Exercise as it relates to Disease/The effects of progressive resistance training on individuals with Down Syndrome

This is a critique of the article by Patrick M. Cowley, Lori L. Ploutz-Snyder, Tracy Baynard, Kevin S. Heffernan, Sae Young Jae, Sharon Hsu, Miyoung Lee, Kenneth H. Pitetti, Michael P. Reiman & Bo Fernhall (2011) The effect of progressive resistance training on leg strength, aerobic capacity and functional tasks of daily living in persons with Down syndrome, Disability and Rehabilitation, vol. 33:22-23, pp. 2229-2236

What is the background to this research?
Down syndrome (DS) is a developmental disability resulting from an extra copy of a chromosome. Individuals with DS also present hypotonia, muscle weakness and low aerobic capacity which can lead to impairments in physical function and limit functional ability resulting in loss of independence, increased need for services and support and decreased quality of life.

In this article, it mentions that the cause of muscle weakness in individuals with DS is still unknown. Although, it does address the research question by testing the hypothesis that progressive training would increase isometric and isokinetic knee extensor and flexor strength, peak aerobic capacity and increase walking speed.

Individuals with DS are more likely to perform labour jobs such as filling boxes, carrying, standing and their ability to perform these jobs could become impaired if any further losses in strength occur with ageing. Therefore, it is important to address these issues related to these individuals.

Where is the research from?
Thirty individuals with DS participated in this study and all individuals had been diagnosed with DS and mild intellectual disability by a medical professional and this was confirmed by the parent and/or guardian.

The author of this article, Patrick M. Cowley, is a PhD at Syracuse University in San Francisco. Patrick has over 30 research items dating from 2005 to 2019. After this article, a study offered new insights on the cause of muscle weakness in DS individuals where Patrick Cowley was the lead researcher.

What kind of research was this?
This research is a non-randomised controlled trial to test the hypothesis with an intervention and control group.

Many studies show similar evidence of progressive resistance training improving lower limb strength. Such as data from, shows that progressive training was effective in improving the strength of the major antigravity muscles of the lower limb (quadriceps and hip extensors) in adolescents with DS. The average percentage increase in muscle strength was 42% which suggests that it is clinically worthwhile.

What did the research involve?
There were four tests that the thirty participants completed; progressive resistance training program, knee extensor and flexor isometric and isokinetic strength, functional tasks of daily living and peak aerobic capacity. Progressive resistance: This included three sets of 8-10 repetitions of leg extensions and flexion, leg press, shoulder press, chest press, bicep curl and tricep pushdowns that was performed using machines 2 days per week for 10 weeks. At the start of the program, the participants were familiarised with the exercises and how to properly use the machines. Each participant worked one-on-one with an exercise professional who supervised all training sessions. The weight was lifted recorded and was progressively increased to consistently load the muscle. Knee extensor and flexor isometric and isokinetic strength: Participants were positioned in the dynamometer where maximal isometric peak torque was obtained by having the participant perform three sets of maximal contractions with the knee extensors and flexors at a joint angle of 45, 60 and 75 degrees. Maximal isokinetic peak torque was obtained by having the participant perform three sets of five maximal contractions with knee extensors and flexors at 60 degrees/sec with 3 minutes between sets. Functional tasks of daily living: Each participant was timed on their ability to perform functional tasks of daily living as fast as comfortable as possible, which included the time to rise from a chair with varying heights. For stair ascent, participants were asked to ascend 10 stairs as quickly as possible without using the hand railing for support. They were asked to walk one step at a time and one leg after the other. Walk speed was determined by having the participant walk 7.62m as fast as possible without running. Walk speed was calculated by dividing the distance travelled by time. Peak aerobic capacity: Each participant performed a test of peak aerobic capacity on a treadmill using an individualised protocol. The speed was first adjusted to a fast walk and every 2 minutes the grade was increased by 2.5% until a maximum grade of 12.5% was reached. At this point, the speed of the treadmill was increased every minute by 1.61km/h until participants could no longer keep up or showed volitional exhaustion.

Three sites in the USA were chosen as an intervention and control group and this was based on the capability to provide supervised intervention. This method is selection bias which strays away from being random. Although, pre and post-testing method were performed by the same investigators.

The biggest limitation of this study was selection bias due to the non-randomised controlled trial. Participants were assigned to a control or intervention group and were not randomised. Another limitation is the uneven size of the intervention and control group. There was also a small number of female participants in the study which could have prevented an examination of sex differences in the training response.

What were the basic results?
The results for isokinetic measures showed that the intervention group exhibited a greater increase in knee extensor and flexor peak torque compared to the control group. For the isometric measure of strength showed that the intervention group exhibited a greater increase in knee extensor peak torque but not knee flexor compared to the control group. For the chair rise time, the intervention group exhibited a decrease in the absolute change in stair ascent and descent. For aerobic capacity, the intervention group exhibited an increase in the absolute change in the respiratory exchange ratio.

Results interpreted that isometric knee flexor strength did not change with training due to it being highly angle specific and participants did not perform isometric contractions with knee flexors at the angles tested during training. However, the increase in isokinetic strength is likely due to the resistance training mirroring the type of testing. Results suggest that improving leg strength can positively impact functional tasks such as ascending and descending stairs. However, improving leg strength does not affect aerobic capacity. This might be due to the program not having a sufficient number of training days and low training stimulus.

Implications of the research findings were mentioned and their reasons why were also mentioned which suggests that they are aware of the improvements they need to make in later studies.

What conclusions can we take from this research?
The conclusion states that further investigations should examine the effect of progressive resistance training in adults with DS where functional becomes very limited and becomes an indicator of mortality, in which I do agree due to the increased level of evidence the data will have. The participants' age in this study ranged from 20-30 years old where functional abilities could still be increasing. Data from this article suggest that individuals with DS have 80% reaching the third decade and 60% living beyond fifty. Furthermore, I do believe that progressive resistance training and other healthy lifestyles should be implemented into individuals with DS at an early age so they can be healthy going into old age.

A recent article (2017) conducted a randomised controlled trial with 31 children with DS to investigate the effects of isokinetic training on muscle strength and postural balance. Results suggest that the children who participated in the isokinetic training program displayed greater improvements in muscle strength and postural balance.

A more recent article (2018) conducted a 4-week high amplitude standard exercise program on 8 adults with DS that were recruited from a residential facility. Results displayed that there was an increase in self-selected gait speed but it did not have a significant effect on their balance or functional strength. This result suggests that there is a minimum amount of time where improvements in functional strength will be visible in individuals with DS.

Practical advice
This research did have exclusion criteria which included:
 * 1) Any contraindications to exercise
 * 2) Severe or profound intellectual disability
 * 3) Documented atherosclerotic heart disease
 * 4) Documented atlantoaxial instability
 * 5) Uncorrected congenital heart disease
 * 6) Implanted prosthetic device
 * 7) Implanted pacemaker
 * 8) Musculoskeletal disorders preventing participants from successfully completing any of the tests
 * 9) Less than 16 years of age

Other types of real-world implications were not mentioned.

Further information/resources
After this article was published, an article was shortly published providing new insights on the cause of muscle weakness in individuals with DS which was conducted using mice as a control group.

This website article is very informative and can offer a lot of support to families of individuals with DS and medical professionals.

This website can offer support and reliable information to parents who have or expecting a child with DS. Information is constantly being updated and reviewed which can ensure that the information is latest.