Osteoporos Int (2010) 21:597–607 DOI 10.1007/s00198-009-0985-z
ORIGINAL ARTICLE
Resistive vibration exercise attenuates bone and muscle atrophy in 56 days of bed rest: biochemical markers of bone metabolism G. Armbrecht & D. L. Belavý & U. Gast & M. Bongrazio & F. Touby & G. Beller & H. J. Roth & F. H. Perschel & J. Rittweger & D. Felsenberg
Received: 8 February 2009 / Accepted: 28 May 2009 / Published online: 18 June 2009 # International Osteoporosis Foundation and National Osteoporosis Foundation 2009
Abstract Summary 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. Introduction 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. Methods 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. G. Armbrecht (*) : D. L. Belavý : U. Gast : M. Bongrazio : F. Touby : G. Beller : D. Felsenberg Zentrum für Muskel- und Knochenforschung, Charité Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany e-mail:
[email protected] H. J. Roth Labor Limbach, Abteilung für Endokrinologie und Onkologie, Im Breitspiel 15, 69126 Heidelberg, Germany F. H. Perschel Zentralinstitut für Laboratoriumsmedizin und Pathobiochemie, Charité Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany J. Rittweger Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Oxford Road, Manchester M1 5GD, UK
Results 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). Conclusions The results suggest the countermeasure restricts increases in bone resorption, increased bone formation, and reduced bone loss during bed rest. Keywords Bone turnover markers . DXA . Microgravity . Re-ambulation . Vibration exercise
Introduction With space agencies and governments striving for manned missions to Mars, an important research question is the development of appropriate countermeasures to maintain the function of the musculoskeletal system upon landing. Excessive loss in bone strength, with potential risk for fracture after such long-term flights, would threaten mission success. Earlier studies on astronauts and cosmonauts have shown that aerobic exercise countermeasures do little to prevent bone atrophy in spaceflight [1–3], but that groundbased works to date find resistance exercise to be more efficient in preventing musculoskeletal deconditioning [4, 5]. Indeed, when considering the degree of loading, evidence suggests that, all other factors being equal, bone tissue reacts more to peak forces, rather than the average force over time [6]. In line with the opinion of other authors [7–9], it appears that resistance exercise is the way forward
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in preventing bone and muscle deconditioning during spaceflight and microgravity simulation (bed rest). Recently, however, whole-body vibration has received greater attention in exercise and rehabilitation [10]. A number of studies have shown vibration exercise to facilitate neuromuscular performance [11–15], and it is thought to stimulate additional muscle activity via the muscle spindle system [16, 17]. Vibratory stimuli are transmitted beyond the calf region up into the thigh and hip region [18, 19]. Vibratory input during resistance exercise could provide an additional stimulus for force development and hence stimulus for bone and muscle maintenance during prolonged bed rest. Metabolic markers of bone turnover have provided valuable information in monitoring the effects of spaceflight, immobilization, and countermeasures on bone. Typically, in both spaceflight and bed rest, increases in the levels of markers reflecting bone resorption are seen, but with little change in markers of bone formation [20– 26]. This pattern of changes suggests bone resorption drives bone loss in bed rest and that any countermeasure would affect primarily bone resorption rather than formation. However, a resistive exercise regimen that efficiently prevented bone loss in human bed rest was associated with increased blood levels of the bone formation markers, bonespecific alkaline phosphatase and osteocalcin [5]. Whereas markers of bone metabolism give information as to whether bone is being remodeled, they do not show where bone loss occurs. Whole-body dual X-ray absorptiometry (DXA), on the other hand, can be used quite well to investigate bone (and muscle) loss in different body regions during spaceflight and bed rest [2, 3, 5, 21] and has been used in bed-rest studies to assess the effectiveness of countermeasures [5, 21]. DXA may be considered an appropriate methodology to complement markers of bone metabolism in monitoring the effectiveness of countermeasures in bed rest. The main aim of this study was to assess the effectiveness of a resistive vibration exercise (RVE) countermeasure against bone and muscle deconditioning during prolonged (56 days) of bed rest, by means of metabolic markers of bone turnover and whole-body DXA.
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elsewhere [27]. In brief, subjects were randomly allocated to either a group that remained inactive (control, CTRL group; N=10; age (mean(SD))=33.4(6.6)years; height=185(7)cm; weight=79.4(9.7)kg) or a group that underwent a wholebody resistive vibration exercise countermeasure program (RVE group; N=10; age=32.6(4.8)years; height=183(9)cm, weight=81.7(14.4)kg) using the Galileo Space exercise device (Novotec Medical, Pforzheim, Germany). Horizontal bed rest was employed, though subjects were permitted to be positioned in up to 30° head-up tilt for recreational activities during daylight hours (such as watching television). Subjects performed all hygiene in the supine position and were discouraged from moving excessively or unnecessarily. Force sensors placed in the bed supports and video surveillance permitted monitoring of subjects’ activities. The institutional ethics committee approved this study and subjects gave their informed written consent. The Bundesamt für Strahlenschutz gave its approval for the radiological examinations conducted in this study. Countermeasure exercise
Materials and methods
Resistive vibration exercise (RVE) was performed using a dedicated prototype (Galileo Space) of a commercially available vibration platform (Novotec Medical). The exercise device permitted exercise in supine position throughout bed rest. The exercise regime targeted the lower leg muscle groups with resistive loading and neuromuscular stimuli via wholebody vibration applied at the feet [28, 29]. The countermeasure exercise protocol is described in detail elsewhere [27]. In brief, the subjects were placed in supine position (Fig. 1), with an applied vibration amplitude between 3.5 and 4 mm. An axial force between 1.0 and 1.8 times body weight was placed through the subjects’ trunk and spine via elastic shoulder straps (targeted to be approximately 75–85% of the subject’s one-repetition maximum). With the exception of Sundays and Wednesday afternoons, two exercise sessions per day, of 30 min duration (between 4 and 6 min pure exercise time) were performed. A total of 89 exercise sessions were scheduled for each subject. Trained staff supervised all training sessions, and subjects were given feedback and encouragement to perform optimally. For each morning session, four resistive exercises were performed once in the following order:
Bed-rest protocol
&
The “Berlin Bed-Rest Study” was undertaken at the Charité Campus Benjamin Franklin Hospital in Berlin, Germany, from February 2003 to June 2005. Twenty male subjects underwent 8 weeks of strict bed rest with a subsequent 12month follow-up recovery period. The bed-rest protocol, as well as inclusion and exclusion criteria, is discussed in detail
&
Squatting: knees were stretched from 90° to full extension in cycles of 6 s for 60 s whilst the vibration frequency was progressed from 18 Hz at the beginning of bed rest up to a maximum of 24 Hz; Heel raises: with the knees in almost complete extension, the heels were raised into ankle plantar flexion as long as the subjects could sustain this (up to 40 s). The vibration frequency was retained at 26 Hz.
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Fig. 1 Resistive vibration Subjects were required to force transmitted via belts grips. Vibratory stimuli in
& &
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exercise countermeasure during bed rest. perform leg exercises against a resistive at the waist and shoulders and via hand the legs are generated by rotation of the
suspended platform around a vertically oriented axis. Axial loading of the spine occurs via the shoulder straps. Figures at right of image indicate how the amplitude of vibration is modified by foot position
Toe raises: with knees in complete extension, the forefoot raised into ankle dorsiflexion up to 40 s. The vibration frequency was retained at 26 Hz. Explosive kicks: ten explosive pushes against the vibrating platform were performed. These “kicks” were targeted at generating peak forces to stimulate bone retention rather than muscle per se.
of bone turnover were selected: bone-specific alkaline phosphatase (BAP; bone formation), total aminoterminal propeptide of type I collagen (PINP; bone formation), Cterminal cross-linking telopeptide of type I collagen (CTX; bone resorption), and tartrate-resistant acid phosphatase 5b (TRACP 5b; osteoclast activity). Intact parathyroid hormone (iPTH) was also analyzed. iPTH, PINP, and CTX were measured by means of an automated electrochemiluminescence immunoassay (ECLIA; Modular Analytics E170, Roche Diagnostics, Penzberg, Germany), BAP by means of a paramagnetic particle chemiluminescent immunoassay (Access OSTASE; Access Immunoassay System, Beckman Coulter GmbH, Krefeld, Germany), and TRACP 5b by means of a solid-phase immunofixed enzyme activity assay (Immunodiagnostic Systems [IDS], Boldon, UK). Serum calcium was measured by means of an automated clinical chemistry analyzer (Modular Analytics; Roche Diagnostics, Mannheim, Germany). All analytical platforms and immunoassays were used in the laboratory for routine testing and all assays were performed in one batch (i.e., after collection of all serum samples). They were run strictly in accordance with the guidelines given by the manufacturers and were subject to continuous maintenance and service according to the laboratory standard operating procedures for good laboratory practice.
In the afternoon session, subjects were asked to exercise with a lower resting platform reaction force (60–80% of the value achieved in the morning). Only one exercise was performed and subjects retained their feet on the platform in nearly extended position without movement. Frequency was retained at 19 Hz and the exercise performed between 4 and 6 min (depending on physical ability of subject). Blood drawings Venous blood samples were taken between 7 and 8 A.M. after 12 h in a fasting state during baseline collection at BDC-2, on days BR1, BR3, BR5, BR12, BR19, BR26, BR33, BR40, BR47, and BR56 of the bed rest, and on R+ 1, R+3, R+7, R+28, R+90, and R+180 during recovery phase. The consistent morning time for blood drawing was chosen due to the importance of the circadian rhythm for certain parameters (e.g., parathyroid hormone). Thirty minutes after drawing, samples were centrifuged at 3,500 rpm for 10 min, serum was obtained and stored at −80°C until analysis. To eliminate inter-assay variation, all serum samples were analyzed in one batch at the conclusion of all blood collections (Labor Limbach, Heidelberg, Germany). Biochemical markers of bone turnover Recommended biochemical markers were chosen to monitor bone turnover [30]. The following biochemical markers
Urine collection and analyses To assess changes in the amount of calcium excreted by the body, daily urine collections were performed. Urine was collected from 8 A.M. 2 days prior to the beginning of bed rest (BDC-2). Urine bottles were emptied regularly over the course of the day into larger collecting flasks by the nursing staff. Every 24 h (at 8 A.M.), the subject was requested again to void his urinary bladder and the total volume over the 24-h period was measured. Aliquots were taken from each
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daily collection and stored at −80°C. To avoid precipitation of calcium salts, samples were acidified using HCl. Calcium levels in each sample were measured by atomic absorption spectrophotometry (Unicam 9200 PX, Philips, Kassel, Germany).
measurement sessions were undertaken on the same subjects, a Bonferroni adjustment was not performed; rather, we looked for consistent significant differences across time points.
Whole-body composition
Results
DXA (Delphi W; Hologic, Waltham, MA, USA) total body scans were performed according to the standard Hologic Operator’s Manual during baseline collection (BDC) 3 days prior to the start of bed rest (BDC-3), on bed rest (BR) days BR2, BR17, BR31, BR45, and BR55, and on post-bed-rest recovery (R+) days R+14, R+28, R+90, R+180, and R+360. Bone mass (g) and lean tissue mass (g) in the arm, leg, trunk, and head sub-regions were derived from the whole-body scan. Due to the height of the subjects and the technical requirements of the scanner, it was not possible to include the head in a number of subjects during measurement. Thus, in the whole-body composition data presented here, we excluded the head data in all subjects (i.e., subtotal values). As the right leg was tested in other experiments involving leg muscle isometric contraction [31, 32] or knee movement [33, 34] during the bed-rest phase, only the left leg was considered in analyses of individual subregions in the DXA data. All scanning and analyses were performed by the same operator to ensure consistency and followed standard quality control procedures.
Table 1 shows the number of subjects whose data sets were available for analysis at each study date. In the baseline data of the biochemical markers of bone metabolism (Table 2), PINP was marginally (p=0.044) higher in the CTRL group at baseline, with TRACP 5b being much higher (p=0.0006) in the CTRL group. No evidence existed for differences in the baseline values of any of the other markers (p all ≥0.088). Baseline values of the DXA measurement (no differences in between the two groups at baseline; p all ≥0.214) are shown in Tables 3 and 4.
Statistical analysis Linear mixed-effects models were employed in statistical analysis [35]. For all variables except urinary calcium excretion (which was measured up to 4 days after bed rest; R+4), separate statistical models were built for the bed-rest and recovery phases. In analysis of variance (ANOVA) of the bone and lean mass DXA data, fixed effects of subject group (CTRL, RVE), sub-region (arm, trunk, leg), and study date as well as up to a three-way interaction between these variables were used. Whole-body (sub-total, without head) DXA bone mass data, biochemical markers of bone metabolism (PINP, BAP, CTX, TRACP 5b, iPTH, and serum calcium), and urine excretion of calcium were analyzed with fixed effects of subject group and study date as well as their two-way interaction. Where necessary, allowances were made for heterogeneity of variance (such as due to subject group, sub-region, or as a function of the value fitted by the statistical model). Including baseline (BDC) data as a covariate in ANOVA did not alter any of the results. The “R” statistical environment (version 2.4.1, www. r-project.org) was used to implement these analyses. An α of 0.05 was taken for statistical significance. As multiple
Biochemical markers of bone metabolism In the bed-rest phase of the study, PINP (bone formation), CTX (bone resorption), TRACP 5b (osteoclast activity), and iPTH (calcium regulation) all showed significant changes over the course of the study (study date[BDC to R+1]; F all ≥7.4, p all ≤0.0008; Figs. 2 and 3). When considering the two subject groups, PINP, BAP, and CTX showed a different Table 1 Number of subjects’ data sets available for analysis at each study date DXA
Bone metabolism
Study date BDC-3
CTRL 10
RVE 10
CTRL 10 10 10 10 10 10
RVE 10 10 10 10 10 10
Study date BDC-2 BR1 BR3 BR5 BR12 BR19
BR2
10
10
BR17
10
10
BR31
10
10 10 10
10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10
BR26 BR33 BR40 BR47 BR56 R+1 R+3 R+7
BR45 BR55
10 10
R+14 R+28 R+90 R+180 R+360
9 10 10 9 9
9 9 9 10 9
10 10 9
9 9 10
R+28 R+90 R+180
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Table 2 Baseline (BDC-2) levels of biochemical markers of bone metabolism
Table 4 Sub-total (without head) bone mass over the course of the study
Parameter
Study date
Subject group
PINP [µg/l] BAP [µg/l] CTX [µg/l] TRACP5b [U/l] iPTH [ng/l] Calcium serum [mmol/l] Calcium excretion [mmol/day]
CTRL
RVE
78.7 13.6 0.67 3.94 28.9 2.34 4.0
53.2 11.9 0.51 3.00 26.8 2.29 5.2
(31.8) (4.5) (0.21) (0.63) (8.0) (0.11) (1.9)
CTRL (19.1)* (2.8) (0.17) (0.35)** (8.7) (0.08) (2.5)
Values are mean (SD) *p=0.044 and **p=0.0006 for differences between groups. All other variables p≥0.088
response between the RVE and CTRL groups in the bed-rest phase of the study (group×study date[BDC to R+1]; F all ≥2.1, p all ≤0.019; Fig. 2). TRACP 5b and iPTH did not (group× study date[BDC to R+1]; F both <1.6, p both ≥0.11; Fig. 2). During bed rest, either no change, or a marginal decrease, in bone formation (PINP, BAP) is seen in the CTRL group (Fig. 2). Bone resorption (CTX) was less in the RVE group than in the CTRL group during bed rest and osteoclastic activity (TRACP 5b) was similar in both groups (Fig. 2). iPTH decreased in the CTRL group, with no change in the RVE group (Fig. 3), although the differences between the groups were not statistically significant in ANOVA. In the recovery phase, evidence existed for changes in all of the parameters considered (study date[R+ 1 to R+180]; F all ≥2.8, p all ≤0.022; Figs. 2 and 3). A different response between the RVE and CTRL groups in the recovery phase was seen for PINP, BAP, CTX, and iPTH (group×study date[R+ 1 to R+180]; F all >2.9, p all ≤0.017), but not TRACP 5b (group×study date[R+1 to R+180]; F=0.7, p=0.62). PINP Table 3 Baseline (BDC-3 and BR2 pooled) values of DXA data in each subject group and body region Body region
Bone mass Arm Leg Trunk Lean mass Arm Leg Trunk
Baseline BR18 BR31 BR44 BR55 R+14 R+28 R+90 R+180 R+360
2,423.9 2,422.0 2,408.3 2,396.6 2,396.2 2,413.7 2,408.1 2,405.6 2,414.9 2,435.8
RVE (128.7) (11.4) (7.5)* (10.1)** (9.7)** (10.2) (9.1) (13.0) (9.5) (12.3)
2,401.3 2,406.4 2,393.4 2,378.5 2,387.4 2,390.5 2,396.9 2,401.7 2,409.5 2,420.8
(128.7) (14.0) (10.9) (9.9)* (10.4) (10.0) (9.4) (10.0) (15.3) (14.1)
All values are in grams. Baseline values are mean (SEM) of pooled data from BDC and BR2. Subsequently, values are mean and standard error of the mean difference to baseline. Significance indicated by: *p<0.05; **p<0.01 BRday of bed rest, R+ day of recovery
levels in the RVE group remaining at the (increased) bedrest levels up until 28 days after bed rest and the CTRL group showed increases in PINP above its (marginally decreased) end of bed-rest level by R+28 (Fig. 2). BAP actually decreased further in the CTRL group after the end of bed rest and was only increased above baseline levels by R+28. The RVE group retained their end of bed-rest (increased) levels of BAP, with further increases being seen at R+28. Ninety days (R+90) after bed rest, BAP was still increased in both groups. Bone resorption (CTX) shows returns to its pre-bed-rest levels within 7 days of bed rest in both the RVE and CTRL groups. Osteoclastic activity (TRACP 5b) also decreases rapidly after bed rest, although it remains marginally increased in the recovery phase. In recovery, iPTH increased in the CTRL and RVE groups in the first week, with elevated values observed beyond this (Fig. 3). Calcium in serum and urine
Subject group CTRL
Group
RVE
224.7 (24.3) 597.3 (76.2) 779.2 (114.7)
216.3 (46.5) 568.8 (93.7) 808.8 (204.9)
3,604.0 (337.9) 10,208.0 (856.2) 29,787.3 (2,857.8)
3,439.8 (438.5) 9,860.3 (992.5) 29,413.7 (3,768.0)
Values are mean (SD) in grams (g). No statistical differences between groups at baseline (p all ≥0.214)
Serum levels of calcium changed during bed rest (study date[BDC to R+1]; F=5.6, p<0.0001) and recovery (study date[R+ 1 to R+ 180]; F=4.2, p=0.0019) but with no difference between the two groups (group×study date=F both <1.1, p both >0.41). Whilst post hoc contrasts show significant changes in serum calcium levels (Fig. 3), these are of little clinical significance. The amount of calcium excreted in urine on each day did vary over the course of the study (study date[BDC to R+4]; F = 2.7, p < 0.0001) and the RVE and CTRL groups responded differently (study date[BDC to R+4] ×group; F= 1.4, p=0.028; Fig. 4). The CTRL group showed strong
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Fig. 2 Changes in markers of bone formation and resorption during and after bed rest in each subject group. a PINP (bone formation); b BAP (bone formation); c CTX (bone resorption); d TRACP 5b (osteoclastic turnover). Error bars represent standard error of the mean percentage difference to baseline (BDC-2) values. Time axis is
to scale up until R+7. Significance indicated by: a p<0.05; b p<0.01; c p<0.001. BR day of bed rest, R+ day of recovery. Note: R+1 blood drawing occurred prior to subjects re-ambulating, CTRL control group, RVE resistive vibration exercise group
increases in the amount of calcium excreted in the urine per day during bed rest whereas the RVE group showed little change. Interestingly, the excretion of calcium is already scaled back after 1 day of re-ambulation (on R+2).
DXA—bone mass
Fig. 3 Changes in intact PTH and serum calcium during and after bed rest in each subject group. a PTH; b serum calcium. Error bars represent standard error of the mean percentage difference to baseline (BDC-2) values. Time axis is to scale up until R+7. Significance
indicated by: a p<0.05; b p<0.01; c p<0.001. BR day of bed rest, R+ day of recovery. Note: R+1 blood drawing occurred prior to subjects re-ambulating, CTRL control group, RVE resistive vibration exercise group
Whole-body bone mass (sub-total, without head) changed in the bed-rest (study date[BDC to BR55]; F=4.7, p=0.0015)
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Fig. 4 Changes urinary calcium excretion during and after bed rest in each subject group. Values are mean (SEM) change in urinary calcium excretion (mmol per day) compared to baseline (BDC-2 and BDC-1 averaged) amount. Values with error bars at or above the lines indicated by a, b, and c have p values of <0.05, <0.01, or <0.001, respectively. BR day of bed rest, R+ day of recovery, CTRL control group, RVE resistive vibration exercise group
and recovery (study date[BR55 to R+360]; F=4.8, p=0.0007) phases of the study. Inspection of Table 4 suggests marginally lesser losses of bone in the RVE group, although there was no statistical evidence from ANOVA for a different response between the RVE and CTRL groups (group×study date; F both <0.3, p both >0.91). When the bone mass data was divided into arm, trunk, and leg sub-regions, the greatest, and statistically most significant, losses are seen in the legs of the CTRL group (Fig. 5; no significant changes in arm bone mass over the course of the study, data not shown). Whilst evidence existed for changes in bone mass during bed rest (study date[BDC to BR55]; F=2.8, p=0.025; study date[BDC to BR55] ×sub-region; F=1.3, p=0.25) and recovery (study date[BR55 to R+360]; F=2.1, p=0.061; study date[BR55 to R+360] ×sub-region; F=2.1, p=0.023), there was no evidence of a different response between the RVE and CTRL groups in any of the subregions (F all ≤0.95, p all ≥0.48). DXA—lean mass Changes in lean mass in the during both bed rest (study date[BDC to BR55]; F=1.7, p=0.14; study date[BDC to BR55] × sub-region; F = 11.9, p < 0.0001) and recovery (study date[BR55 to R+360]; F=2.2, p=0.058; study date[BR55 to R+360] × sub-region; F=10.9, p<0.0001) depended differed between the body sub-regions of arm, trunk, and leg. The countermeasure impacted upon these changes (group× study date[BDC to BR55]; F=2.1, p=0.086, group×study date[BDC to BR55] ×sub-region; F=2.6, p=0.0094; group× study date[BR55 to R + 360]; F=2.6, p=0.025; group×study date[BR55 to R + 360] ×sub-region; F=2.4, p=0.0093), with the CTRL group showing a strong reduction in leg lean
mass during bed rest, which is not seen in the RVE group (Fig. 5). Despite decreases in bone mass in the trunk, the CTRL group shows increased trunk lean mass during bed rest (from BR44; Fig. 5) and up to the final scanning session 1 year afterwards (R+360). The RVE group does not show these changes. Arm lean mass was increased in both the CTRL and RVE groups during bed rest and up to 28 days afterwards (data not shown).
Discussion This study has a number of interesting and novel results. Firstly, with respect to the effectiveness of the resistive vibration exercise countermeasure, the biochemical markers of bone metabolism showed increased bone formation due to exercise. The countermeasure restricted the increases in bone resorption seen in the CTRL group and consequently showed no changes in iPTH during bed rest. The control group showed a pattern of increased bone resorption, marginally (non-significant) decreased bone formation, and decreased iPTH levels. The decrease in iPTH is most likely due to a slight increase of serum calcium from bone resorption, which is recognized by the calcium sensors in the parathyroid gland to subsequently increase urinary calcium excretion [36–42] (as seen in the CTRL group of this study) and maintain calcium homeostasis in blood. Otherwise, the observed changes in serum calcium levels are statistically significant but of no clinical relevance. Increased osteoclast activity (TRACP 5b) was seen in both groups. Overall, it appears that the countermeasure exercise had its strongest effect on increasing bone formation, rather than limiting the increased bone resorption seen in the
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Fig. 5 Change in regional bone and lean mass in the leg and trunk as measured by DXA over the study period in each subject group. a Bone mass leg, b bone mass trunk, c lean mass leg, d lean mass trunk. Error bars represent standard error of the mean difference to baseline
(BDC-3 and BR2) values. Significance indicated by: a p<0.05; b p< 0.01, c p<0.001. CTRL inactive control group, RVE resistive vibration exercise group, BR day of bed rest, R+ day of recovery
inactive subjects. With respect to the whole-body composition data, analysis showed a trend that loss of leg and trunk bone mass was impeded in the countermeasure exercise group, although this effect was marginal statistically, and that the loss of lean mass in the leg was strongly reduced. We have identified two other studies which examined exercise countermeasures in prolonged bed rest with measures of bone metabolism and whole-body DXA [5, 23]. Some parameters (specifically leg bone mass and the bone formation marker, BAP) are comparable with the current work. In a longer (17-week) bed-rest study as in the current work, Shackelford and colleagues [5] observed a similar amount of leg bone mass loss in the inactive group (1.8% in both their and the current work), with a nonsignificant loss of 0.8% (compared to baseline) of leg bone mass in the group which performed resistive exercises. In the current work, the loss of leg bone mass in the RVE group equates to 0.67%. Further work is indeed necessary to differentiate any additive effects of whole-body vibration during resistive exercise. Interestingly, Shackelford and colleagues [5] did not find a significant ANOVA result for exercise group and study time in leg bone mass changes,
but observed significant decreases in leg bone mass in their control group, but not in their exercise group. This pattern is the same in our current work. It may be that whole-body DXA is not the most appropriate methodology for detecting regional changes in bone mass or density during bed rest and that other methodologies, such as quantitative computed tomography [4], may be more appropriate. Shackelford and colleagues [5] also report increased BAP levels in their resistive exercise group. We likewise noted this change in our RVE group. In contrast, Smith and colleagues [23] did not find any change in BAP in their lower body negative pressure exercise group. These differences may be understood in terms of the loading levels during exercise. Both in the current work and that of Shackelford and colleagues, high loads were achieved during exercise. During lower body negative pressure exercise, much lower forces are achieved (approximately 1 to 1.2 times body weight). It is well known that higher-than-normal loads are needed to stimulate bone formation [6], which is borne out by studies finding little positive impact of acute endurance exercise on bone turnover [43, 44], but an increase of bone formation relative to resorption after acute resistance exercise [45].
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Another interesting aspect of the findings of the current study was the speed with which bone metabolism was modulated with bed rest and re-ambulation and also the long-term changes in recovery. Zerwekh and colleagues [26] observed an increase in bone resorption serum markers within 1–4 weeks of bed rest. In contrast, a study of urine markers of bone resorption has reported an increase in bone resorption within 2 days of bed rest [46]. In our current data, increases in the bone resorption marker, CTX, were observed within 3 days of bed rest, reaching statistical significance at 3 days in the RVE group and 12 days in the CTRL group, respectively. Similarly, osteoclastic activity (TRACP 5b) was marginally increased within 5 days of bed rest and significantly so by 12 days in both groups. After bed rest, bone resorption (CTX; TRACP 5b) is scaled back within 3 days, but is still marginally increased at 7 days (CTX). These findings support the view of Baecker and co-workers [46] and also work from our group [47] that osteoclastic activity responds to un-loading and re-loading on a very short time scale. Reductions in iPTH were observed in the inactive (CTRL) group within 12 days of bed rest. Also, upon re-ambulation, iPTH returns to baseline levels in the CTRL group within 3 days of bed rest which fits well with data of urine excretion of calcium. Bone formation (PINP) is increased first 7 days after bed rest and the other bone formation marker (BAP) increased some time after the R+7 blood drawing (i.e., was increased at R+28) in the CTRL group. Taken together, the data of the current work suggest that a metabolic response of bone metabolism to extreme changes in activity levels (bed rest/ spaceflight) occur within 3 to 7 days. The findings of increased bone formation (PINP, BAP) long term after bed rest, with marginal increases in BAP present up to 180 days after bed rest and PINP increased up to 28 days of recovery, support the thesis that recovery of bone loss is a long-term ongoing process after spaceflight [48] and bed rest [47]. It is worthy to note that bone formation (PINP, BAP) appeared to be decreased during bed rest (control group), although the effect is marginal statistically. Some authors concluded that bone formation does not decrease during bed rest and that loss of bone is driven by increased bone resorption [5, 21, 49], although other authors have suggested that bone formation does indeed reduce in spaceflight and/or simulation [20, 36, 39, 50–52]. In our current work, we had multiple blood drawings, which may be the reason why it is possible to observe a subtle decrease. These findings add weight to the argument that reduced bone formation may contribute to the bone loss observed in bed rest, immobilization, and spaceflight. In conclusion, the current work found a resistive vibration exercise countermeasure impeded loss of bone and muscle during 8 weeks of bed rest. Changes in biochemical markers of bone metabolism were also
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impeded, with the exercise group showing increased bone formation and less increases in bone resorption. These findings were in stark contrast to the inactive subjects, who showed very subtle decreases in bone formation and stronger increases in bone resorption. The findings of the current study suggest that recovery of bone after prolonged bed rest is a long-term process, requiring at least 180 days before measurable losses in bone mass are reversed. The metabolic signs of increased bone turnover persist beyond 180 days after bed rest and further work is required to examine when this process is completed. Finally, the findings of the current study suggest that reactions of biochemical markers of bone metabolism to extreme changes in activity (bed rest/re-ambulation) occur within 3–7 days. Acknowledgements The authors wish to thank the subjects who participated in the study and the staff of ward 18A at the Charité Campus Benjamin Franklin Hospital, Berlin, Germany. The Berlin Bed-Rest Study was supported by grant 14431/02/NL/SH2 from the European Space Agency. The investigations in the current study were supported by grant 50WB0522 from the Deutschen Zentrum für Luftund Raumfahrt (German Aerospace Center). The Berlin Bed-Rest Study was also sponsored by the Charité Campus Benjamin Franklin, MSD Sharp & Dohme, Lilly Germany, Novartis, Servier Germany, P&G, Wyeth, Siemens, and Seca. Daniel L. Belavý was supported by a post-doctoral fellowship from the Alexander von Humboldt Foundation. Conflicts of interest Dieter Felsenberg and Jörn Rittweger are acting as consultants to the European Space Agency and Novotec Medical for the exploitation of this study’s results. All other authors have no conflicts of interest.
References 1. Oganov VS, Grigoriev AI, Voronin LI et al (1992) Bone mineral density in cosmonauts after 4.5–6 month long flights aboard orbital station MIR. Aerospace Environ Med 26:20–24 2. Le Blanc A, Schneider V, Shackelford L et al (2000) Bone mineral and lean tissue loss after long duration space flight. J Musculoskelet Neuronal Interact 1:157–160 3. Le Blanc A, Lin C, Shackelford L et al (2000) Muscle volume, MRI relaxation times (T2), and body composition after spaceflight. J Appl Physiol 89:2158–2164 4. Rittweger J, Frost HM, Schiessl H et al (2005) Muscle atrophy and bone loss after 90 days' bed rest and the effects of flywheel resistive exercise and pamidronate: results from the LTBR study. Bone 36:1019–1029 5. Shackelford LC, LeBlanc AD, Driscoll TB et al (2004) Resistance exercise as a countermeasure to disuse-induced bone loss. J Appl Physiol 97:119–129 6. Frost HM (2001) From Wolff’s law to the Utah paradigm: insights about bone physiology and its clinical applications. Anat Rec 262:398–419 7. Tesch PA, Buchanan P, Dudley GA (1990) An approach to counteracting long-term microgravity-induced muscle atrophy. Physiologist 33:S77–S79
606 8. Greenleaf JE, Bulbulian R, Bernauer EM et al (1989) Exercisetraining protocols for astronauts in microgravity. J Appl Physiol 67:2191–2204 9. Convertino VA (1991) Neuromuscular aspects in development of exercise countermeasures. Physiologist 34:S125–128 10. Cardinale M, Bosco C (2003) The use of vibration as an exercise intervention. Exerc Sport Sci Rev 31:3–7 11. Torvinen S, Sievanen H, Jarvinen TAH et al (2002) Effect of 4min vertical whole body vibration on muscle performance and body balance: a randomized cross-over study. Int J Sports Med 23:374–379 12. Fontana TL, Richardson CA, Stanton WR (2005) The effect of weight-bearing exercise with low frequency, whole body vibration on lumbosacral proprioception: a pilot study on normal subjects. Aust J Physiother 51:259–263 13. Delecluse C, Roelants M, Verschueren S (2003) Strength increase after whole-body vibration compared with resistance training. Med Sci Sports Exerc 35:1033–1041 14. Issurin VB, Liebermann DG, Tenenbaum G (1994) Effect of vibratory stimulation training on maximal force and flexibility. J Sports Sci 12:561–566 15. Torvinen S, Kannus P, Sievanen H et al (2002) Effect of fourmonth vertical whole body vibration on performance and balance. Med Sci Sports Exerc 34:1523–1528 16. Ribot-Ciscar E, Butler JE, Thomas CK (2003) Facilitation of triceps brachii muscle contraction by tendon vibration after chronic cervical spinal cord injury. J Appl Physiol 94:2358–2367 17. Roll JP, Vedel JP, Ribot E (1989) Alteration of proprioceptive messages induced by tendon vibration in man: a microneurographic study. Exp Brain Res 76:213–222 18. Kiiski J, Heinonen A, Jarvinen TL et al (2008) Transmission of vertical whole body vibration to the human body. J Bone Miner Res 23:1318–1325 19. Rubin C, Pope M, Fritton JC et al (2003) Transmissibility of 15hertz to 35-hertz vibrations to the human hip and lumbar spine: determining the physiologic feasibility of delivering low-level anabolic mechanical stimuli to skeletal regions at greatest risk of fracture because of o. Spine 28:2621–2627 20. Le Blanc A, Schneider V, Spector E et al (1995) Calcium absorption, endogenous secretion and endocrine changes during and after long-term bed rest. Bone 16:301S–304S 21. Le Blanc AD, Driscol TB, Shackelford LC et al (2002) Alendronate as an effective countermeasure to disuse induced bone loss. J Musculoskel Neuron Interact 2:335–343 22. Miyamoto A, Shigematsu T, Fukunaga T et al (1998) Medical baseline data collection on bone and muscle change with space flight. Bone 22:79S–82S 23. Smith SM, Davis-Street JE, Fesperman JV et al (2003) Evaluation of treadmill exercise in a lower body negative pressure chamber as a countermeasure for weightlessness-induced bone loss: a bed rest study with identical twins. J Bone Miner Res 18:2223–2230 24. Smith SM, Wastney ME, O’Brien KO et al (2005) Bone markers, calcium metabolism, and calcium kinetics during extended duration space flight on the Mir space station. J Bone Miner Res 20:208–218 25. Van der Wiel HE, Lips P, Nauta J et al (1993) Intranasal calcitonin suppresses increased bone resorption during short-term immobilization: a double-blind study of the effects of intranasal calcitonin on biochemical parameters of bone turnover. J Bone Miner Res 8:1459–1465 26. Zerwekh JE, Ruml LA, Gottschalk F et al (1998) The effects of twelve weeks of bed rest on bone histology, biochemical markers of bone turnover, and calcium homeostasis in eleven normal subjects. J Bone Miner Res 13:1594–1601 27. Rittweger J, Belavy DL, Hunek P et al (2006) The Berlin BedRest Study: maintenance of a highly demanding resistive vibration
Osteoporos Int (2010) 21:597–607
28.
29.
30.
31.
32.
33.
34.
35. 36.
37.
38.
39. 40.
41.
42.
43.
44.
45.
46.
47.
exercise program during 56 days of strict bed-rest. Int J Sport Med 27:553–559 Blottner D, Salanova M, Puttmann B et al (2006) Human skeletal muscle structure and function preserved by vibration muscle exercise following 55 days of bed rest. Eur J Appl Physiol 97:261–271 Gabriel DA, Kamen G, Frost G (2006) Neural adaptations to resistive exercise: mechanisms and recommendations for training practices. Sports Med 36:133–149 Nishizawa Y, Nakamura T, Ohta H et al (2005) Guidelines for the use of biochemical markers of bone turnover in osteoporosis (2004). J Bone Miner Metab 23:97–104 Mulder ER, Gerrits KH, Kleine BU et al (2007) High-density surface EMG study on the time course of central nervous and peripheral neuromuscular changes during 8weeks of bed rest with or without resistive vibration exercise. J Electromyogr Kinesiol: . doi:10.1016/j.jelekin.2007.1004.1002 Mulder ER, Stegeman DF, Gerrits KH et al (2006) Strength, size and activation of knee extensors followed during 8 weeks of horizontal bed rest and the influence of a countermeasure. Eur J Appl Physiol 97:706–715 Belavý DL, Richardson CA, Wilson SJ et al (2007) Superficial lumbo-pelvic muscle overactivity and decreased co-contraction after 8 weeks of bed rest. Spine 32:E23–29 Belavý DL, Richardson CA, Wilson SJ et al (2007) Tonic to phasic shift of lumbo-pelvic muscle activity during 8 weeks of bed rest and 6-months follow-up. J Appl Physiol 103:48–54 Pinheiro JC, Bates DM (2000) Mixed-effects models in S and SPLUS. Springer, Berlin Arnaud SB, Sherrard DJ, Maloney N et al (1992) Effects of 1week head-down tilt bed rest on bone formation and the calcium endocrine system. Aviat Space Environ Med 63:14–20 Brown EM, Gamba G, Riccardi D et al (1993) Cloning and characterization of an extracellular Ca(2+)-sensing receptor from bovine parathyroid. Nature 366:575–580 Morey-Holton ER, Whalen RT, Arnaud SB et al (1983) The skeleton and its adaptation to gravity. In: Fregly MJ, Blatteis CM (eds) Handbook of physiology—environmental physiology. Oxford University Press, New York, pp 691–719 Holick MF (1998) Perspective on the impact of weightlessness on calcium and bone metabolism. Bone 22:105S–111S Hughes-Fulford M (1993) Review of the biological effects of weightlessness on the human endocrine system. Receptor 3:145– 154 Morey-Holton ER, Schnoes HK, DeLuca HF et al (1988) Vitamin D metabolites and bioactive parathyroid hormone levels during Spacelab 2. Aviat Space Environ Med 59:1038–1041 Vico L, Lafage-Proust MH, Alexandre C (1998) Effects of gravitational changes on the bone system in vitro and in vivo. Bone 22:95S–100S Herrmann M, Muller M, Scharhag J et al (2007) The effect of endurance exercise-induced lactacidosis on biochemical markers of bone turnover. Clin Chem Lab Med 45:1381–1389 Guillemant J, Accarie C, Peres G et al (2004) Acute effects of an oral calcium load on markers of bone metabolism during endurance cycling exercise in male athletes. Calcif Tissue Int 74:407–414 Whipple TJ, Le BH, Demers LM et al (2004) Acute effects of moderate intensity resistance exercise on bone cell activity. Int J Sports Med 25:496–501 Baecker N, Tomic A, Mika C et al (2003) Bone resorption is induced on the second day of bed rest: results of a controlled crossover trial. J Appl Physiol 95:977–982 Rittweger J, Felsenberg D (2009) Recovery of muscle atrophy and bone loss from 90 days bed rest: results from a one-year followup. Bone 44:214–224
Osteoporos Int (2010) 21:597–607 48. Sibonga JD, Evans HJ, Sung HG et al (2007) Recovery of spaceflight-induced bone loss: bone mineral density after longduration missions as fitted with an exponential function. Bone 41:973–978 49. Smith SM, Wastney ME, Morukov BV et al (1999) Calcium metabolism before, during, and after a 3-mo spaceflight: kinetic and biochemical changes. Am J Physiol Regulatory Integrative Comp Physiol 277:1–10
607 50. Donaldson CL, Hulley SB, Vogel JM et al (1970) Effect of prolonged bed rest on bone mineral. Metabolism 19:1071–1084 51. Le Blanc AD, Schneider VS, Evans HJ et al (1990) Bone mineral loss and recovery after 17 weeks of bed rest. J Bone Miner Res 5:843–850 52. Lueken SA, Arnaud SB, Taylor AK et al (1993) Changes in markers of bone formation and resorption in a bed rest model of weightlessness. J Bone Miner Res 8:1433–1438
