Journal of Rehabilitation Medicine 51-4inkOmslag | Page 21

Grip strength after stroke
we decided to use the 0–500 ms time interval in the
current study.
Rate of force development was markedly decreased
in the affected hand at W2, but approached the values
of non-affected hand during the first 6 months post-
stroke. We are not aware of any comparable study on
rate of force development of grip strength. Canning et
al. (9) found that stroke patients have a decreased rate
of force development in elbow flexion and extension
6 weeks after stroke compared with healthy controls.
This difference was no longer present at 25 weeks. In
contrast, McCrea et al. (27) found that rate of force
development in elbow and shoulder muscles is re-
duced several years post-stroke. Similar results have
been reported for the lower limb (10). Interestingly, it
has been demonstrated that stroke patients are able to
move faster if they are asked to do so during a reach-
grip-lift task with a 3-finger grip without decreasing
movement quality (28). Thus, the instruction to move
faster may be effective in increasing training intensity
and facilitating faster functional recovery (28). Our re-
sults indicate that this may be of particular importance
during the first 6 months after stroke.
Sustainability of grip force
These measurements of sustainability of grip force are
comparable to the results reported by Kamimura &
Ikuta (11). They showed that maximum force and the
time until the momentary sustained grip force values
dropped below 80% of maximum force were lower in
the affected vs the non-affected hand. Maximum force
and sustainability of grip force in the non-affected hand
were not different from that of healthy controls. In
particular, participants< 1 month post-stroke decreased
to 80% of maximum force during less than 3 s. This is
also shown by the initial marked drop in the sustained
curve during the first 2–3 s in our study at W2 and W4.
In contrast to the cross-sectional data of Kamimura
& Ikuta (11), the longitudinal data in our study allow
a description of the recovery of sustainability of grip
force. In the current study, the drop in the sustained
force curve in the affected hand was less marked after
6 months, indicating that loss of sustainability of grip
force is most prominent during the first weeks after
stroke.
Kamimura & Ikuta (11) also found a significant
relationship between the sustainability of grip force
and the ability to squeeze objects during ADL (wring
a wet wash-cloth, open a jar, lift a container, wash the
non-paretic arm). They concluded that both maximum
force and the ability to sustain high grip force is es-
sential in squeezing an object. The ability to sustain
high grip force is important for many activities, such
as carrying a suitcase or using tools. However, it is not
255
clear if the sustained grip capacity can be modified by
training and whether it could be successfully included
in strength interventions.
Study limitations
A limitation of this study is the low sample size, which
makes it difficult to draw firm conclusions and to ana-
lyse the effect of sex and age. Moreover, the findings
are limited to patients with mild to moderate stroke.
The patients already had reasonable grip strength
when they entered the study; the profile of recovery
might look different when stroke survivors with no
grip strength had been included. Another potential
limitation is missing values. One participant missed 3
assessments on the non-affected side. However, mea-
surements on the non-affected side remained stable
during the 1-year follow-up, and it seems unlikely that
this has caused biased results. Furthermore, there are
some missing values for the assessment of the sustai-
ned curve after 7 s, which might bias the results for
the last part of the sustained curve. The last part of the
sustained curve could also be biased, according to the
findings by Kamimura & Ikuta (24), who showed that
the first 6 s of the sustained curve are more reliable
than the 10-s period. However, the force curves on
the non-affected side seem to be similar during the
1-year follow-up, both for hand grip and key pinch
force, indicating stable values, except for week 30,
which showed a similar pattern, but slightly lower
values. The latter may in part be explained by lower
values by the patient who had a second minor stroke
at 6 months. Despite these limitations, the longitudinal
data combined with the detailed assessment of various
aspects of grip strength provide new knowledge with
possible relevance for clinical practice.
Possible clinical implications
Our findings may have some clinical implications.
Several meta-analyses and guidelines for stroke reha-
bilitation stress the importance of task-specific train-
ing (29, 30). Even if strength training is common in
stroke rehabilitation, there seems to be little focus on
practising grip strength that is functional in different
hand positions or grip strength capacity related to rate
of force development or sustained muscle activation.
For example, high grip force in the narrow hand posi-
tion is necessary for holding a knife while cutting hard
vegetables, while, in contrast, opening a jar demands
high grip force in the wide hand position. Further-
more, increasing grip force rapidly (e.g. hammering),
and being able to maintain grip force over time are
important during ADL (e.g. carrying a shopping bag,
squeezing objects) and requires task-specific training.
J Rehabil Med 51, 2019