Highlights
- •Regression-based norms were provided for lower limb strength in PwMS.
- •94.9–100% mildly disabled PwMS had ankle dorsiflexion weakness.
- •98.3% PwMS had weakness in at least one lower limb muscle group.
- •Lower limb weakness was most prevalent in ankle dorsiflexion and hip extension.
Abstract
Background
Limb weakness is a major impairment that affects mobility in persons with multiple
sclerosis (PwMS). Specifically, lower limb (LL) weakness can greatly affect gait and
balance, while increasing fall risk and decreasing quality of life. Numerous studies
have compared LL strength of PwMS to healthy controls, however none have objectively
measured strength in all major LL joints (hip, knee, and ankle) in a large number
of PwMS. Additionally, while discrete normative values exist for knee extensors in
PwMS, there has yet to be regression-based normative isometric strength values for
all major LL muscle groups. Therefore, this study aimed to develop gender-specific
regression-based normative prediction equations, with 95% confidence intervals, for
maximal isometric peak torque of major LL muscles in PwMS. A secondary aim was to
characterize the prevalence of LL weakness in PwMS, defined as ≥ 2 SD below values
reported for healthy individuals.
Methods
A convenience sample of 175 (women: n = 135) PwMS participated in a prospective, cross-sectional study where isometric
peak torque of hip flexors, extensors, and abductors, knee flexors and extensors,
and ankle plantarflexors and dorsiflexors were measured using the Biodex System 4
Pro-Dynamometer®. Demographics (age, height, and weight) and disease characteristics
(disease duration and disability) were collected. Performances were separated for
each muscle group into strongest limb and weakest limb. For each gender, regression-based
equations were generated for the LL muscle groups by limb with age, height, weight,
disability, and disease duration as the covariates. Descriptive statistics were used
to examine the frequency of LL weakness by gender and disability level. For comparison
purposes, age-stratified (<30, 30–39, 40–49, 50–59, 60–69, >70 years) and disability-stratified
(mild, moderate, and severe ambulant) discrete peak torque values were also generated
for each gender.
Results
Regression-based normative data are presented for men and women, accounting for age,
height, weight, disability, and disease duration. Men were significantly stronger
(P < 0.001) than women for all LL, with the men's models accounting for a greater percent
of muscle strength variation than women's models for all muscle groups, except for
hip extension. Disability was inversely related to strength in all of the models.
LL weakness was prevalent in hip flexion (m: 47.5%; w: 63.0%) and extension (m: 92.5%;
w: 88.1%), knee extension (m: 30.0%; w: 33.3%) and flexion (m: 25.0%; w: 34.8%), and
ankle plantarflexion (m: 15.0%; w: 10.4%) and dorsiflexion (m: 100.0%; w: 96.3%).
PwMS with mild disability had a high prevalence of ankle dorsiflexion (94.9–100.0%)
and hip extension (81.4–90.0%) weakness.
Conclusions
This study is the first to provide regression-based normative data of bilateral strength
in all major LL muscle groups and clinically useful prevalence data on the occurrence
of weakness in these muscles. Of note, PwMS had a high prevalence of ankle dorsiflexion
and hip extension weakness even when they were only mildly disabled. These findings
can help guide the direction of future interventions and treatments to improve muscle
function in PwMS.
Keywords
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Article info
Publication history
Published online: May 23, 2023
Accepted:
May 22,
2023
Received in revised form:
April 20,
2023
Received:
February 7,
2023
Identification
Copyright
© 2023 Elsevier B.V. All rights reserved.
