Spasticity is a common disorder affecting neurological patients with different pathologies such as multiple sclerosis, spinal cord injury or stroke, among others.1 Spasticity has been defined as “impaired sensorimotor control caused by an upper motor neuron lesion presenting with involuntary or sustained muscle activity”.2 It is associated with several clinical features such as exaggerated tendon reflexes, clasp-knife response and the appearance of pathological reflexes.1 This condition is associated with various complications such as falls, pain, pressure ulcers, etc.3 It is a disorder that mainly affects the anti-gravity muscles, so that in the upper limb the shoulder adductors, elbow, wrist and finger flexors, as well as the pronators of the forearm are usually affected. On the other hand, in the lower limb, the elevated muscle tone characteristic of spasticity predominates in the hip adductors, knee flexors, plantar flexors and inverters of the foot.1 Muscle tone in spasticity is related to the speed of movement, so the faster the stretch, the greater the resistance offered by the body segment.1 The consequences of spasticity range from a physical to a psycho-social aspect, so it hampers hygiene, sexual ability and other activities of daily living.1

On the other hand, strength training, refers to a specialised method of conditioning, which involves the progressive use of a wide range of resistive loads and a variety of training modalities designed to enhance health, fitness, and sports.4 It has been shown that well-programmed strength exercise can improve muscular strength, power, neuromuscular function, mobility, physical functionality and the performance of activities of daily living. It can also prevent falls, increase psychosocial well-being and preserve functional independence.5

The presence of spasticity and its severity have been linked to poor motor function.6-10 Current evidence suggests that the correct management of spasticity may improve motor function.11 Historically, spasticity was mainly treated with passive techniques as therapists suspected that active exercise might increase the condition.12 But this paradigm is changing due to growing scientific evidence that strength exercise appears to have no adverse effects on spasticity,12-17 and could be very beneficial for this patient profile, due to the benefits outlined above. Nevertheless, it is a difficult condition to address and the evidence for treatments is still limited. More research is needed on the management of the various treatments for spasticity.1 Therefore, the aim of this review was to analyse the effects of intervention with strength exercises and different muscle activations on spasticity, strength or function.

A literature search was conducted in February 2020 for publications registered in the MEDLINE, CINAHL and Scopus databases. The terms used in the search were the Medical Subject Headings (MeSH) descriptors “Muscle Spasticity” and “Resistance Training” as well as “spasticity” and “strength” as keywords. The search equations for each database are recorded in Table 1.

For the selection of results, they were filtered on the basis of certain inclusion and exclusion criteria set out in Table 2. The article selection process is also detailed in Fig. 1.

Fig. 1.

Article selection process.

(0.37MB).

To measure the methodological quality of the selected articles, the Jadad scale18 was applied. The results of this scale are detailed in Table 3.

The review process concluded with 10 valid results. The characteristics of these are shown in Tables 4 and 5.

The intervention and results of each article reviewed are detailed below:

In the study by Zhang et al.19, both groups performed strength exercises with the same frequency and volume, i.e. 40 minutes per session, 5 times per week for 8 weeks. The aquatic group (AG) used water resistance for their exercises and the land-based group (LG) performed similar exercises but out of the water. The LG significantly improved knee flexion strength (p=0.035) and ankle dorsiflexion strength (p=0.042) compared to the pre-intervention measurement. On the other hand, the AG significantly improved strength in both knee flexion and extension movements (p=0.027 and 0.000 respectively) and in ankle plantiflexion and dorsiflexion (p=0.014 and p=0.036 respectively), that is to say, in all movements where they measured. The co-contraction ratio in knee extension also decreased in the AG, both compared to the first measurement and compared to the LG (p=0.000). The functional ambulation category (FAC) improved significantly in both groups, from 3 to 3.5 points in the LG (p=0.005) and from 3 to 4 points in the AG (p=0.004). The same is true for the Barthel Index (BI), whose score increased from 65 to 75 in the LG (p=0.000) and from 65 to 80 in the AG (p=0.000). This difference between groups was significant (p=0.009 in FAC and p=0.024 in BI). Spasticity, measured with the modified Ashworth scale (MAS) was not altered in either group.

In the trial conducted by Jung et al.20 both groups performed the same training, which consisted of squatting at the edge of a stretcher for 15 minutes, with the paretic leg further back than the healthy leg. This intervention was repeated 5 times a week for 6 weeks. In addition, they received one hour daily, also 5 days a week of conventional therapy. Prior to the above training, the experimental group (EG) received half an hour of TENS on the peroneal nerve at minimum sensory threshold. The control group (CG) had the electrodes placed but no current applied.

Patients in both groups improved significantly on all variables. The EG improved significantly more than the CG in spasticity, decreasing their score on the Composite Spasticity Score (CSS) from 11.5 points to 8.9 points (p=0.000), while the CG only improved from 11.9 to 10.8 points. There were also significant differences between groups, with the CG improving more in eyes open (p=0.013) and eyes closed (p=0.017) balance and hip strength (p=0.000).

Yang et al.21 conducted a study whose intervention consisted of 20 minutes of active contractions with the application of neuromuscular electrostimulation (NMES). One group trained the dorsal flexors, placing the electrodes on the tibialis anterior (TA) and another group trained the plantar flexors, placing the electrodes on the medial gastrocnemius (MG). After the contractions, they did 15 minutes of walking. This intervention was performed 3 times a week for 7 weeks. On the other hand, the CG received 20 minutes of stretching and passive and active mobilisations, followed by 15 minutes of walking.

The MG group had greater stride length in both legs (p=0.011 in the affected leg and p=0.028 in the healthy leg) compared to the pre-intervention measurement, but did not achieve greater strength in the plantar flexors. The TA group, on the other hand, achieved greater stride length of the affected leg (p=0.036), increased dorsiflexor strength (p=0.012), reduced MAS score from 2.4 to 1.5 points on average (p=0.028) and decreased spasticity index (p=0.025) compared to the pre-intervention measurement. This group also achieved significantly greater active plantar flexion during the toe-off phase of gait (p=0.015) and greater dorsiflexor strength (p=0.009) compared to the CG. The TA group's reduction in spasticity index was significantly lower compared to the MG group (p<0.05).

In the research carried out by Simpson et al.22, the intervention consisted of a warm-up with 1 minute of multiple dorsal flexions followed by 5 contractions at 50% of maximal voluntary contraction (MVC). During the main part of the training they performed 4 sets of 5 repetitions at maximum effort, in which they held each isometric contraction for 5 seconds on the healthy side. Between repetitions they rested for 5 seconds and between sets they rested for 3 minutes. The mirror strength training (MST) group performed the same training, but facing the mirror, strategically placed to look like the affected leg. The training was performed 3 times a week for 4 weeks.

Spasticity was significantly reduced (p<0.05) in all lower limb joints in both groups, from 1.64 to 1.14 at the hip, from 1.63 to 0.90 at the knee and from 1.83 to 1.07 at the ankle in the MAS in the strength training (ST) group and from 1.50 to 1.13 at the hip, from 1.50 to 0.73 at the knee and from 1.80 to 1.22 at the ankle in the MST group. The MST group achieved higher scores on the 10 meter Walking Test (10mWT) (p=0.000) and the London Handicap Scale (LHS) (p=0.030) compared to the pre-intervention measurement. There was no significant increase in strength of either limb in either group. There were no significant differences between groups in any of the variables measured.

In the study by Fernández-Gonzalo et al.23, the EG performed flywheel resistance training based on eccentric overload. They executed a leg-press exercise, completing 4 sets of 7 repetition maximums (RM). They rested 3 minutes between sets. The total volume resulted in less than 2 minutes of contraction per session. The intervention lasted for 12 weeks. The CG continued with their daily routine.

The results indicated that in the EG there were significant strength gains (p<0.05) in both the affected leg, which was the one they trained, and the healthy leg. The CG had a significant deterioration in the Berg Balance Scale (BBS), from 45.6 to 44 points. However, the EG improved significantly on this scale, increasing their score from 42.5 to 45.9 on average. The EG also achieved a significant improvement in the Timed Up & Go (TUG) test, from 20.3 seconds to 18.2 seconds. Spasticity was not significantly altered.

Bye et al.24 conducted a study in which the experimental group limbs performed 4 sets of 10RM. The intervention was performed 3 times a week for 12 weeks. The first two sets were isometric contractions and the last two sets were concentric contractions. The therapists exercised manual and maximal resistance in both isometric and concentric contractions. In case the physiotherapist did not have enough strength to resist, an external weight combined with manual resistance was applied. Both limbs received usual care, including walking, activities of daily living (ADLs) and if deemed appropriate by the therapists, treatments for pain, spasticity or contractures.

The authors had hypothesised that strength training would have no effect due to the patients' poor nerve conduction, however, strength increased significantly. The patients' perception of function and strength was measured on a 15-point scale where -7 means a change for the worse and 7 means a change for the better, through 0, which means no change. The perception was significantly increased compared to the control limb in both function (4.5 points for the EG and 2.4 points for the CG) and strength (4.7 points for the EG and 2.6 points for the CG). Spasticity did not increase or decrease significantly.

In the study that was conducted by Qi et al.25, the CG received NMES on the dorsal flexors for 20 minutes at motor threshold. They performed this 5 times a week for 6 weeks. The EG performed squats 10 times a day, for 2 minutes each time they did them. They also performed unspecified weight-bearing exercise, as well as walking up and down stairs.

Both groups improved significantly on every variable (p<0.05), but the improvement was significantly greater in the EG compared to the CG. The EG improved functionality on the Gross Motor Function Measure (GMFM) increasing the score from 44 to 70.6 on average. Gait speed also increased significantly compared to CG and spasticity decreased significantly from 12 points to 7.6 on the CSS.

Coote et al.26 conducted a trial in which both groups received the same training. This consisted of 6 lower limb exercises, which were squats, heel raises, step-ups, side-stepping, knee extensions and quadriceps contractions in the supine position. In all of them, weight was progressively added. They also progressed in volume, increasing from 1 set of 12 repetitions to 3 sets of 12 repetitions per exercise. They trained 2 days per week for the first 6 weeks and 3 days per week for the last 6 weeks, so the training lasted 12 weeks. The difference between groups was that the NMES group performed 4 of the 6 exercises with electrostimulation: squats, step-ups, knee extensions and quadriceps contractions in the supine position.

No significant differences were achieved between groups, but both groups obtained strength gains in hip extensors (progressive resistance training group (PRT); p=0.034 and NMES; p=0.019). Only the NMES group had gains in quadriceps strength (p<0.05) compared to the pre-intervention measurement and a significantly higher BBS score (p<0.001), increasing their score from 40 to 46 points. The PRT group also increased their score on this scale, starting with 38.5 and ending with 46.5 but this difference was not significant (p=0.059). In terms of TUG, the NMES group decreased from 21.1 to 18.1 seconds, but this difference was not significant, as was that of the PRT group, which decreased from 20.2 to 16.1 seconds. Spasticity with the visual analogue scale (VAS) remained without significant differences (PRT; p=1 and NMES; p=0.083).

Gillett et al.27 conducted a study in which the experimental group underwent strength training consisting of five lower limb exercises with progressively increasing load. After the strength training, they received functional anaerobic training of high-intensity activities such as stair climbing, directional changes and jumping over obstacles. The strength training volume was 70% of the total session. This intervention was performed 3 times a week for 12 weeks. The control group, on the other hand, did their normal daily activities.

In their hypothesis, the authors indicated that the subjects would gain strength and functional capacity. They significantly gained strength in the plantar flexors (p=0.025) but not in the dorsal flexors (p=0.088) compared to the CG. They also significantly improved, compared to the CG, in the Muscle Power Sprint Test (MPST) (p=0.026), in the “10×5m Agility Shuttle” test (p=0.016) and in the “6 Minutes Walking Test” (6MWT) (p=0.006), increasing the distance covered from 500.35 to 530.91 metres.

In the research conducted by Schranz et al.28, the PRT group performed progressive overload strength training consisting of 5 lower limb exercises. These exercises were adapted squats, heel raises, lunges, glute bridge and the lateral step-up. They performed 3 sets of 10 to 12 repetitions.

They also did a warm-up and a cool-down. On the first day, they calculated the 10RM in order to plan a good progressive overload. The high-intensity circuit training group (HICT) performed the same exercises as the PRT group but at a higher speed, without rest and as many repetitions as they were able. Both groups performed 3 sessions per week for 8 weeks.

The HICT group achieved significantly greater strength gains compared to the first measurement, but not compared to the PRT group (p=0.126). The HICT group significantly increased its MPST score compared to the PRT group. However, this latter one significantly improved the Timed Stairs Test (TST) over the HICT group (p=0.006). There were no significant changes in the 6MWT, as the distance increased very little in both groups, but the PRT group managed to significantly improve their TUG time from the first measurement, from 12.6 to 10.8 seconds. Both groups significantly improved functionality, although the PRT group scored significantly higher in functional tests such as TUG (p=0.05), decreasing the execution time from 10.3 to 9.1 seconds and TST (p=0.003). However, the HICT group achieved significant strength gains (p<0.05) compared to the EFP group.

It can be concluded that strength training has no adverse effects on spasticity and it is advisable for this population to practice it due to its multiple benefits.

On the other hand, it must be taken into account that there is little standardisation in the measurement of the different variables. Therefore, it would be imprudent to draw strong conclusions about strength and functional gains in these patients. However, studying the results under caution, it seems that strength training and muscle activation increase strength gains in patients with spasticity, so that it could improve the functionality of these people. However, the current evidence is not yet conclusive about all the benefits that patients with spasticity might gain from strength training, so further research is needed to reach more firm conclusions.