and discuss the etiology, pathogenesis, clinical features, imaging, and prognosis. Spontaneous spinal subdural hematoma with no underline pathology is a very rare condition. Only 19 cases have been previously reported. The case of a 44-year-old man is presented. Pubmed (Medline) was used to search publications. Our patient presented with sudden severe low back pain following a minimal effort, with rapid onset of complete paraplegia. MRI revealed an anterior subdural hematoma from T2-T6 with cord compression. An urgent laminectomy was performed. MRI scan, surgery, and CT angiogram did not reveal any underlying pathology to account for the subdural hematoma. The patient demonstrated substantial clinical improvement after 6 weeks of bed rest and intense rehabilitation program. Spinal subdural hematoma (SSDH) is uncommon and can be caused by abnormalities of coagulation, blood dyscrasias, or trauma, underlying neoplasm, and arteriovenous malformation. SSDH is very rare in the absence of these underlying conditions. It occurs most commonly in the thoracic spine and presents with sudden back pain radiating to the arms, legs or trunk, varying degrees of motor, sensory, and autonomic disturbances. On MRI, SSDH is seen as a space-occupying lesion, usually ventrally, contained within the dura matter, and can demonstrate variable T1 and T2 signal depending on the age of the hematoma. The prognosis is variable. The majority of cases in the literature had surgical decompression, although cases that were managed conservatively have been reported to be successful as well. The indications of surgery need to be clarified.

Low energy dislocation of the hip joint in an adult with hereditary multiple exostosis

This article will describe the incidence of a low-energy hip dislocation, due to a fall from a standing height, in a 64-year-old female with hereditary multiple exostosis (HME). The dislocated left hip was reduced under spinal anesthesia, and the patient was restricted to 3 weeks of bed rest with skeletal traction of the affected limb. The post-reduction CT scan revealed a tangential fracture in the apex of the exostosis on the posteroinferior aspect of the femoral neck. The exostosis was assumed to impinge on the ischium and that the lever mechanism led to the dislocation. The 3 month follow-up MRI revealed no evidence of subluxation or avascular necrosis of the femoral head.

Magnetic Resonance Imaging Assessment of Trunk Muscles During Prolonged Bed Rest

Prospective longitudinal study. OBJECTIVE.: To investigate, using magnetic resonance imaging (MRI), the influence of bed rest on the lumbopelvic musculature. Reduced gravitational loading and inactivity (bed rest) are known to result in significant change in musculoskeletal function, although little is known about its effects on specific muscles of the lumbopelvic region. Ten healthy male subjects underwent 8 weeks of bed rest with 6 months of follow-up. MRI of the lumbopelvic region was conducted at regular time-points during and after bed rest. Using uniplanar images at L4, cross-sectional areas (CSAs) of the multifidus, lumbar erector spinae, quadratus lumborum, psoas, anterolateral abdominal, and rectus abdominis muscles were measured. Multifidus CSA decreased by day 14 of bed rest (F = 7.4, P = 0.04). The lumbar erector spinae and quadratus lumborum CSA showed no statistically significant difference to baseline across the time of bed rest (P > 0.05). The anterolateral abdominal, rectus abdominis, and psoas CSA all increased over this time. Psoas CSA increased by day 14 (F = 6.9, P = 0.047) and remained so until day 56, whereas the anterolateral abdominal CSA (F = 29.4, P = 0.003) and rectus abdominis CSA (F = 8.9, P = 0.03) were not statistically larger than baseline until day 56. On reambulation after completion of the bed rest phase, multifidus, anterolateral abdominal, and rectus abdominis CSA returned to baseline levels (P > 0.05) by day 4 of follow-up, whereas psoas CSA returned to baseline level after day 28 of the follow-up period. Bed rest resulted in selective atrophy of the multifidus muscle. An increased CSA of the trunk flexor musculature (increases in psoas, anterolateral abdominal, and rectus abdominis muscles) may reflect muscle shortening or possible overactivity during bed rest. Some of the changes resemble those seen in low back pain and may in part explain the negative effects of bed rest seen in low back pain sufferers.

High-density surface EMG study on the time course of central nervous and peripheral neuromuscular changes during 8 weeks of bed rest with or without resistive vibration exercise

The aim of the present study was to assess the time course and the origin of adaptations in neuromuscular function as a consequence of prolonged bed rest with or without countermeasure. Twenty healthy males volunteered to participate in the present study and were randomly assigned to either an inactive control group (Ctrl) or to a resistive vibration exercise (RVE) group. Prior to, and seven times during bed rest, we recorded high-density surface electromyogram (sEMG) signals from the vastus lateralis muscle during isometric knee extension exercise at a range of contraction intensities (5–100% of maximal voluntary isometric torque). The high-density sEMG signals were analyzed for amplitude (root mean square, RMS), frequency content (median frequency, F med) and muscle fiber conduction velocity (MFCV) in an attempt to describe bed rest-induced changes in neural activation properties at the levels of the motor control and muscle fibers. Without countermeasures, bed rest resulted in a significant progressive decline in maximal isometric knee extension strength, whereas RMS remained unaltered throughout the bed rest period. In line with observed muscle atrophy, both F med and MFCV declined during bed rest. RVE training during bed rest resulted in maintained maximal isometric knee extension strength, and a strong increase (∼30%) in maximal EMG amplitude, from 10 days of bed rest on. Exclusion of other factors led to the conclusion that the RVE training increased motor unit firing rates as a consequence of an increased excitability of motor neurons. An increased firing rate might have been essential under training sessions, but it did not affect isometric voluntary torque capacity.

Natural Calcium Isotopic Composition of Urine as a Marker of Bone Mineral Balance

We investigated whether changes in the natural isotopic composition of calcium in human urine track changes in net bone mineral balance, as predicted by a model of calcium isotopic behavior in vertebrates. If so, isotopic analysis of natural urine or blood calcium could be used to monitor short-term changes in bone mineral balance that cannot be detected with other techniques. Calcium isotopic compositions are expressed as delta(44)Ca, or the difference in parts per thousand between the (44)Ca/(40)Ca of a sample and the (44)Ca/(40)Ca of a standard reference material. delta(44)Ca was measured in urine samples from 10 persons who participated in a study of the effectiveness of countermeasures to bone loss in spaceflight, in which 17 weeks of bed rest was used to induce bone loss. Study participants were assigned to 1 of 3 treatment groups: controls received no treatment, one treatment group received alendronate, and another group performed resistive exercise. Measurements were made on urine samples collected before, at 2 or 3 points during, and after bed rest. Urine delta(44)Ca values during bed rest were lower in controls than in individuals treated with alendronate (P <0.05, ANOVA) or exercise (P <0.05), and lower than the control group baseline (P <0.05, t-test). Results were consistent with the model and with biochemical and bone mineral density data. Results confirm the predicted relationship between bone mineral balance and calcium isotopes, suggesting that calcium isotopic analysis of urine might be refined into a clinical and research tool.

Reduction of Renal Stone Risk by Potassium-Magnesium Citrate During 5 Weeks of Bed Rest

Exposure to the microgravity environment of space increases the risk of kidney stone formation, particularly for calcium oxalate and uric acid stones. This study was performed to evaluate the efficacy of potassium alkali as potassium-magnesium citrate in reducing renal stone risk and bone turnover. This study was performed as a double-blind, placebo controlled trial. We studied 20 normocalciuric subjects randomized to either placebo or potassium-magnesium citrate (42 mEq potassium, 21 mEq magnesium, 63 mEq citrate per day) before and during 5 weeks of strict bed rest. The study was performed in the General Clinical Research Center and under a controlled dietary regimen composed of 100 mEq of sodium, 800 mg of calcium, 0.8 gm/kg animal protein and 2,200 kcal per day. Two 24-hour urine collections were obtained under oil each week for assessment of stone risk parameters and relative saturation of calcium oxalate, brushite and undissociated uric acid. Blood was also collected for determination of serum immunoreactive parathyroid hormone and vitamin D metabolites. Bed rest promoted a rapid increase in urinary calcium excretion of approximately 50 mg per day in both groups. Despite this increase subjects treated with potassium-magnesium citrate demonstrated significant decreases in the relative saturation of calcium oxalate and in the concentration of undissociated uric acid compared to placebo. Immunoreactive parathyroid hormone, serum 1,25-dihydroxyvitamin D and intestinal calcium absorption all decreased in both groups with no difference in response between the 2 treatment arms. Provision of alkali as potassium-magnesium citrate is an effective countermeasure for the increased risk of renal stone disease associated with immobilization. Despite an increase in urine calcium concentration, the relative saturation of calcium oxalate decreased due to citrate chelation of calcium and the concentration of undissociated uric acid decreased due to the significant increase in urine pH.

A 40-year Follow-up of the Dallas Bed Rest Study

BACKGROUND: In 1966, five 20-year old men underwent a comprehensive physiologic evaluation of the capacity for adaptation of the cardiovascular system in response to 3 weeks of bed rest and 8 weeks of heavy aerobic training; these same subjects were studied again at the age of 50. The aim of the present study was to re-examine the cardiovascular response to maximal exercise in these men after a 40-year interval from their initial assessments. METHODS: In all three study years, minute ventilation and expired gases were determined with Douglas bags and mass spectrometry respectively. Cardiac output was determined using the C2H2 re-breathe technique in 1996 and 2006. RESULTS: On average, compared with 1966, body weight and percent fat mass increased 19 and 73% respectively, while lean body mass declined 10%. Additionally, absolute VO2max decreased 28% (3.3 vs 2.4 L/min), attributable to a 22% decline in maximal arterio-venous oxygen difference (16.2 vs 12.7 vol%). Age-related changes in cardiovascular capacity were significantly greater in the interval between 1996 and 2006 compared with the interval between 1966 and 1996 (Table 1).Table 1: Relative changes in select variables between the two follow-up intervals.CONCLUSIONS: In the original 5 participants of the Dallas Bed Rest Study, maximal oxygen uptake declined over the 40-year study interval, initially because of a reduction in maximal peripheral oxygen extraction, and subsequently due to a balanced decrease in delivery and extraction. Also, the rate of decline in VO2max and its determinants accelerated after the age of 50 years. Impressively, the decline in VO2max after 40 years of life was comparable (27% vs 26%) to that experienced after three weeks of strict bed rest at 20 years of age.

Tonic-to-phasic shift of lumbo-pelvic muscle activity during 8 weeks of bed rest and 6-months follow up

Prior motor control studies in unloading have shown a tonic-to-phasic shift in muscle activation, particularly in the short extensors. Tonic muscle activity is considered critical for normal musculoskeletal function. The shift from tonic-to-phasic muscle activity has not been systematically studied in humans in unloading nor at the lumbo-pelvic (LP) region. Ten healthy young male subjects underwent 8 wk of bed rest with 6-mo follow up as part of the "Berlin Bed-Rest Study." A repetitive knee movement model performed in the prone position is used to stimulate tonic holding LP muscle activity, as measured by superficial EMG. Tonic and phasic activation patterns were quantified by relative height of burst vs. baseline electromyographic linear-envelope signal components. Statistical analysis shows a shift toward greater phasic activity during bed rest and follow up (P < 0.001) with a significant interaction across muscles (P < 0.001) specifically affecting the short lumbar extensors. These changes appear unrelated to skill acquisition over time (P all > or = 0.196). This change of a shift from tonic LP muscle activation to phasic is in line with prior research on the effects of reduced weight bearing on motor control.

Superficial Lumbopelvic Muscle Overactivity and Decreased Cocontraction After 8 Weeks of Bed Rest

Longitudinal study. To gain insight into the effects of inactivity on lumbopelvic stabilization. Some authors have suggested a link between inactivity and lumbopelvic (LP) pain. Studies examining the superficial musculature in LP pain have shown overactivity and increased cocontraction. Studies in inactivity (bed rest, microgravity) have shown similar effects on the musculature of the legs. Here we examine the effect of bed rest on superficial LP activity and cocontraction. Ten male subjects participated in the "Berlin Bed Rest Study" and underwent 8 weeks of bed rest with a 1-year follow-up. A repetitive knee movement model at four movement speeds in non-weightbearing was used to assess, via electromyography, activity (amplitude-ratios) in five superficial LP muscles and abdominal flexor-lumbar extensor cocontraction for LP stabilization. Testing was conducted at regular intervals during and after bed rest. Analysis of the amplitude-ratio data showed a significant effect of testing date (F = 2.38, P = 0.005). This effect was generalized across all muscles, however (F = 0.59, P = 0.989). During bed rest, subjects exhibited higher levels of activity but lower levels of cocontraction (F = 8.84, P < 0.001), and the changes were still present up to 1 year after bed rest. The bed rest protocol resulted in the development of superficial muscle overactivity but decreased cocontraction. These changes could reflect dysfunction of central nervous system control of LP stabilization. These changes were still apparent 1 year after bed rest, suggesting a stable change in motor control.

Lower body negative pressure treadmill exercise as a countermeasure for bed rest-induced bone loss in female identical twins

Supine weight-bearing exercise within lower body negative pressure (LBNP) alleviates some of the skeletal deconditioning induced by simulated weightlessness in men. We examined this potential beneficial effect in women. Because dietary acid load affected the degree of bone resorption in men during bed rest, we also investigated this variable in women. Subjects were 7 pairs of female identical twins assigned at random to 2 groups, sedentary bed rest (control) or bed rest with supine treadmill exercise within LBNP. Dietary intake was controlled and monitored. Urinary calcium and markers of bone resorption were measured before bed rest and on bed rest days 5/6, 12/13, 19/20, and 26/27. Bone mineral content was assessed by dual-energy X-ray absorptiometry before and after bed rest. Data were analyzed by repeated-measures two-way analysis of variance. Pearson correlation coefficients were used to define the relationships between diet and markers of bone metabolism and to estimate heritability of markers. During bed rest, all markers of bone resorption and urinary calcium and phosphorus increased ( P < 0.001); parathyroid hormone ( P = 0.06), bone-specific alkaline phosphatase ( P = 0.06), and 1,25-dihydroxyvitamin D ( P = 0.09) tended to decrease. LBNP exercise tended to mitigate bone density loss. The ratio of dietary animal protein to potassium was positively correlated with urinary calcium excretion for all weeks of bed rest in the control group, but only during weeks 1 and 3 in the exercise group. Pre-bed rest data suggested that many markers of bone metabolism have strong genetic determinants. Treadmill exercise within LBNP had less of a protective effect on bone resorption during bed rest in women than previously published results had shown for its effect in men, but the same trends were observed for both sexes. Dietary acid load of these female subjects was significantly correlated with calcium excretion but not with other bone resorption markers.

Importance of Resistance Training for Patients After a Cardiac Event

After a myocardial infarction (MI), percutaneous coronary intervention, or angina pectoris, patients receive conflicting advice from physicians about the level of activity that is acceptable. Most are told that they should not lift anything >5 pounds. When we conducted an informal survey of 28 patients from the Cardiac Rehabilitation Department at the Baylor Jack and Jane Hamilton Heart and Vascular Hospital, patients also recollected advice such as not to lift >10 pounds “for a while,” not to lift anything for a week, not to drive more than 30 minutes, not to “get exhausted” for a month, not to exercise for a few weeks, and not to lift >25 pounds for a period of time—or ever. These guidelines are not only confusing but can also promote fear and inactivity. Further complicating the scenario is that while physicians typically prescribe aerobic exercise—and particularly walking—for the purpose of avoiding further heart complications, patients are more interested in being able to return to activities of daily living, such as mowing the lawn, lifting grandchildren, or vacuuming. The resistance training that would lead to that outcome is rarely prescribed. Exercise physiologists, cardiac rehabilitation professionals, and personal trainers focus on three principles in training. One such principle is specificity. This principle indicates that the training effect is limited to the muscle fibers involved in the activity. For example, mitochondria adapt to endurance training, and contractile proteins adapt to resistance training. It is not reasonable to expect the arms to become trained during a 10-weekjogging program, for example(1). When the specificity principle was applied to football, coaches moved from mile runs for training to 100-yard runs, simulating the longest distance a player would run in competition. The other two principles of fitness training are overload, which states that for a training effect to occur, a tissue must be challenged with an intensity, duration, or frequency to which it is not accustomed; and reversibility, which states that training gains are quickly lost when the overload is removed (1). Over time, positive gains have been made in motivating patients to become more active following MI. Just 40 years ago, patients were put on bedrest for 4 to 6 weeks after an MI. Since then, it has been shown that after just a few days or weeks of bedrest, the patient experiences decreased cardiorespiratory fitness, strength, and flexibility (2). While physicians now acknowledge the value of exercise in cardiac rehabilitation, they have been hesitant to allow resistance training. Part of the problem is the existing guidelines (Table ​(Table11). In our opinion, these guidelines not only delay resistance training unnecessarily but also prescribe weight amounts that are below what patients need for even the most basic activities of daily living. We argue that resistance training should be promoted following the principle of specificity—that is, based on the fact that most patients set goals not to run a 10-kilometer race or to go mountain biking but rather to rise from the bathtub or mow the lawn. The constraints faced in cardiac rehabilitation, from physician prescriptions and from the guidelines, are particularly worrisome, since in society today we seem to place more importance on specifically training athletes (cyclists, marathon runners, football players) than we do on appropriately preparing patients to safely perform everyday activities. This limitation has become particularly obvious as cardiac rehabilitation patients have become younger. Some of these patients need to return to firefighting, police work, or other physically stressful jobs. Table 1 Cardiac rehabilitation resistance training guidelines by diagnosis∗ Our reasons for promoting resistance training are presented below.