Krebs von den Lungen-6 levels at admission predicts exercise-induced hypoxemia before and after discharge in patients with COVID-19

BACKGROUND

There are no reports of exercise-induced hypoxemia in patients with coronavirus disease 2019 (COVID-19). Additionally, the predictive factors and prevalence of exercise-induced hypoxemia are unknown. This study investigated the incidence and predictive factors of exercise-induced hypoxemia before and after discharge in patients with COVID-19.

METHODS

We enrolled 77 patients diagnosed with COVID-19 who were hospitalized between November 2020 and October 2021 and who underwent a 6-min walk test before and after discharge. Based on the test results, we classified patients into exercise-induced and non-exercise-induced hypoxemia groups and investigated the predictive factors of exercise-induced hypoxemia using logistic regression analysis.

RESULTS

The incidences of exercise-induced hypoxemia in patients with COVID-19 were 37.7% and 19.5% before and after discharge, respectively. At admission, the Krebs von den Lungen-6 levels was the associated factor for exercise-induced hypoxemia in patients with COVID-19 before and after discharge, with cut-off values of 314 U/mL and 367 U/mL, respectively. Age and lactate dehydrogenase levels were the associated factors for exercise-induced hypoxemia in patients with COVID-19 before discharge, with cut-off values of 61 years and 492 U/L, respectively.

CONCLUSIONS

Some patients with COVID-19 may continue to experience exercise-induced hypoxemia after discharge. Age, lactate dehydrogenase, and Krebs von den Lungen-6 levels at admission could serve as predictive markers of exercise-induced hypoxemia before and after discharge in these patients.

Efficacy of exercise training-based cardiac rehabilitation programmes after transcatheter aortic valve implantation: A systematic review and meta-analysis

Background

The beneficial effects of exercise training-based cardiac rehabilitation (CR) in different cardiac conditions have been previously studied. In this meta-analysis, we focused on the potential impact of CR on patients undergoing transcatheter aortic valve implantation (TAVI).

Methods

Multiple databases were searched in a systematic approach to find the eligible studies. All the studies investigating the potential impact of exercise training-based CR programmes on exercise capacity and health-related quality of life in patients undergoing TAVI were retrieved. The primary endpoint of interest was 6-min walk test (6MWT). The pooled standardized mean difference (SMD) and 95 % confidence interval (CI) were measured to compare the improvement or worsening the endpoints using a random- or fixed-effects model, as appropriate.

Results

A total of eleven studies (685 patients) were considered eligible for quantitative synthesis. The results showed that performing exercise training-based CR after TAVI is associated with significant improvement in 6MWT (SMD 0.59, 95 % CI (0.48; 0.71), p < 0.01), Barthel index (SMD 0.73, 95 % CI (0.57; 0.89), p < 0.01), 12-item Short Form (SF-12) physical (SMD 0.30, 95 % CI (0.08; 0.52), p < 0.01) and mental (SMD 0.27, 95 % CI (0.05; 0.49), p = 0.02) survey scores, and hospital anxiety and depression scale - depression (HADS-D) score (SMD -0.26, 95 % CI (-0.42; -0.10), p < 0.01).

Conclusion

Performing exercise training-based CR following TAVI has significant benefits regarding physical capacity and health-related quality of life irrespective of the programme duration.

Preoperative 6-minute walk distance is associated with postoperative complications in patients undergoing laparoscopic gastrointestinal cancer surgery

OBJECTIVE

The 6-min walk test (6MWT) is a simple and valid method to evaluate cardiopulmonary function. We performed this prospective study in patients undergoing laparoscopic gastrointestinal cancer surgery to explore the association between preoperative 6MWT performance and overall postoperative complications.

METHODS

This study was registered at clinicaltrials.gov (NCT03711526). The study consecutively enrolled patients receiving laparoscopic gastrointestinal cancer surgery in our institution. All patients performed the 6MWT upon recruitment and received 30 days of postoperative follow-up. The primary outcome was overall complications, defined by ≥ grade I Clavien-Dindo (CD) classification (2004) complications. Multivariable logistic regression was used to test the association of 6-min walk distance (6MWD) with the outcome.

RESULTS

A total of 184 patients were included in the final analyses. In the 37 (20.1 %) patients with overall complications, the mean (standard deviation) preoperative 6MWD was 469.1 (86.8) m. In patients with no complications, the 6MWD was 502.6 (90.2) m. The mean difference was 33.5 m (95 % confidence interval, 1.3, 65.7; P = 0.042). A longer preoperative 6MWD was associated with a lower odds of developing postoperative complications (odds ratio, 0.994 per meter increase; 95 % confidence interval, 0.989, 0.999; p = 0.023).

CONCLUSION

This study indicated an association between the preoperative 6MWD and postoperative complications in patients undergoing laparoscopic gastrointestinal cancer surgery.

Bicycle ergometer exercise during hemodialysis and its impact on quality of life, aerobic fitness and dialysis adequacy: A pilot study

BACKGROUND

Chronic kidney disease patients on hemodialysis commonly have a worse quality of life (QoL) due to complications of the disease and dialysis procedure. Physical exercise has emerged as a strategy to improve this scenario. The objective of this study was to evaluate the effect of an intradialytic aerobic exercise program on QoL and aerobic fitness in hemodialysis patients.

MATERIAL AND METHODS

These are a secondary analysis of clinical trial data previously published in which hemodialysis patients were randomized into "bike group" (using an adapted exercise bicycle) or "control group" (usual care). The exercise sessions lasted 45 min (5 min of warm-up, 35 min of moderate-intensity and 5 min of cool-down) three times/week for three months. The QoL domains were assessed using the SF-36 QoL questionnaire. Aerobic fitness was evaluated using the 6-min walk test (6MWT). Circulating cytokines, biochemical parameters and Kt/V were also assessed.

RESULTS

Nine patients completed three months of exercise (5 men, 44 ± 11 years), and nine were in the control group (6 men, 44 ± 14 years). In the bike group, there was a trend to improve the physical role domain (p = 0.06) regarding QoL, an improvement in the 6MWT (p = 0.02), and in the Kt/V (p = 0.03) after three months. There was a positive correlation between the general health domain and Kt/V (r = 0.691; p = 0.003) and an inverse correlation between the physical functioning domain and plasma TNF-α levels (r = -0.514; p = 0.04).

CONCLUSIONS

12 weeks of intradialytic aerobic exercise was enough to benefit hemodialysis patients' quality of life, aerobic fitness, and quality of dialysis.

CLINICALTRIALS

gov id: NCT04375553.

Pulmonary Rehabilitation in Noncystic Fibrosis Bronchiectasis

BACKGROUND

Current guidelines for the treatment of noncystic fibrosis bronchiectasis (NCFB) recommend pulmonary rehabilitation (PR), but to date, there are few studies that have proven its effectiveness.

OBJECTIVE

The main objective of this study was to examine the effect of PR on pulmonary function tests and exercise capacity.

METHOD

The aim of this study was to systematically review the effects of PR in NCFB on (1) forced expiratory volume in the first second (FEV1) and (2) exercise capacity evaluated by the 6-min walk test (6MWT) and the incremental shuttle walk test (ISWT). This meta-analysis was undertaken according to PRISMA recommendations.

RESULTS

This pair-wise meta-analysis included data obtained from studies that enrolled 529 NCFB patients. The FEV1 assessment after PR between the active and control group did not show any significant increase (FEV1 difference 0.084 mL; CI: -0.064, +0.233; p = 0.264), and there was an increasing trend (188 mL; CI: -0 to 0.009, +0.384) at the limits of statistical significance (p = 0.061). Walked distance showed a significant increase in the PR group compared to the control group (ISWT distance difference 070.0 m; CI: 55.2, 84.8; p < 0.001), and this finding was confirmed before and after PR both by the ISWT (68.85 m greater than baseline; CI: 40.52, 97.18; p < 0.001) and by the 6MWT (37.7 m greater than baseline; CI: 20.22, 55.25; p < 0.001).

CONCLUSIONS

PR improves exercise tolerance in NCFB patients, but it has a modest impact on respiratory function.

Correlation between functional capacity and oxidative stress and inflammation in hemodialysis patients

INTRODUCTION

Patients with chronic kidney disease (CKD) may present impaired functional capacity due to peripheral muscle involvement. Oxidative stress and inflammation are probably involved in this pathophysiology. This study aimed to evaluate the association between functional capacity and biomarkers of oxidative stress as well as biomarkers of inflammation in patients under chronic hemodialysis therapy.

METHOD

Cross-sectional study including 41 patients from a single hemodialysis center. Functional capacity was assessed through the 6-min walk test (6MWT). The assessed blood biomarkers were: malondialdehyde (MDA) (oxidative stress, TBARS method) and angiopoietin-2 (Ang-2) (inflammation, ELISA). The influence of gender on impairment of functional capacity was further explored.

RESULTS

There was an inversely proportional correlation between the 6MWD and MDA (r = -,322 and p = 0.040) and Ang-2 (r = -, 376 and p = 0.016) values. 6MWD was 370.9 ± 101.2 m and 391.4 ± 108.2 m in women and men, respectively (p < 0.001), which means 29.3% and 34.3% reduction of the expected values for healthy individuals from the same age range.

CONCLUSION

Patients with CKD under hemodialysis, regardless of gender, presented impaired performance in 6MWT and this impairment was associated with oxidative stress and inflammation.

The 6-min walk test in the functional evaluation of patients with lung cancer qualified for lobectomy

OBJECTIVES

The American College of Chest Physicians guidelines recommend low-technology exercise tests in the functional evaluation of patients with lung cancer considered for resectional surgery. However, the 6-min walk test (6MWT) is not included, because the data on its clinical value are inconsistent. Our goal was to evaluate the 6MWT in assessing the risk of cardiopulmonary complications in candidates for lung resection.

METHODS

We performed a retrospective assessment of clinical data and pulmonary function test results in 947 patients, mean age 65.3 (standard deviation 9.5) years, who underwent a single lobectomy for lung cancer. In 555 patients with predicted postoperative values ≤60%, the 6MWT was performed. The 6-min walking distance (6MWD) and the distance-saturation product (DSP), which is the product of the 6MWD in metres, and the lowest oxygen saturation registered during the test were assessed.

RESULTS

A total of 363 patients with predicted postoperative values <60% and a 6MWT distance (6MWD) ≥400 m or DSP ≥ 350 m% had a lower rate of cardiopulmonary complications than patients with shorter 6MWD or lower DSP values [odds ratio (OR) 0.53, 95% confidence interval (CI) 0.35-0.81] and 0.47 (95% CI 0.30-0.73), respectively. This result was also true for patients with predicted postoperative values <40%, ORs 0.33 (95% CI 0.14-0.79) and 0.25 (95% CI 0.10-0.61), respectively.

CONCLUSIONS

The 6MWT is useful in the assessment of operative risk in patients undergoing a single lobectomy for lung cancer. It helps to stratify the operative risk, which is lower in patients with 6MWD ≥400 m or DSP ≥350 m% than in patients with a shorter 6MWD or lower DSP values.

Shorter corridors can be used for the six-minute walk test in subjects with chronic lung diseases

BACKGROUND

The main limitation of the six-minute walk test (6-MWT) is that not all pulmonary function testing facilities have an indoor flat, 30-m-long corridor. Therefore, this study aimed 1) to evaluate the correlation and agreement of the distances walked in 30-m- vs. 15-m-long corridors by subjects with chronic lung diseases (CLD group) and 2) to compare the levels of oxygen saturation (nSpO₂), blood pressure (BP), heart rate recovery at minute one post-exercise (HRR1), and Borg scale scores for dyspnea and fatigue between the two distances walked.

METHODS

A prospective, cross-sectional study was conducted at the National Institute of Respiratory Diseases in Mexico City. Subjects with chronic lung diseases and healthy adults were invited to participate. The distance of the 6-MWT was randomly assigned based on whether the first test was in the 15-m or 30-m corridor.

RESULTS

Ninety individuals were included; the correlation in meters walked between the two corridors was r = 0.96 in CLD; the 95% limits of agreement for the 6-MWT ranged from -73 to +37 m. Most subjects walked further in the 30-m corridor (82%); however, the percent predicted values for the CLD group were 3.5% lower for the 15-m corridor than the 30-m corridor. Only 10.5% of the subjects with CLD would have been falsely classified as having a normal 6-MWT (false negative). No significant differences in the nSpO2, Borg scale, BP or HRR1 were found between the two 6-MWT corridor lengths.

CONCLUSION

The 6-MWT can be performed using a 15-m corridor in subjects with CLD, and the results for the distance walked, HRR1, nSpO₂, and Borg scale scores are similar to between the 15-m and 30-m corridors.

Agreement between Cardiopulmonary Exercise Test and Modified 6-Min Walk Test in Determining Oxygen Uptake in COPD Patients with Different Severity Stages

BACKGROUND

In moderate-to-severe chronic obstructive pulmonary disease (COPD) patients the 6-min walk test (6MWT) is often exhaustive and correlates with the incremental cycle cardiopulmonary exercise test (CPET).

OBJECTIVES

The aim of this study was to assess the agreement between oxygen uptake (VO2) measured during the 6MWT by portable equipment and incremental cycle exercise in COPD patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) I-IV.

METHODS

A total of 30 patients with COPD GOLD I-IV (14 patients GOLD stage I and II and 16 patients GOLD stage III and IV) underwent a 6MWT and an incremental CPET. Breath-by-breath analysis for VO2, carbon dioxide output (VCO2), and minute ventilation (VE) were measured during each test. Blood gas analysis and lactate measurements were performed before, during, and after the test.

RESULTS

VO2 in COPD patients GOLD stage I and II was 16.2 ± 4.2 mL/kg/min measured by 6MWT and 20.5 ± 7.0 mL/kg/min measured by CPET as compared to GOLD stage III and IV (11.2 ± 3.7 mL/kg/min measured by 6MWT and 15.5 ± 4.3 mL/kg/min measured by CPET). No significant correlation in VO2 measurements could be found between both tests in COPD GOLD I and II (r = 0.17), whereas the VO2 significantly correlated in patients with COPD stage III and IV (r = 0.7).

CONCLUSIONS

A significant relationship between VO2 measured by 6MWT and CPET could only be found in patients with more severe COPD but not in milder stages. 6MWT and CPET provide different VO2 measurements in COPD patients. The two methods cannot be used interchangeably.

Latent process model of the 6-minute walk test in Duchenne muscular dystrophy : A Bayesian approach to quantifying rare disease progression

Duchenne muscular dystrophy (DMD) is a rare X-linked genetic pediatric disease characterized by a lack of functional dystrophin production in the body, resulting in muscle deterioration. Lower body muscle weakness progresses to non-ambulation typically by early teenage years, followed by upper body muscle deterioration and ultimately death by the late twenties. The objective of this study was to enhance the quantitative understanding of DMD disease progression through nonlinear mixed effects modeling of the population mean and variability of the 6-min walk test (6MWT) clinical endpoint. An indirect response model with a latent process was fit to digitized literature data using full Bayesian estimation. The modeling data set consisted of 22 healthy controls and 218 DMD patients from one interventional and four observational trials. The model reasonably described the central tendency and population variability of the 6MWT in healthy subjects and DMD patients. An exploratory categorical covariate analysis indicated that there was no apparent effect of corticosteroid administration on DMD disease progression. The population predicted 6MWT began to rise at 1.32 years of age, plateauing at 654 meters (m) at 17.2 years of age for the healthy population. The DMD trajectory reached a maximum of 411 m at 8.90 years before declining and falling below 1 m at age 18.0. The model has potential to be used as a Bayesian estimation and posterior simulation tool to make informed model-based drug development decisions that incorporate prior knowledge with new data.

Long-Term Trends in Respiratory Function After Esophagectomy for Esophageal Cancer

BACKGROUND

Esophagectomy for esophageal cancer is known to lead to deterioration in respiratory function (RF). The aim of this study was to assess long-term trends in RF after esophagectomy and the impact of different operative procedures.

METHODS

A total of 52 patients with thoracic esophageal cancer who were scheduled for esophagectomy from 2003 to 2012 were enrolled. We prospectively evaluated patients for vital capacity (VC), forced expiratory volume in 1 s (FEV1.0), and 6-min walk distance (6MWD) before and after esophagectomy at 3, 6, 12, 24, and 60 mo.

RESULTS

Patients had mostly recovered their VC and FEV1.0 after 12 mo. After that point, VC and FEV1.0 declined again, reaching levels lower than baseline at 60 mo, with a median change ratio of 0.85 and 0.86, respectively. Although the 6MWD after open esophagectomy declined, patients treated with transhiatal esophagectomy and minimally invasive esophagectomy maintained above baseline levels throughout the follow-up period. Furthermore, we identified transhiatal esophagectomy (odds ratio [OR] = 0.03, 95% confidence interval [CI] 0.002-0.43, P = 0.01) and minimally invasive esophagectomy (OR = 0.14, 95% CI 0.02-0.94, P = 0.04) as favorable factors and postoperative pulmonary complication (OR = 9.14, 95% CI 1.22-68.6, P = 0.03) as an unfavorable factor for RF after 12 mo. Operative procedures had no significant impact on RF after 60 mo.

CONCLUSIONS

Our results support the notion that RF does not recover to the baseline level, and operative procedures have no significant impact on RF at late phase after esophagectomy.

Effects of the applied ancient boxing exercise on leg strength and quality of life in patients with osteoarthritis

This study aimed to investigate the effect of ancient boxing exercise on the strength of leg muscles and quality of life in patients with osteoarthritis. The subjects were divided into 2 groups, control group (CG) and experimental group (EG). The average aged of control and experimental group were 60.3±6.8 and 59.0±7.8 years, respectively. All volunteers were interviewed for basic information, evaluation of the criteria of research and sign consent to participate in the research. The outcome measurement consisted of five time sit to stand test, 6-min walk test, flexibility by sit and reach test, Berg Balance Scale, Timed Up and Go Test, knee injury and osteoarthritis outcomes score (KOOS) and quality of life of World Health Organization Thai brief version (WHOQOL-BERF-THAI). Prior and posttest measurements were performed at 0, 4, 8, and 12 weeks, and those who received ancient boxing exercise were given 60 min 3 times per week for 12 weeks. The results of the study showed that postexercise leg muscle strength, physical performances, quality of life and KOOS increased significantly after exercise. In conclusion, the ancient boxing exercise could increase the strength of leg muscles physical performances, quality of life in people with knee osteoarthritis. This exercise can be used as a long lasting exercise in the future.

Reference equations for the 6-minute walk distance in healthy Portuguese subjects 18-70 years old

INTRODUCTION

Six-minute walk test (6MWT) is used for evaluating functional exercise capacity. To the best of our knowledge, there are no reference equations to predict six-minute walk distance (6MWD) for the Portuguese population. The aims of the present study were to measure anthropometric data and 6MWD in a sample of healthy Portuguese population, to establish reference equations to predict 6MWD and to compare our equations with those obtained by previously published studies.

METHODS

We conducted an observational prospective study. We consecutively recruited 158 healthy 18-70 years old subjects from Porto district, who performed two 6MWTs using a standardized protocol. The best 6MWD was used for further analysis.

RESULTS

The mean 6MWD was 627.8m (SD=73.3m). The variables that were significantly associated with the 6MWD were age, sex, BMI and ΔHR (Heart Rate_{at the end of the test}-HR_{at rest)}. We found three explanatory models for 6MWD, the best with an explanatory power of 38%: 6MWD=721.7-1.6×Age-4.0×BMI+0.9×ΔHR+58.4×Sex. We verified that 6MWD decreased 1.6m per year of age, and 4.0m per unit of BMI and increased 0.892m per beat per minute. Moreover, on average, males walk 58.4m more than females (p<0.001). Applying equations from other studies to our population resulted in an overestimation or underestimation of the 6MWD.

CONCLUSION

The present study was the first to describe the 6MWD in healthy Portuguese people aged 18-70 years old and to propose predictive equations. These can contribute to improving the evaluation of Caucasian Mediterranean patients with diseases that affect their functional capacity.

Long-term effects of device-guided slow breathing in stable heart failure patients with reduced ejection fraction

Background

Slow breathing (SLOWB) alleviates symptoms of chronic heart failure (HF) but its long-term effects are unknown. We examined the acute and long-term impact of device-guided breathing on hemodynamics and prognostic parameters in HF patients with reduced ejection fraction (HFrEF).

Methods and results

Twenty-one patients with HFrEF (23.9 ± 5.8%, SD ± mean) on optimal medical therapy underwent blood pressure (BP), heart rate (HR), HR variability, 6-min walk test (6MWT), cardiopulmonary exercise testing (CPET), and echocardiography measurements before and 3 months after SLOWB home training (30 min daily). After 3 months, all patients were assigned to continue SLOWB (Group 1) or no-SLOWB (Group 2). All tests were repeated after 6 months. Acute SLOWB (18 ± 5 vs 8 ± 2 breaths/min, P < 0.001) had no influence on BP and HR but improved saturation (97 ± 2 vs 98 ± 2%, P = 0.01). Long-term SLOWB reduced office systolic BP (P < 0.001) but not central or ambulatory systolic BP. SLOWB reduced SDNN/RMSSD ratio (P < 0.05) after 3 months. One-way repeated measures of ANOVA revealed a significant increase in 6MWT and peak RER (respiratory exchange ratio) from baseline to 6-month follow-up in group 1 (P < 0.05) but not group 2 (P = 0.85 for 6MWT, P = 0.69 for RER). No significant changes in echocardiography were noted at follow-up. No HF worsening, rehospitalisation or death occurred in group 1 out to 6-month follow-up. Two hospitalizations for HF decompensation and two deaths ensued in group 2 between 3- and 6-month follow-up.

Conclusions

SLOWB training improves cardiorespiratory capacity and appears to slow the progression of HFrEF. Further long-term outcome studies are required to confirm the benefits of paced breathing in HFrEF.

Albuterol as an adjunctive treatment to enzyme replacement therapy in infantile-onset Pompe disease

BACKGROUND

Early initiation of enzyme replacement therapy (ERT) with recombinant human acid alpha-glucosidase is an effective treatment for patients with infantile-onset Pompe disease (IOPD) but cannot prevent a slow progression of myopathy. Albuterol has been shown to be helpful in adult patients with Pompe disease, and therefore, we administered an open-label adjunctive therapy with albuterol in IOPD patients undergoing ERT.

METHODS

Fourteen patients, aged 2 to 12 years, were enrolled in this study; all of them had a disease onset before 12 months of life, and 13 of them were ambulatory because of early initiation of ERT. All patients received albuterol (also referred to as salbutamol) 12 mg daily for 26 weeks. The outcome measurements included a 6-minute walk test, four-stair climb test (SCT), the standing/walking/running/jumping domains of Gross Motor Function Measure-88, speech quality, serum creatine kinase, and urinary glucose tetrasaccharide. Outcome and safety measurements were evaluated at baseline, and at 1, 3, and 6 months (26 weeks) after entering the trial.

RESULTS

After a period of 26 weeks, among the 12 patients who were able to complete the SCT, the median time needed decreased by 22% (p = 0.034). Other parameters inconsistently improved in a variety of individuals. Eleven adverse events, including nausea, urinary frequency, and tachycardia, were potentially related to the study drug, but all were mild and disappeared after a brief drug withdrawal. One patient was actively withdrawn from the trial because of poor compliance.

CONCLUSIONS

The results of our study suggest that albuterol showed a good safety profile as an adjunctive treatment in our IOPD cohort, although the benefits are limited.

Effect of the 6-minute walk test on plantar loading and capability to produce ankle plantar flexion forces

The six-minute walk test (6MWT) is used to evaluate the ambulatory capacity of patients suffering from respiratory disorders, obesity or neuromuscular diseases. Our primary aim was to evaluate the effects of the 6MWT on the postural sway and the ankle plantar flexion forces in healthy subjects. We measured the ankle plantar flexion forces and the plantar contact area before and after a 6MWT in normal weight and overweight subjects with no history of respiratory, cardiac, and neuromuscular disorders. A post-6MWT sensation of bodily fatigue was evaluated by Multidimensional Fatigue Inventory (MFI) and Pichot fatigue scales. A computerized pedobarographic platform was used to collect the mean plantar contact area, the changes of the center of pressure (CoP) surface and its medial and lateral deviations. In a limited number of subjects, the reproducibility of all the measurements was explored. In both groups, the 6MWT elicited a sensation of bodily fatigue. It also significantly reduced the ankle plantar flexion forces, and increased both the mean plantar contact area and the CoP surface, the changes being not apparent after 10min. The post-6MWT lateral CoP deviations were accentuated in normal weight subjects, while an increase in medial CoP deviations occurred in overweight ones. The 6MWT-induced changes in the plantar flexion force and pedobarographic variables were reproducible. Because this study clearly showed some post-6MWT alterations of the subjects' posture sway of our subjects, we questioned the possible mechanisms occurring that could explain the altered muscle force and the transient destabilization of posture after the 6MWT.