Minimal Clinically Important Difference for Quadriceps Muscle Strength in People with COPD following Pulmonary Rehabilitation

Figures & data

Table 1. Anchor and distribution-based methods to estimate the minimal important and detectable differences.

Method	Approach	Statistics
Mean change value	Mean difference (△6MWD > 25m △SGRQ > 4points)	T1 $-$ T0
Anchor-based method	ROC curve	–
	Linear regression analysis	–
Distribution-based method	ES	$({\mathit{mean}}_{T1}-{\mathit{mean}}_{T0})/\sqrt{{(SD}_{T1}^2+{SD}_{T0}^2)/2}$
	0.5 times SD	$0.5\times {\mathrm{SD}}_{\mathrm{T}0}$
	SEM	${\mathrm{SD}}_{\mathrm{T}0}\mathrm{ }\sqrt{(1-r\mathrm{ })}$
	MDC95	${\mathrm{MDC}}_{95}=\mathrm{SE}M\times 1.96\times \sqrt{2}$

Legend: 6MWD, 6-minute walk distance; ES, effect size; MDC₉₅, minimal detectable change at the 95% level of confidence; r, test-retest reliability coefficient; ROC, receiver operator characteristics; SD, standard deviation; SEM, standard error of measurement, SGRQ, St. George’s Respiratory Questionnaire.

Figure 1. Flow diagram of people with chronic obstructive pulmonary disease included in the study. Legend: 1RM, 1 repetition maximum; COPD, chronic obstructive pulmonary disease; HHD, hand-held dynamometry; PR, pulmonary rehabilitation.

Table 2. Sample characterisation.

Characteristics	Participants included (n = 89)	Drop-outs (n = 25)	p-value
Age, years	69.9 ± 7.9	68.7 ± 10.9	0.542
Sex, male n (%)	75 (84)	19 (76)	0.247
BMI, kg/m^2	26.7 ± 5	25.9 ± 5.3	0.275
mMRC	2 [1-3]	2 [1-3]	0.286
Physical activity	0 [0-2]	0 [0-1]	0.433
Smoking status, n (%) Current Former Never	11 (12) 62 (70) 16 (18)	2 (8) 17 (68) 6 (24)	0.705
Packs/year	40 [24-69]	40 [15.6-58]	0.787
Exacerbations/year^1	1 [0-1]	1 [0-3]	0.139
Lung function (post-bronchodilator)
FEV1, L	1.3 ± 0.6	1.3 ± 0.4	0.683
FEV1, %predicted	49.9 ± 18.9	54.6 ± 20.1	0.264
GOLD stages, n (%) I II III IV	11 (12) 26 (29) 42 (47) 9 (10)	3 (12) 8 (32) 10 (40) 2 (8)	0.964
GOLD groups, n (%) A B C D	28 (32) 41 (46) 2 (2) 18 (20)	9 (36) 6 (24) 1 (4) 9 (36)	0.194
CCI, n (%) 1-2 3-4 ≥5	9 (10) 54 (61) 26 (29)	3 (12) 12 (48) 10 (40)	0.515
Medication, n (%) Bronchodilators SABA SAMA LABA LAMA LAMA/LABA combination ICS ICS/LABA combination Xanthines Expectorants Antibiotics	8 (9) 2 (2) 8 (9) 25 (28) 22 (25) 24 (27) 29 (33) 16 (18) 6 (7) 3 (3)	0 (0) 0 (0) 2 (8) 6 (24) 5 (20) 4 (16) 5 (20) 3 (212) 1 (4) 0 (0)	0.172 0.505 0.845 0.805 0.905 0.576 0.668 0.805 0.804 0.402
1RM (leg extension, Kg)	37 ± 13.6	39.6 ± 15	0.442
HHD (leg extension, KgF)	31.3 ± 8.1	27.6 ± 7.4	0.055
6MWD, metres	411.1 ± 132	360.8 ± 119.2	0.076
6MWD, % predicted	85 ± 25.8	76.8 ± 22.3	0.153
SGRQ (total score)	45.6 ± 19.2	41 ± 20.2	0.297

Notes: Values are presented as mean ± standard deviation or median [interquartile range], unless otherwise stated. ¹past-year.

Legend: 1RM, 1 repetition maximum; 6MWD, 6-minute walk distance; AECOPD, acute exacerbation of chronic obstructive pulmonary disease; BMI, body mass index; CCI, Charlson comorbidity index; FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; GOLD - Global Initiative for Chronic Obstructive Lung Disease; HHD, hand-held dynamometry; ICS, inhaled corticosteroids; LABA, long-acting beta-agonists; LAMA, long-acting muscarinic antagonist; LRTA, leukotriene receptor antagonist; mMRC, modified medical research council questionnaire; SABA, short-acting beta-agonists; SAMA, short-acting muscarinic antagonist; SGRQ, St. George’s Respiratory Questionnaire.

Table 3. Outcome measures before and after the 12-week community-based pulmonary rehabilitation programme in people with COPD.

Outcome measure	Baseline	Post-PR	△	% △	p-value	ES
1RM (leg extension, Kg) (n = 65)	37.2 ± 13.2	44.7 ± 17.9	7.5 ± 12.4	24.5 ± 42	<0.001*	0.5
HHD (leg extension, KgF) (n = 70)	31.7 ± 7.7	34.1 ± 8.2	2.1 ± 6.9	9.5 ± 26.5	0.015*	0.2
6MWD, metres (n = 89)	417.8 ± 127.5	460.2 ± 131.2	43.3 ± 63	15.5 ± 28.1	<0.001*	0.7
SGRQ (total score) (n = 89)	45.61 ± 19.2	38.5 ± 18.3	−7.9 ± 10.8	−16.2 ± 28.8	<0.001*	0.4

Notes: Values are presented as mean ± standard deviation. *p < 0.05.

Legend: △, mean change; 1RM, 1 repetition maximum; 6MWD, 6-minute walk distance; ES, Effect size; HHD, handheld dynamometry, PR, pulmonary rehabilitation; SGRQ, St. George’s respiratory questionnaire.

Figure 2. - Linear regression of A) changes in one-repetition maximum (1RM) of quadriceps muscle strength and changes in the six-minute walk test (6MWT) and B) percentage of changes in 1RM of quadriceps muscle strength and changes in the 6MWT.

Figure 3. - Plot of the pooled MCID for one-repetition maximum (1RM) of quadriceps muscle strength. The plot represents the MCID estimates derived in this study, and where appropriate the estimates include the 95% confidence interval (n = 65). Abbreviations: 6MWD, distance performed on six-minute walk test; SD, standard deviation; SEM, standard error measurement; MDC, minimal detectable change.

Table 4. Anchor and distribution-based methods used to compute the minimal clinically important difference of quadriceps muscle strength.

		1RM (leg extension, Kg)	1RM (% change)	HHD (leg extension, KgF)
Anchor methods
Mean difference (6MWD)		6.4 (95%CI 0.1- 12.6)	33.7 (95%CI 18.4- 49)	–
Linear regression (6MWD)		5.9 (95%CI 1.2- 10.6)	19.2 (95%CI 3.1- 35.1)	–
Distribution methods
0.5SD		6.6	–	4.1
SEM		2.6	–	2.9
1.96SEM		5.2	–	5.7
MDC		7.3	–	8.1
ES		0.5	–	0.2
Pooled MCID		5.7	26.9	5.2
MCID ES		0.5	–	0.9

Legend: 1RM, 1 repetition maximum; 6MWD, 6-minute walk distance; ES, Effect size; HHD, handheld dynamometer; MCID, minimal clinically important difference; PR, pulmonary rehabilitation; SD, standard deviation; SEM, standard error of the measurement.

Figure 4. - Plot of the pooled MCID for quadriceps muscle strength assessed with hand-held dynamometer. The plot represents the MCID estimates derived in this study, and where appropriate the estimates include the 95% confidence interval (n = 70). Abbreviations: SD, standard deviation; SEM, standard error measurement; MDC, minimal detectable change.