Volume 87, Issue 6, Pages 741-748 (June 2006)

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Changes in Physical Capacity During and After Inpatient Rehabilitation in Subjects With a Spinal Cord Injury

Abstract

Haisma JA, Bussmann JB, Stam HJ, Sluis TA, Bergen MP, Dallmeijer AJ, de Groot S, van der Woude LH. Changes in physical capacity during and after inpatient rehabilitation in subjects with a spinal cord injury.

Objective

To assess changes in physical capacity and its determinants in persons with a spinal cord injury.

Design

Prospective cohort study. Measurements at the start of active rehabilitation (t1), 3 months later (t2), at discharge (t3), and 1 year after discharge (t4).

Setting

Eight rehabilitation centers in The Netherlands.

Participants

A total of 186 subjects at t1 and 123 subjects at t4.

Interventions

Not applicable.

Main Outcome Measures

Peak aerobic power output (POpeak), peak oxygen uptake (Vo2peak), muscle strength of the upper extremity (manual muscle test, handheld dynamometry), and respiratory function (forced expiratory flow per second, forced vital capacity).

Results

Random coefficient analysis demonstrated that the POpeak, Vo2peak, strength, and respiratory function improved during inpatient rehabilitation, and that Vo2peak, strength, and respiratory function continued to improve after discharge. Age, sex, and level and completeness of lesion were determinants of the change in components of physical capacity.

Conclusions

Physical capacity improves during inpatient rehabilitation, and some components continue to improve after discharge. Subpopulations have a different level of (change in) physical capacity. The components of physical capacity are related; intervention studies are needed to confirm whether training 1 component could improve another component.

Key Words: Exercise test , Muscles , Rehabilitation , Respiratory function tests , Spinal cord injuries

Article Outline

• Abstract

• Methods

• Participants

• Design

• Procedure

• POpeak and Vpeak

• Strength of the upper extremity

• Respiratory function

• Analyses

• Change in the physical capacity during and after inpatient rehabilitation

• Relation between the change in physical capacity and personal and lesion characteristics

• Relation between the different components of physical capacity

• Results

• Participants

• Change in the Physical Capacity During and After Inpatient Rehabilitation

• Relation Between the Change in Physical Capacity and Personal and Lesion Characteristics

• Age

• Sex

• Level of the lesion

• Completeness of the lesion

• Relation Between the Different Components of Physical Capacity

• Discussion

• Change in Physical Capacity During and After Inpatient Rehabilitation

• Vpeak and POpeak

• Strength of the Upper Extremity

• Respiratory Function

• Relation Between the Change in Physical Capacity and Personal and Lesion Characteristics

• Age

• Sex

• Level of the lesion

• Completeness of the lesion

• Relation Between the Different Components of Physical Capacity

• Study Limitations

• Conclusions

• Acknowledgment

• References

• Copyright

PHYSICAL CAPACITY IS the combined ability of the cardiovascular, the respiratory, and the musculoskeletal systems to attain a certain level of activity.1 The different components of physical capacity (eg, power output, oxygen uptake, muscle strength, respiratory function) are related.2, 3, 4 Additionally, the components are influenced by personal and lesion-related factors and by training.4, 5, 6, 7, 8

Physical capacity is reduced in people with spinal cord injuries (SCIs) because of muscle weakness, loss of autonomic control below the level of injury,9, 10, 11 reduced activity, and subsequent changes in metabolic and vascular function.5, 9, 12, 13 A reduced physical capacity is an important determinant of the health status of SCI subjects because it exposes them to increased risk of complications6, 13 and is related to a reduced level of functioning and quality of life.6, 13, 14, 15 Therefore, an important goal of rehabilitation is to reverse the debilitative cycle of a reduced physical capacity that leads to reduced activity and functioning, which in turn further reduces physical capacity, and so on.13, 14 This reversal may be achieved by improving physical capacity through rehabilitation training programs.

Knowledge about the change in physical capacity during inpatient rehabilitation is a prerequisite to developing optimal rehabilitation programs and for setting realistic individual rehabilitation goals. After discharge, there are less training opportunities and more activities of daily living (ADLs) to perform. Because physical capacity is related to the performance of ADLs, it is especially important to determine whether people with SCI can maintain their levels of physical capacity after discharge.16, 17, 18

Research that has focused on physical capacity in SCI has often been limited by the particular study’s population or design. Most research has focused on one component of physical capacity (eg, either peak oxygen uptake [Vo2peak], or muscle strength, or respiratory function). More than 1 component of physical capacity, however, should be studied simultaneously to analyze the relation between the different components.1 Follow-up studies have found significant differences between admission and discharge scores,1, 19 but because it has been suggested that most changes occur during the first phase of rehabilitation,20 it is important to investigate the change over shorter periods of time. Because there is some debate as to whether the level of activity during daily life is adequate to maintain physical capacity after discharge,17, 21 a longitudinal study is needed to gain more insight into the changes that occur after inpatient rehabilitation. Age, sex, and level and completeness of the lesion have been found to be factors related to the physical capacity in cross-sectional studies,5, 6 and longitudinal data will give insight into the influence of these factors on the change in physical capacity.

Our main purpose in this study was to determine what changes occur in the components of physical capacity (ie, peak aerobic power output [POpeak], Vo2peak, muscle strength of the upper extremity, respiratory function) during inpatient rehabilitation and in the year after discharge in people with SCI who were wheelchair-dependent. Furthermore, we wanted to assess the association between personal and lesion characteristics, and the change in physical capacity over time. Finally, we wanted to study the relation between the different components of physical capacity.

Methods

Participants

This study was part of the Dutch research program “Physical strain, work capacity, and mechanisms of restoration of mobility in the rehabilitation of persons with a spinal cord injury.” Subjects with SCI who were in their initial inpatient rehabilitation were recruited from 8 specialized rehabilitation centers. Subjects were eligible for inclusion if they were between 18 and 65 years of age, were wheelchair-dependent, had sufficient comprehension of the Dutch language to understand the purpose of the study and its testing methods, and did not have a progressive disease or a psychiatric condition that would interfere with constructive participation. Subjects were excluded from the study if they had cardiovascular contraindications for exercise,22 a resting diastolic blood pressure greater than 90mmHg, or a systolic blood pressure greater than 180mmHg. Additionally, subjects were excluded from the maximal exercise test and muscle strength assessments if they had compromising complaints of the musculoskeletal system. Within 2 weeks of admission to rehabilitation, eligible subjects were informed about the study by a physician and invited to participate. Subjects had 1 week to consider participating, after which a physician or a nurse not involved in the research program requested consent. The medical ethics committee approved the experimental protocol, and all subjects gave their written informed consent before participating.

Design

Subjects admitted to rehabilitation from 1999 through 2004 were included in the study if they met eligibility criteria. They were assessed at 4 points in time (called measurement times): at the start of active inpatient rehabilitation when the subject could sit in a wheelchair for at least 3 hours (t1), 3 months later (t2), at discharge (t3), and 1 year after discharge (t4). If a subject was discharged within 1 month after t2, their assessment at t2 was considered a “discharge” assessment and was included in the analysis of physical capacity at t3. If a subject no longer used a wheelchair, the previously collected data were analyzed, but no new data were collected.

Subject characteristics and level and completeness of the lesion and physical capacity scores were determined according to a standardized procedure. Tetraplegia was defined as a lesion at or above the T1 segment and paraplegia as a lesion below the T1 segment. A complete lesion was defined as motor complete, that is, American Spinal Injury Association (ASIA) grade A or B.23 An incomplete lesion was defined as ASIA grade C or D.23 In each of the 8 rehabilitation centers, a trained research assistant collected the data. The same testing equipment (ie, research wheelchair, treadmill,a dynamometer,b Oxycon Deltac) was used for every measurement, after standardized calibration.

Procedure

POpeak and Vo2peak

To determine POpeak and Vo2peak, subjects performed a graded maximal wheelchair exercise test on a motor-driven treadmill.a Before testing, subjects were asked to eat a light meal only, to refrain from smoking and drinking coffee or alcohol 2 hours before testing, and to void their bladders. The testing protocol and equipment has been described previously by Kilkens et al.24 For each subject, and at every measurement time, a drag test was used to calculate the power output for the wheelchair-user system on the treadmill at increasing inclinations.25

Subjects performed 2 blocks of submaximal exercise of 3 minutes each, separated by a 2-minute rest. The treadmill incline was horizontal during the first block and then set at .36° during the second block. Treadmill velocity was set at 2km/h for subjects with tetraplegia and at 4km/h for subjects with paraplegia. In some subjects with a low cervical lesion, we used a protocol with a velocity of 3km/h. After 2 minutes of rest, the maximal exercise test followed at the same constant velocity, and the inclination was increased .36° every minute. The test was terminated when the subject was exhausted or could no longer keep pace with the speed of the treadmill. The Vo2peak (in L/min) was defined as the highest value of oxygen consumption recorded during 30 seconds. The POpeak (in watts) was defined as the power output at the highest inclination that the subject could maintain for at least 30 seconds.

Strength of the upper extremity

To determine the strength of the upper extremity, the shoulder abductors, internal and external rotators, elbow flexors and extensors, and wrist extensors in both arms were tested with the manual muscle test (MMT). This test was performed in standardized positions, in which subjects performed a movement either with or without gravity, or against resistance.26 The strength was rated on a scale ranging from 0 to 5.26 Summing the scores of the 12 muscle groups gave an MMT sum score (maximum, 60).

The muscle groups (with exception of the wrist extensors) that scored 3 or greater on the MMT were tested with handheld dynamometryb (HHD) according to a standardized protocol.27 The break test was used: the subject exerted a maximal force against a dynamometer and the examiner applied sufficient resistance to just overcome the force exerted by the subject.28 The maximum force (in newtons) of the 10 muscle groups was summated. Only when an MMT or HHD score was available for all muscle groups (ie, 12 or 10, respectively) was a sum score calculated and included in the estimation of the muscle strength at that measurement time.

Respiratory function

Flow-volume curves were made with the Oxycon Deltac to assess respiratory function. Three repeated curves were made and if the resultant curve did not have its characteristic shape, an extra measurement was made.29 The forced vital capacity (FVC) (in liters) and forced expiratory flow per second (FEV1) (in liters) for each subject were additionally expressed as a percentage of what that subject was expected to score in comparison with an age, sex, and height-matched able-bodied population.30

Analyses

We used random coefficient analysisd to analyze the changes over time in physical capacity and its determinants.31, 32 An important advantage of this method is that it considers the dependency of repeated assessments within 1 subject and within 1 rehabilitation center. Additionally, the analyses can be done even with missing values.31, 32 This offers the advantage over repeated-measurements analysis of variance that more subjects can be included, which gives a more realistic representation of the group performance at each measurement time. Thus, we included subjects in the analyses when 1 or more components of physical capacity at 1 or more measurement times could be determined, and we could adequately assess the change in physical capacity over time with varying group composition.31, 32

Change in the physical capacity during and after inpatient rehabilitation

We made a basic regression model for the change in each component of physical capacity. Time was included in the model not as a single continuous variable, but as a set of dummy variables, with the physical capacity at discharge designated as the reference variable. In this analysis, the physical capacity at discharge was estimated by the intercept. The differences between the physical capacity at discharge and the physical capacity at the other measurement times were estimated by the coefficients for these measurement times. Estimates of the physical capacity at the other measurement times were obtained by adding these coefficients to the intercept. The model had to include all dummy variables to permit a valid assessment of the physical capacity.

Relation between the change in physical capacity and personal and lesion characteristics

To determine whether the independent variables age, sex, and level and completeness of the lesion were related to the change in physical capacity over time, they and their interaction terms with the dummy variables were alternately added to the basic model. Then, the variables and interaction terms with a P value of .10 or less were simultaneously added to the basic model. The nonsignificant variables (P>.05) were removed through backward elimination. To make a valid analysis of the relation between an independent variable and the change in physical capacity over time, we had to include all its interaction terms even if the relation proved significant over only 1 time interval.

Relation between the different components of physical capacity

To investigate whether the components of physical capacity were related, we first analyzed the association between the Vo2peak, muscle strength and respiratory function, and the change in POpeak; the association between muscle strength and respiratory function and the (change in) Vo2peak was analyzed separately. In both instances, we controlled for those independent variables that contributed significantly to the POpeak and Vo2peak in the respective preceding model by including these variables in the model. We made models for both the POpeak and Vo2peak according to the procedure described in the above paragraph. This resulted in 2 models with independent variables and the components of physical capacity that were significantly related to the POpeak or Vo2peak.

Results

Participants

At the start of rehabilitation, the group included 186 subjects; a year after discharge there were 123 subjects. During the study, 58 subjects dropped out at some point: 16 subjects became wheelchair-independent, 25 refused further participation, 9 subjects could not be traced, and 8 subjects died. There were several reasons for not collecting data at any particular measurement time: 44 subjects were discharged within 3 months after admission, hence they did not perform a t2 measurement; 20 subjects had neurologic deficits too large to permit them to perform the test; 14 subjects had cardiovascular or musculoskeletal contraindications; 9 subjects had a halo traction or other fixation; 6 subjects had other pathology (eg, infection, pressure ulcer) that prevented assessment; and technical problems prevented assessment of 8 subjects. Table 1 lists the group sizes, means and standard deviations (SDs) for subject characteristics, lesion characteristics, and physical capacity scores at the different measurement times for subjects from whom at least 1 component of physical capacity could be obtained at that particular measurement time.

Table 1.

Subject and Lesion Characteristics and Physical Capacity Scores at the 4 Measurement Times


Characteristics and Scores	Start		Three Months		Discharge		Year After Discharge
Characteristics and Scores	n	Mean ± SD	n	Mean ± SD	n	Mean ± SD	n	Mean ± SD
Age (y)
TP	75	39±13	66	39±13	66	40±13	42	39±13
PP	110	41±15	72	41±15	102	41±15	81	42±14
Sex (% men)
TP	76	74	66	73	66	76	42	74
PP	110	75	72	78	103	74	81	74
Height (m)
TP	75	1.78±0.09	66	1.77±0.10	65	1.77±0.09	42	1.76±0.09
PP	108	1.78±0.10	70	1.79±0.08	100	1.79±0.10	80	1.78±0.09
Body mass (kg)
TP	75	70±14	65	72±14	66	74±15	42	77±17
PP	110	73±14	71	74±14	101	75±14	81	77±17
Time since injury (d)
TP	75	108±67	65	212±76	65	388±176	42	787±206
PP	110	102±62	71	190±75	101	269±117	81	657±138
Complete (% complete)
TP	76	66	63	60	66	52	41	54
PP	109	69	71	73	102	72	80	73
Peak heart rate (bpm)
TP	22	112±19	22	111±18	35	117±22	16	122±28
PP	80	147±21	62	153±26	87	152±25	61	154±27
Vo2peak (L/min)
TP	22	0.85±0.25	22	0.85±0.36	35	0.99±0.37	17	1.17±0.43
PP	80	1.07±0.37	63	1.22±0.37	87	1.32±0.43	62	1.31±0.47
POpeak (W)
TP	23	17±9	23	16±7	35	25±16	16	30±21
PP	76	35±18	63	44±18	90	48±22	61	51±23
MMT sum score (/60)
TP	70	39±15	62	41±15	65	45±15	38	47±13
PP	105	58±7	71	59±3	99	59±3	79	59±2
HHD sum score (N)
TP	29	1076±495	30	1273±442	35	1473±523	23	1485±647
PP	81	1668±482	57	1810±488	71	1934±523	57	1992±508
FEV1 (L)
TP	71	2.42±1.00	64	2.52±0.94	64	2.94±0.98	41	3.09±1.09
PP	104	2.95±1.00	71	3.11±0.83	100	3.37±0.99	73	3.41±0.98
FEV1 (% predicted)
TP	71	64±25	64	66±20	64	77±22	41	81±24
PP	104	77±22	71	80±18	100	86±20	73	88±21
FVC (L)
TP	71	2.89±1.30	64	2.96±1.05	64	3.55±1.23	41	3.75±1.34
PP	104	3.59±1.25	71	3.81±1.03	100	4.15±1.21	73	4.21±1.18
FVC (% predicted)
TP	71	63±26	64	65±19	64	77±22	41	82±24
PP	104	78±25	71	81±19	100	88±21	73	90±20

NOTE. Subjects were included when at least 1 component of physical capacity was determined at that particular measurement time.

Abbreviations: PP, subjects with paraplegia; TP, subjects with tetraplegia.

Change in the Physical Capacity During and After Inpatient Rehabilitation

The POpeak, Vo2peak, muscle strength, and respiratory function improved during inpatient rehabilitation, and the Vo2peak, muscle strength, and respiratory function continued to improve after discharge. Fig 1, Fig 2, Fig 3 show the change in physical capacity over time as estimated with the basic regression model.

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Fig 1. Change in Vo2peak and POpeak as calculated from the basic model.

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Fig 2. Change in MMT sum score (maximum, 60) and HHD score as calculated from the basic model.

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Fig 3. Change in FVC and FEV1 as a percentage of the predicted value (compared with an age-, sex-, and height-matched able-bodied population) as calculated from the basic model.

Relation Between the Change in Physical Capacity and Personal and Lesion Characteristics

Table 2 presents data on the association between the change in physical capacity and the independent variables. The respective regression coefficients represent the change in outcome score associated with an increase in the independent variable of 1 unit. Because table 2 presents data after backward elimination, the dummy variables and significantly contributing variables and interaction terms are given.

Table 2.

Data on the Longitudinal Relation Between Subject and Lesion Characteristics and the Change in Physical Capacity


Independent Variable	POpeak (W)	Vo2peak (L/min)	MMT Sum Score	HHD (N)	FVC (%)	FEV1 (%)
Discharge	49(38to59)	1.13(1.03to1.24)	51(47to54)	1935(1684to2186)	76(66to86)	81(76to86)
Δt1−t3⁎	−22(−28to−15)	−0.18(−0.29to−0.07)	−6(−9to−4)	−642(−850to−434)	−14(−22to−7)	−10(−15to−5)
Δt2−t3†	−10(−15to−5)	−0.08(−0.19to0.02)	−3(−5to−1)	−379(−559to−199)	−7(−14to0)	−7(−11to−2)
Δt3−t4‡	6(−2to14)	0.22(0.08to0.37)	0.1(−1.1to1.4)	135(−53to323)	12(5to18)	2(−1to6)
Sex§	−14(−20to−7)	−0.35(−0.48to−0.23)	NS⁎⁎	−575(−742to−408)	NS	NS
Age	−0.3(−0.5to−0.1)	NS	0.01(−0.06to0.09)	−7(−13to−1)	0.16(−0.05to0.37)	NS
Level∥	11(7to15)	0.23(0.11to0.35)	4(2to5)	348(215to481)	6(1to10)	2(−3to8)
Complete¶	NS	NS	NS	99(25to173)	−5(−8to−2)	−1(−5to3)
Sex by t1−t3#	6(1to12)	NS	NS	154(34to274)	NS	NS
Sex by t2−t3#	4(0to9)	NS	NS	132(20to244)	NS	NS
Sex by t3−t4#	−1(−7to5)	NS	NS	−51(−167to65)	NS	NS
Age by t1−t3	0.19(0.02to0.35)	NS	−0.01(−0.06to0.04)	4.3(0.2to8.4)	0.09(−0.09to0.27)	NS
Age by t2−t3	0.10(−0.03to0.24)	NS	0.01(−0.02to0.05)	3(−1to7)	0.09(−0.08to0.26)	NS
Age by t3−t4	−0.08(−0.28to0.13)	NS	0.04(0.01to0.06)	−1(−5to3)	−0.23(−0.39to−0.08)	NS
Level by t1−t3	NS	−007(−0.19to0.05)	6(4to7)	138(11to265)	NS	5.2(0.3to10.2)
Level by t2−t3	NS	0.01(−0.11to0.13)	2(1to4)	107(−7to221)	NS	3.9(−0.5to8.3)
Level by t3−t4	NS	−0.20(−0.36to−0.04)	−1.3(−2.1to−0.5)	−6(−129to117)	NS	−2(−5to2)
Complete by t1−t3	NS	NS	NS	NS	NS	−6(−11to−1)
Complete by t2−t3	NS	NS	NS	NS	NS	1(−4to6)
Complete by t3−t4	NS	NS	NS	NS	NS	1(−3to5)

NOTE. All results are regression coefficients(β) and 95% confidence intervals(CIs) for the model after backward elimination. The regression coefficients represent the change in outcome associated with an increase in the independent variable of 1 unit.

⁎

The difference in physical capacity between the start of rehabilitation and discharge.

†

The difference between t2 and discharge.

‡

The difference between discharge and 1 year after discharge.

0=men; 1=women.

∥

0=tetraplegia; 1=paraplegia.

0=incomplete; 1=complete.

Sex by t1−t3 represents the relation between sex and the change in outcome during inpatient rehabilitation; sex by t2−t3 represents this relation between t2 and discharge; and sex by t3−t4 represents this relation between discharge and 1 year after discharge.

⁎⁎

Independent variable proven not significant (NS) in previous analyses and therefore not entered into this model.

Age

Age was significantly related to the POpeak and HHD score: an increase in age of 1 year was associated with a decrease of 0.3W or 7N, respectively. During inpatient rehabilitation the improvement in POpeak and HHD was significantly less in older subjects. After discharge, the MMT score improved significantly more in older subjects, whereas the percentage of FVC was significantly less improved in older subjects.

Sex

Men had a significantly greater POpeak, Vo2peak, and HHD score than women (14W, .35L/min, 575N greater, respectively). During inpatient rehabilitation the improvement in POpeak and HHD score was significantly greater in men than in women.

Level of the lesion

In subjects with tetraplegia, the POpeak, Vo2peak, muscle strength, and percentage of FVC were significantly lower than in those with paraplegia. During inpatient rehabilitation, the improvement in muscle strength and percentage of FEV1 was greater in tetraplegic subjects. After discharge, the Vo2peak and MMT improved more in this group.

Completeness of the lesion

Subjects with a complete lesion had a significantly greater HHD score and a significantly lower percentage of FVC than subjects with an incomplete lesion. In subjects with a complete lesion, the improvement in percentage of FEV1 during inpatient rehabilitation was significantly greater than in subjects with an incomplete lesion.

Relation Between the Different Components of Physical Capacity

Table 3 presents data on the association between the Vo2peak, muscle strength, respiratory function, and the POpeak in 1 column, and on the association between muscle strength and respiratory function, and the Vo2peak in the other column. The respective regression coefficients represent the change in POpeak or Vo2peak associated with an increase in Vo2peak, strength, or respiratory function of 1 unit. The level of lesion, the Vo2peak, the HHD score, and the percentage of FVC were significantly associated with the POpeak. For example, an increase in strength of 100N was associated with an increase in POpeak of .87W (regression coefficient, .0087, multiplied by 100N) (see table 3). Sex, the HHD score, and percentage of FEV1 were significantly associated with the Vo2peak.

Table 3.

Data on the Longitudinal Relation Between the Components of Physical Capacity


Independent Variable	POpeak (W)	Vo2peak (L/min)
Discharge	−23.5(−30to−17.1)	0.12(−0.09to0.32)
Δt1−t3⁎	−3.8(−5.9to−1.7)	−0.07(−0.13to−0.01)
Δt2−t3†	−0.5(−2.5to1.4)	−0.01(−0.07to0.05)
Δt3−t4‡	0.7(−2.3to3.6)	0.04(−0.04to0.12)
Sex§	NS¶	−0.13(−0.24to−0.02)
Level∥	7.8(4.9to10.6)	NS
Vo2peak (L/min)	29.3(25.8to32.7)	NS
HHD (N)	0.0087(0.0057to0.0117)	0.0004(0.0003to0.0005)
FVC (%)	0.09(0.04to0.14)	NS
FEV1 (%)	NS	0.0039(0.0021to0.0058)

NOTE. All results are regression coefficients (β) and 95% CIs for the model after backward elimination. The regression coefficients represent the change in outcome associated with an increase in the independent variable of 1 unit.

⁎

The difference in physical capacity between the start of active rehabilitation and discharge.

†

The difference between t2 and discharge.

‡

The difference between discharge and 1 year after discharge.

0=men; 1=women.

∥

0=tetraplegia; 1=paraplegia.

Independent variable proven not significant in previous analyses and therefore not entered into this model.

Discussion

Change in Physical Capacity During and After Inpatient Rehabilitation

In accord with Hjeltnes,20 the increase in physical capacity appeared to be greater during the early phase of inpatient rehabilitation than during a later stage (see Fig 1, Fig 2, Fig 3). The fast recovery at the beginning of rehabilitation could be attributed to the start of the learning and training process, as well as to natural recovery and recuperation from trauma and complications.

In contrast to previous suggestions,8, 21 the improvement in Vo2peak, muscle strength, and respiratory function after discharge suggests that the physical activity level during ADLs and during possible outpatient rehabilitation or (sporting) activities was sufficient to improve these components of physical capacity in the present study population. Future analysis of the association between outpatient rehabilitation or physical activity, and the level of physical capacity is required.

Vo2peak and POpeak

During inpatient rehabilitation the POpeak and Vo2peak improved 41% and 24% (increase in score as a percentage of score at t1, as calculated with basic model), respectively, which is within the range reported by others.19, 33 The relatively greater improvement in POpeak over the increase in Vo2peak could be attributed to an improved wheelchair propulsion efficiency.24, 34, 35 In contrast to other studies,17, 36 the POpeak did not change significantly after inpatient rehabilitation. A reason for this could be that wheelchair configuration has an influence on the POpeak.36 One year after discharge, subjects are expected to be trained in the use of their own wheelchairs, and the compulsory use of a research wheelchair (instead of a private, well-adapted wheelchair) at all measurement times may have caused an underestimation of the change in POpeak in our study.

Strength of the Upper Extremity

In our study population, the MMT improved 7% and the HHD score improved 20% (increase in score as a percentage of the score at t1) during inpatient rehabilitation. Hjeltnes and Wallberg-Henriksson33 reported a larger relative change in the MMT score, however, they reported only on subjects with tetraplegia. Our subjects with tetraplegia improved more than did those with paraplegia, therefore the results for our subjects with tetraplegia are comparable to previous findings.33 The MMT score in our subjects changed less than the HHD score, probably because the MMT is limited in its ability to show a continued increase once a muscle group has reached a grade 4 or 5.37, 38, 39

Respiratory Function

The improvement we found during inpatient rehabilitation was similar to that found by Liaw et al40; it may be attributed to natural recovery, but also to a rehabilitation program that included endurance training that may positively influence respiratory function.2, 4, 41 To date, there are no known longitudinal data that support the significant improvement in respiratory function after discharge. Other studies reported a decrease in respiratory function with an increase in time postinjury42 or found no change in respiratory functioning 1 year after injury.43 Differences in design, however, hamper a valid comparison with these studies.

Relation Between the Change in Physical Capacity and Personal and Lesion Characteristics

Age

The decrease in POpeak and HHD with an increase in age, was also found in other cross-sectional studies.5, 44 To date, however, no prospective study has reported that older subjects showed less improvement in these components than did younger subjects.

Sex

The relation found between the subjects’ sex and the change in HHD score could be attributed to the relatively small functional muscle mass in women, and may have contributed to the reduced degree of improvement in POpeak in women during inpatient rehabilitation.45

Level of the lesion

The influence of the level of the lesion on the components of physical capacity is in agreement with previous studies that have more specifically shown a reduction in physical capacity with an increase in affected segments.5, 42, 46, 47 The relatively large improvement in Vo2peak, muscle strength, and percentage of FEV1 in our subjects with tetraplegia was possibly the result of both training and the recovery of partially denervated segments, whereas the improvement in paraplegic subjects was more the result of training. Dallmeijer et al17 did not find this difference in recovery, which may be explained by the fact that their tetraplegic subjects had relatively more musculoskeletal complaints than did their subjects with paraplegia.

Completeness of the lesion

The lower HHD score we found in our subjects with an incomplete lesion (compared with those with a complete lesion) does not seem logical and does not coincide with findings by Dallmeijer et al,48 but could be attributed to our study population. Because we focused on wheelchair-dependent subjects, the relatively well-performing subjects with an incomplete lesion were excluded. Additionally, the inclusion of only those subjects able to perform the tests excluded poorly performing subjects with a complete lesion. This decision may have given a distorted picture of the difference in performance between the 2 groups.

Relation Between the Different Components of Physical Capacity

To date, no other study has assessed the relation between the components of physical capacity on a longitudinal basis. In agreement with our findings, correlation studies show that both the Vo2peak and muscle strength are related to the POpeak, and that muscle strength is related to the Vo2peak.3, 5, 34, 45 Although the relation was significant in this study, a relatively large increase (compared with the initial score) in respiratory function was associated with a relevant change in POpeak or Vo2peak. Janssen et al45 suggested that the different components of physical capacity are limited by the actual active muscle mass and that strength training programs may improve POpeak and Vo2peak. Our findings appear to support this suggestion, but must be interpreted with caution because complete causality cannot be established with our study’s design.

Study Limitations

The methodology of our study had some limitations. First, the reported level of physical capacity may have been overestimated because the tested subjects represented a positive selection of all persons with SCI: they had survived the critical period after injury and were not limited by cardiovascular or musculoskeletal complaints. Second, there was an increase in the proportion of subjects able to perform the maximal aerobic exercise test and muscle strength assessments over time, which probably reflected an improvement in functional status of these additional subjects. This was not necessarily revealed by an improvement in the results and, therefore, the improvement in these components may have been underestimated. Third, because the subjects who were able to perform the tests varied for each component of physical capacity, the results of each component could reflect the performance of different subgroups.

The results on muscle strength of the upper extremity must be interpreted with caution. By summing the scores, information about the change in strength of specific muscle groups could be lost. We used the MMT score because it is widely used in clinical settings; however, it is an ordinal, subjective scale with each increase in grade representing a different increase in strength.38 To facilitate the collection of reliable data, we used a standardized protocol to describe the procedure, and experienced research assistants received training both before and during the study period. The HHD score is presented by a valid and reliable continuous scale, but it has some restrictions: in the assessment of the wrist extensors its reliability is limited, and it does not cover the lower ranges of strength.37, 49, 50, 51 The development of new manageable equipment to measure muscle strength through all ranges and for all muscle groups seems important.

Conclusions

We found positive changes in the different components of physical capacity both during and after inpatient rehabilitation. The continued improvement after discharge was contrary to expectations and illustrates that it is worthwhile to regularly assess the physical capacity of people with SCI after discharge. It is also important to create optimal conditions (eg, educational programs and training facilities) to facilitate further improvement. The results demonstrate that subpopulations show different changes in physical capacity. Specific training and follow-up programs should explore these differences in order to help each patient develop his/her maximal potential physical capacity. The relationships found between the different components of physical capacity suggest that training 1 component could contribute to the improvement of other components, but this must be confirmed by intervention studies.

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Acknowledgments

We thank our research assistants for their extensive work and also the following rehabilitation centers for their collaboration: Rehabilitation Center de Hoogstraat (Utrecht), Rehabilitation Center Amsterdam, Rehabilitation Center Het Roessingh (Enschede), Rehabilitation Center Hoensbroeck, Sint Maartenskliniek (Nijmegen), Rehabilitation Center Beatrixoord (Haren), Rehabilitation Center Heliomare (Wijk aan Zee), and Rijndam Rehabilitation Center (Rotterdam).

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a Department of Rehabilitation Medicine, Erasmus MC, University Medical Center, Rotterdam

b Rijndam Rehabilitation Center, Rotterdam

c Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam

d Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam

e Rehabilitation Center Amsterdam, Amsterdam, The Netherlands.

Reprint requests to Janneke A. Haisma, MD, Dept of Rehabilitation Medicine, Erasmus MC, University Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands

Supported by the Health Research and Development Council of The Netherlands (grant nos. 1435.0003, 1435.0025).

No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated.

a Angio Lode Ergometer; Lode BV, Zernikepark 16, 9747 AN Groningen, The Netherlands.

b MicroFET; Biometrics Europe BV, Kabelstraat 11, 1322 AD Almere, The Netherlands.

c Jaeger Toennies, Nikkelstraat 2, 4823 AB Breda, The Netherlands.

d MlwiN version 1.1; Centre for Multilevel Modelling, Institute for Education, 20 Bedford Way, London, WC1H 0AL, UK.

PII: S0003-9993(06)00201-2

doi:10.1016/j.apmr.2006.02.032

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