Abstract
Background
In patients with chronic pain, aerobic deconditioning can explain part of observed disability and disadvantage. The objective of the present study was to assess the change in VO 2 max after a four-week exercise rehabilitation programme in this population.
Methods
In a prospective study, 121 patients underwent a cycle ergometer exercise tolerance test with VO 2 max measurement before and after a four-week exercise rehabilitation programme (which included aerobic training, muscle strengthening, occupational therapy and stretching).
Results
We observed a statistically significant increase in VO 2 max ( P = 0.03) and an improvement in the patients’ distribution according to the Shvartz fitness classification after rehabilitation.
Discussion
The four-week exercise rehabilitation program was associated with an improvement in aerobic capacities in patients with chronic pain. However, in all but one of the 121 patients, the VO 2 max value at the end of the program was below average for gender and age. Maintenance of aerobic training after the end of a rehabilitation programme is essential.
Résumé
Contexte
Il existe chez les patients douloureux chroniques un déconditionnement aérobie qui participe au maintien en situation d’incapacité et de handicap. Notre objectif est d’étudier la variation de la VO 2 max après 4 semaines de réadaptation chez des patients douloureux chroniques.
Méthodes
Il s’agit d’une étude prospective sur 121 patients douloureux chroniques (lombalgie chronique, syndrome douloureux chronique du membre supérieur ou syndrome douloureux chronique multifocal). Nous avons mesuré la VO 2 max à l’aide d’un analyseur d’échanges gazeux au cours d’une épreuve d’effort sur cycloergomètre avant et après 4 semaines de réadaptation associant travail aérobie, renforcement musculaire, ergothérapie et assouplissements.
Résultats
Nous avons observé une amélioration statistiquement significative de la VO 2 max ( p = 0,03) dans notre population, et une amélioration de la répartition des patients selon les catégories de Shvartz après un programme de 4 semaines de réadaptation.
Discussion
Le programme de réadaptation proposé permet une amélioration des capacités aérobies chez les patients douloureux chroniques. Cependant, la VO 2 max à la fin du programme reste chez 120 patients, inférieure à la moyenne pour l’âge et le sexe. La poursuite d’une activité aérobie régulière est donc indispensable au décours du programme de réadaptation.
1
English version
1.1
Introduction
Deconditioning syndrome is one reason for poor effort tolerance and a progressive decrease in physical ability in patients with chronic low back pain (LBP) (particularly in patients who have been off work for a long period) . VO 2 max is defined as the maximum volume of gaseous oxygen that the body can take up per unit time during maximal aerobic exercise; it corresponds an individual’s maximum capacity to transport and use oxygen and thus reflects his/her physical fitness. In chronic LBP patients, it has been hypothesized that a progressive decrease in physical activity impacts the maximum aerobic capacity; this creates a vicious circle (the “deconditioning spiral”) in which inactivity leads to the aerobic deconditioning, which in turn leads to a reduction in physical activity .
In previous work , we discussed this hypothesis and evidenced objective deconditioning and a collapse in aerobic capacity by measuring VO 2 max (using indirect calorimetry) during a cycle ergometer exercise tolerance test in patients with chronic LBP and patients suffering from musculoskeletal pain at various body sites (chronic pain of upper limb and multifocal chronic pain). We therefore decided to apply the deconditioning theory to chronic musculoskeletal pain more broadly and offer multidisciplinary exercise rehabilitation programs to chronic pain sufferers.
The primary objective of the present study was to measure VO 2 max before and after four weeks of exercise rehabilitation in patients suffering from chronic pain at various body sites. We hypothesized that effort training would improve aerobic capacities in all patients, regardless of the type of chronic pain syndrome. The study’s secondary objectives were to characterize variations in objective and subjective fitness parameters after the rehabilitation programme and to look for correlations with Δ VO 2 max.
1.2
Materials and methods
1.2.1
The study population
Patients (aged from 18 to 60) hospitalized in the physical medicine and rehabilitation department at Château-Renault hospital (Château-Renault, France) in 2010 for chronic pain syndrome (chronic muscle or joint pain for more than three months) and who had participated in an exercise rehabilitation programme were eligible for inclusion in the study. The patients were variously in work, on sick leave or unemployed. Following application of the inclusion criteria, 121 patients were selected for this cohort study ( Table 1 ). The mean ± SD length of time off work prior to hospitalization was 10.1 ± 8.6 months. Eighty patients had been off work for more than 6 months.
| Total study population | CLBP | ULP | MPS | P | |
|---|---|---|---|---|---|
| n | 121 | 61 | 34 | 26 | |
| Age (years) | 42.1 ± 9.4 | 41.6 ± 8.6 | 39.3 ± 10.6 | 46.1 ± 8.1 | ≤ 0.05* |
| Gender (M/F) | 63/58 | 43/19 | 11/23 | 9/16 | 0.005 |
| BMI (kg/m 2 ) | 26.6 ± 5.3 | 26.3 ± 5.2 | 27.2 ± 5.6 | 26.4 ± 5.2 | NS |
| Time since onset of disability (months) | 10 ± 8.7 | 8.4 ± 6.9 | 10.6 ± 9.7 | 12.2 ± 10.7 | NS |
In general, chronic pain syndrome patients admitted to our department for rehabilitation undergo an exercise tolerance test, during which VO 2 max is measured by indirect calorimetry. Patients over the age of 50 or those with two or more cardiovascular risk factors prior to admission undergo an exercise tolerance test with a cardiologist, in order to detect any contra-indications to participation in an aerobic rehabilitation programme.
Our department’s routine clinical evaluation procedure was applied in all cases. In accordance with French data protection guidelines, all patients were informed that their personal data would be computer-processed. Approval by an independent ethics committee was not required because the protocol did not involve any changes in the patients’ normal standard of care or any additional procedures and analyses.
The study participants were classified into three groups, as a function of the type of pain ( Table 1 ):
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the chronic LBP group: LBP pain with or without irradiation to the leg, and no known neurological disorders;
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the chronic pain of upper limb (ULP) group: chronic pain in one upper limb, with or without specific symptoms of musculoskeletal disorder, and no indication for a surgical treatment;
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the multifocal pain syndrome (MPS) group: pain at several body sites (i.e. LBP plus pain in one or both arms).
1.2.2
Methods
All the patients were evaluated by our department’s physical and rehabilitation medicine specialists, physiotherapists and occupational therapists before and after the rehabilitation programme. The evaluation included a maximal exercise tolerance test on a Cardiocontrol ® cycle ergometer, with measurement of VO 2 max. This was an incremental test starting at a power of 30 W, with a 30 W increment every three minutes. The pedalling rate was maintained at 60 rotations per minute throughout the test. The participants were told that the goal was to achieve the best possible level of performance, despite the pain. The VO 2 measurement was performed using a MedGraphics Cardiorespiratory Diagnostic Systems ® gas exchange analyser; the highest VO 2 value recorded during the test was considered to be the VO 2 max. The measuring equipment was calibrated at the start of each session (which comprised 4 to 6 exercise tolerance tests over a half-day period). The heart rate was monitored continuously throughout the test and the arterial blood pressure was measured before the exercise tolerance test, at each increment and after three minutes of rest at the end of the test. The exercise tolerance test was stopped in the event of exhaustion (i.e. the test was submaximal) or if the theoretical maximum heart rate (HR max , defined by the ‘220 minus age” equation) was reached (i.e. the test was maximal). The VO 2 max values were related to the participant’s body weight and expressed in mL/kg/min. The values were compared with Shvartz and Reibold’s normative values for age and gender and participants were classified into seven fitness levels: 1, excellent; 2, very good; 3, good; 4, average; 5, fair; 6, poor; 7, very poor. The perceived exertion rating (PER, on the Borg scale ) was recorded before the test, immediately afterwards and then after 3 minutes of rest.
Poor exercise tolerance can be measured in a number of objective tests:
- •
the Sorensen test . The subject lies in the prone position, with his/her legs strapped to the table and the upper body hanging over the edge. With his/her arms folded across the chest, the subject has to maintain the unsupported upper body in a horizontal position for as long as possible. This test evaluates the endurance of the spinal extensor muscles;
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the Progressive Isoinertial Lifting Evaluation (PILE), developed by Mayer et al. . The patient must lift a weight off the ground to waist height four times within 20 seconds. The weight is initially 4 kg and is increased by 2.5 kg increments until severe discomfort occurs. The maximum weight lifted (in kg and as a percentage of the subject’s body weight) and the total weights lifted are noted. We evaluated the HR, arterial blood pressure and PER before the test, at the end of the test and after 3 minutes of rest.
The patient’s perception of disability was assessed with self-questionnaires: the Questionnaire d’évaluation de la capacité fonctionnelle (EIFEL, the French language version of the Roland and Morris Disability Questionnaire) for the chronic LBP group , the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire for the ULP group , and both self-questionnaires if the patient suffered from both LBP and chronic pain of upper limb.
All the patients followed a four-week physical exercise programme that comprised a six-hour rehabilitation session five days a week. This session comprises six 10-minute muscle strength exercises (prescribed individually as a function of the one-rep maximum strength evaluated at the start of the programme) spread over the morning, an hour of aerobic work, an hour of stretching and 30 to 45 minutes of occupational therapy (a combination of strength and flexibility exercises).
We then analyzed and compared the data collected before and then after four weeks of physical exercise rehabilitation.
1.2.3
Statistical analysis
Quantitative variables were compared using Student’s test and the mean frequencies of qualitative variables were compared in an analysis of variance. Correlations between quantitative parameters were studied with the correlation module provided by Statview software. The threshold for statistical significance was set to P < 0.05. The normality of the data distribution was checked before statistical tests were applied with a Kolmogorov-Smirnov test.
1.3
Results
1.3.1
Changes in VO 2 max after a four-week physical exercise programme
We observed a statistically significant increase in VO 2 max ( P = 0.03) after four weeks of rehabilitation ( Table 2 ). For the other test parameters, we observed a statistically significant increase in the maximum power ( P = 0.0001), an increase in VO 2 at the ventilatory threshold 1 (VT1) (although this did not achieve statistical significance) and a significant decrease in HR max ( P = 0.007, although this remained at more than 90% of the theoretical maximum).
| Before rehabilitation | After rehabilitation | P | |
|---|---|---|---|
| VO 2 at the ventilatory threshold VT1 (mL/kg/min) | 11.4 ± 8.4 | 12.6 ± 11.1 | NS |
| Ventilatory threshold power VT1 (W) | 57.1 ± 54.9 | 64.7 ± 24 | NS |
| VO 2 max (mL/kg/min) | 22.2 ± 5.7 | 25.2 ± 15.3 | 0.03 |
| Maximum power (W) | 132.2 ± 43.9 | 153.3 ± 51 | 0.0001 |
| HRmax (% theoretical) | 91.9 ± 7.5 | 90.3 ± 7.9 | 0.0007 |
The change in VO 2 max did not depend significantly on gender or age. There were no statistically significant differences in the change in VO 2 max when comparing the three pain subgroups (1.4 ± 3.1 mL/kg/min in the AP group, 1.9 ± 3.4 mL/kg/min in the CLBP group and 2.5 ± 4.2 mL/kg/min in the MPS group).
The patients’ distribution according to the Shvartz fitness classification before and after rehabilitation is shown in Table 3 . The Shvartz classification was not predictive of the final EIFEL or DASH scores or the maximum weight lifted in the PILE. There were no significant inter-group differences in the distribution of the Shvartz classes either before or after the rehabilitation programme.
| Before rehabilitation | |||||
|---|---|---|---|---|---|
| 7 (very poor) | 6 (poor) | 5 (fair) | Total | ||
| After rehabilitation | 7 (very poor) | 29 | 12 | 1 | 42 |
| 6 (poor) | 57 | 4 | 0 | 61 | |
| 5 (fair) | 3 | 8 | 7 | 18 | |
| 4 (average) | 0 | 0 | 0 | 0 | |
| 3 (good) | 0 | 0 | 1 | 1 | |
| Total | 88 | 24 | 9 | 121 | |
1.3.2
Changes in objective measures of disability after four weeks of exercise rehabilitation
We observed a statistically significant increase in the Sorensen test time ( P = 0.0001) and the associated cardiac cost ( P = 0.02) after four weeks of rehabilitation ( Table 4 ).
| Before rehabilitation | After rehabilitation | P | |
|---|---|---|---|
| PILE | |||
| Maximum weight lifted in the PILE (kg) | 27.5 ± 12.5 | 36.4 ± 15.5 | 0.0001 |
| Maximum weight lifted in the PILE (% bodyweight) | 32.8 ± 16.6 | 46.8 ± 18.6 | 0.0001 |
| Total weight lifted in the PILE (kg) | 478.9 ± 368 | 804.9 ± 427 | 0.0001 |
| Relative cardiac cost in the PILE | 16.7 ± 11.2 | 17.4 ± 10.5 | NS |
| Sorensen test (n = 110) | |||
| Sorensen test time (seconds) | 71 ± 34 | 144.4 ± 60.9 | 0.0001 |
| Relative cardiac cost in the Sorensen test | 16.0 ± 9.4 | 18.8 ± 8.6 | 0.02 |
For the PILE, we observed statistically significant increases in the maximum weight lifted (whether measured in kg or as a percentage of body weight [ P = 0.0001]) and the total weight lifted ( P = 0.0001) after four weeks of rehabilitation. We also observed an increase in the associated cardiac cost, although it did not achieve statistical significance.
1.3.3
Changes in subjective measures of disability after four weeks of exercise rehabilitation
We observed a statistically significant decrease in the EIFEL and DASH scores after four weeks of rehabilitation ( P = 0.0001) ( Table 5 ). After four weeks of rehabilitation, there was a significant decrease in the PER noted at the start and end of the PILE ( P = 0.04), at the start and end of the exercise tolerance test ( P = 0.0001) and three minutes after the end of the exercise tolerance test.
| Before rehabilitation | After rehabilitation | P | |
|---|---|---|---|
| EIFEL score (n = 78) | 9.9 ± 4.8 | 4.1 ± 4.5 | 0.0001 |
| DASH score (n = 57) | 81.6 ± 18.6 | 60.1 ± 20.4 | 0.0001 |
| Borg perceived exertion rating | |||
| Before the PILE | 4.5 ± 5.9 | 3.3 ± 2.3 | 0.04 |
| After the PILE | 5.8 ± 7.6 | 4.3 ± 2.4 | 0.04 |
| Before the exercise tolerance test | 3.8 ± 2.3 | 2.2 ± 2.8 | 0.0001 |
| After the exercise tolerance test | 6.2 ± 1.9 | 4.8 ± 2.8 | 0.0001 |
| Three minutes after the end of the exercise tolerance test | 4.9 ± 4.8 | 2.9 ± 1.8 | 0.0003 |
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