Essential tremor (ET) is a neurological disorder characterized by involuntary and rhythmic shaking. Typically, tremors occur in upper extremities such as the hands but tremors can exist in other body parts as well (Mayo Clinic, Aug 2017). Individuals suffering from essential tremor experience disturbances and difficulties in completing everyday tasks such as feeding and handling / manipulating small objects such as scissors, keys etc. Essential tremor is more prominent in individuals over 40 years of age and typically worsens over time.
Clearly, the disturbances caused by essential tremor have the potential to be disruptive and frustrating. While there are current pharmacological treatments available, some individuals have persistent symptoms. As such, alternative forms of therapy have been a topic of research in recent years.
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Effects Of Resistance Training
Research conducted by Kavanagh, Wedderburn-Bissop and Keogh (2016) examined the effects of resistance training (RT) on essential tremor. The aim of their research was to determine whether a 6-week resistance training intervention could help remediate symptoms of essential tremor. In order to do this, they recruited individuals with essential tremor and a healthy, age-matched control group. They hypothesized that the resistance training intervention would create positive changes in manual dexterity and reduction of tremor force in individuals with ET. They also predicted that individuals with essential tremor would have greater improvements compared to the healthy control.
The resistance training intervention involved three key exercises including bicep curls, wrist flexion, and wrist extension. All exercises were performed with dumbbells and all exercises were performed on both the most affected limb and the least affected limb (as essential tremor often impacts one limb more than the other). For each participant, the researchers established a “5RM”, that is, a dumbbell weight for which the participants could complete 5, but no more, repetitions. This was used to gauge strength and the exercise sessions were adjusted so that throughout the intervention, all participants were utilizing weight that was a certain percentage of his or her 5RM weight.
- Bicep Curl
- Wrist Flexion
- Wrist Extension
Throughout the 6-week intervention, participants attended supervised exercise sessions 2x a week for 45-55 minutes. All sessions began with a warmup. The first set of the session utilized a weight that was between 40-50% of the participants 5RM. For example, if their 5RM weight was 25lbs, the first session utilized a dumbbell weight between 10-12lbs. The next three sets had increased intensity and utilized weights that could only be lifted for 8-10 repetitions. If a subject was able to complete 10 repetitions in each set, the load was increased by 1kg for their next session.
Measures of functional assessment were obtained pre and post intervention. The researchers utilized four key clinical measures of upper limb function and manual dexterity including:
- PPT: measured fine manual dexterity by placing a maximum number of small pins in a vertical column on a board within a 30 second period
- Nine-Hole Peg Test (9HPT): nine larger wooden pegs are inserted into a board and then removed as quickly as possible
- Modified Moberg Pick Up Test (MMT): tested with eyes closed, eyes open, and with eyes closed which naming each object they were manipulating
- Modified Jebsen Hand Function Test (MJHFT): subtests administered measured page turning ability and eating activities
In order to measure the force of the tremor, they utilized a model of measurement employed by Kenway, Bisset and Kavanagh (2014) to identify maximum voluntary contraction (MVC). Below, is an image of the device used to measure tremor. Participants were instructed to place his or her palm on a custom designed device which measured index finger abduction force.
- The resistance training intervention successfully reduced tremor amplitude for the ET group for the most affected limb.
- Individuals with essential tremor demonstrated greater improvements in strength (measured by 5RM) for bicep curls, wrist extensions, and wrist flexion compared to healthy older adults.
- The resistance training intervention successfully contributed to improvements in manual dexterity as measured by the MMT. Individuals with ET demonstrated significant improvements in both the most affected limb and the least affected limb.
- The ET group had greater improvement in dexterity. The ET group improved performance on 7/10 subtests whereas the healthy control improved performance on 4/10 subtests.
- After the intervention, there was a significant improvement in measures of eating ability (involving controlling a spoon) for the most affected limb for the ET group as well as the healthy control group.
According to the researchers, the improvement is likely associated with improving functioning that declines with normal aging as opposed to targeting the movement dysfunction associated with ET particularly (Kavanagh, p 28). Either way, the important takeaway is that the improvements in dexterity and strength were observed for individuals with ET.
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Future research should explore the role of cardiorespiratory fitness to improvements in dexterity, strength, and tremor symptoms. The present study utilized a measure of strength (5RM) but there was no measure of cardiopulmonary fitness. It would be interested to investigate whether individuals with higher levels of cardio pulmonary fitness prior to the intervention demonstrated greater or fewer improvements in dexterity, strength and symptom reduction.
Additionally, future research should investigate the effects of resistance training from a preventative perspective. That is, can the introduction of resistance training at the first signs of ET help slow down the progression of essential tremor?
Finally, it would be interesting to investigate how combining forms of exercise may improve force tremor. Understanding the positive effects associated with cardiovascular exercise, it would be worthwhile to examine if an exercise program combining resistance and aerobic training produced added benefits to dexterity and symptom reduction.
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Essential Tremor, MayoClinic, Aug 2017, retrieved on December 5th 2017 from https://www.mayoclinic.org/diseases-conditions/essential-tremor/symptoms-causes/syc-20350534
Kaveanagh, J.J., Wedderburn-Bissop, J., Keogh, J.W.L. (2016) Resistance training reduces force tremor and improves manual dexterity in older individuals with essential tremor. Journal of Motor Behavior, 48:1, 20-30.
Kenway, L. C., Bisset, L. M., & Kavanagh, J. J. (2014). The effect of isometric contraction on the regulation of force tremor in the contralateral limb. Neuroscience Letters, 558, 126–131.