Strength Training in Neurological Rehabilitation
Original Editor - Mariam Hashem
Strength Training in Evidenceneurological conditions limiting mobility. Resistance training has been found to improve muscle strength and functional performance when added to functional exercises.
A systematic review by Kjølhede in 2012 reported strong evidence regarding progressive resistance training on muscle strength for people with Multiple Sclerosis (MS). A more recent study by Patrocinio de Oliveira and colleagues found that patients with MS had improved knee extensor 1 repetition maximum, Timed 8-Foot Up and Go, Chair Stand Test following progressive resistance training and eccentric strength-enhanced training. However, the authors note that eccentric strength-enhanced training appeared to improve the transfer of strength adaptations to functional tests. Progressive resistance exercises are also strongly recommended by the Australian Stroke Foundation guidelines (2017) and the AHA guidelines (2010), but the optimal strengthening approach is still unknown. Different systematic reviews demonstrated improvement in strength following resistance training, but showed limited impact on walking parameters. A recent randomised controlled trial by Kanegusuku and colleagues found that progressive resistance training can specifically improve cardiovascular autonomic dysfunction in patients with Parkinson's. Williams et al investigated task specificity of strength training for walking in neurological conditionsfandound quadriceps and hamstrings exercises to be the most commonly used exercises in neurological rehabilitation.
Biomechanics of Gait
A good understanding of gait parameters is needed to prescribe proper exercises for walking. Muscle recruitment and speed influence walking mechanics across hip, knee and ankle joints. In older adults, it has been found that a lower walking speeds reduce gait quality. A minimal level of strength is required in all muscles to generate power for walking, however, not all muscles are recruited equally.
Three key events are important for power generation during the walking cycle:
- Hip extensor power generation at Initial Contact
- Ankle plantar flexion power generation at push-off (terminal stance)
- Hip flexor power generation at toe-off to accelerate the leg through the swing phase
At the knee joint, muscles generate force for power absorption:
- Knee extensors at terminal stance
- Knee flexors at terminal swing to decelerated the leg.
At the stance phase, the main power is generated at the ankle, when the plantar flexor generates power at terminal stance for push off. A study analysed the power generated at the ankle joint and found that Achilles tendon produced the highest peak of force. Stance phase makes up about 0.6 seconds of the gait cycle. Push off represents about 0.15 seconds- this is when the achilles tendon is producing most of the power. Strength training can increase the muscle-tendon strength but not the power needed for the push off.
Is It Just About Strength?
Progressive Resistance Exercises (PRE) is a form of power training. Power Training focusses on overcoming resistance but also focusses on the ability to overcome the resistance in the shortest period of time. PRE are considered the best method for improving force production and muscle hypertrophy. Changing resistance constantly is the key to improve strength. Heavy resistance training improves strength whereas ballistic (lighter loads and high repetitions) training improves power generation.
Speed is another factor that influences gait mechanics as muscle power generation during walking occurs at high angular velocities. Applying the principals of ballistic training at a targeted speed at the ankle joint can be the key to improve walking .
A 2017 study evaluated the effect of functional high-velocity resistance training (power-training) to improve muscle strength and walking capacity of children with Cerebral Palsy. Significant improvement was reported in the muscle power sprint test, 1-minute walk test (1MWT), 10-m shuttle run test (SRT), gross motor function, isometric strength of lower-limb muscles and dynamic ankle plantar flexor strength reflecting improvement on walking capacity.
Seated leg press was performed with and without a jump in a single testing session by Williams. A 70% increase in concentric velocity was reported in the ballistic exercise condition.
In Williams et al systematic review, most studies did not include exercises relating to all three main power events important for walking. Instead, strength testing and strengthening exercises were prioritised for the knee extensors and flexors, despite their minor role in normal gait cycle.
Considerations for exercise prescriptions:
- Power training is recommended over conventional strength/resistance training with considerations to gait biomechanics.
- Exercises should be performed with speed
- Exercise has to be specific to the muscles that generate the power (ankle plantar flexor). If the patient is unable to isolate the right muscle, apply some modifications to allow for proper performance.
Task specificity principals based on ACSM guidelines:
- Role of the muscle
- Action of the muscle
- Type of contraction
- Active range and segmental alignment
- Speed of movement
- Progressive muscle overload
- Greater intensity
- Increasing total repetition & training volume
- Increasing the speed of movement
- Reduce rest
- Muscle Endurance
- Sports application
In neurological conditions, proximal compensations greater forces were observed in the hip flexors and extensors. Power training can reverse these proximal compensations. Despite being highly important for standing up from a chair and stairs, quadriceps strengthening is not the key for better walking.
To improve walking and gait focus on ballistic or fast exercises, and particularly target the calf because it is so important for walking. For example, if you have no resources or are in a home environment, it would be better to do a quick 'calf drop' exercise rather than a controlled calf raise – i.e. raise up onto the toes and then quickly drop down and push up again. Or with access to a mini-trampet the exercise could involve bouncing between alternate heel raises demonstrated in the video below.
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