Introduction
The 30-second Chair Stand Test is a useful clinical test to estimate someone’s leg strength and endurance time-efficiently. However, the construct validity of the 30-second Chair Stand Test was poor according to Tolk et al. (2019), since it does not directly evaluate muscle strength or power.This is because these characteristics must be stated in Newtons (N) and Watts (W), respectively (Gill et al., 2022). It would be better to calculate the power from the number of repetitions since it increases the validity of the test and may be a more clinically relevant outcome. Let me take you through these calculations!
How to Calculate Power from the 30-s CST?
Muscle power refers to the capacity to produce strength as fast as possible. To calculate the muscle Sit-to-Stand (STS) power produced, the following formula was derived by Alcazar et al., 2018 and 2020:
From the STS power, we can calculate relative power by dividing it by the participants’ weight. We can also calculate the allometric power, by dividing the STS power by someone’s height squared. The allometric power is normalized to body composition.
How does the Physiotutors team perform?
We gathered this information from our team, let’s see how we scored!
- Max performed 37 reps in 30 seconds on a chair height of 0,45m. He weighs 73kg and is 1.74m tall.
- Arjan did 29 reps on a 0.44m chair. He weighs 64kg and is 1.74m tall.
- Andreas did 19 reps on a 0,47m chair. He weighs 89kg and is 1.83m tall.
- Steve managed to do 22 reps on a 0.46m chair. He is 1.83m tall and weighs 77kg.
- Ellen did 25 reps on a 0.45m chair. She weighs 79kg and is 1.73m tall.
Mixing these values in the formulas gives us the following results:
- Max achieved the highest power with 668,4 Watts, followed by Ellen achieving 482 Watts, Arjan achieving 470 Watts, Steve with 454,9 Watts, and Andreas with 443,2 Watts.
- When looking at the relative power, Max is our top scorer achieving 9.16 Watts per kilogram. Arjan achieved 7.34 W/kg, Ellen 6.10 W/kg, Steve 5.91 W/kg and Andreas 4.98 W/kg.
- The allometric power was 220.6 W/m2 for Max, 161 W/m2 for Ellen, 155 W/m2 for Arjan, 135.8 W/m2 for Steve, and 132,3 W/m2 for Andreas.
What do these values mean?
The relative power is the mean STS power, adjusted by body mass. The allometric muscle power is adjusted by height squared. These scaling methods are necessary to compare strength measures across individuals with different body sizes.
For example, looking at our results above, I “finished” third in the number of repetitions performed. Yet, I produced the second-best power output with 482 Watts. However, the relative power revealed my third place again.
Jaric in 2002 stated that “Even the basic athletic, clinical, or everyday life experience suggests that taller or heavier individuals are usually stronger than the shorter and lighter ones. This effect becomes particularly prominent when animals of similar body stature, but very different sizes are compared.”
When the relative power was calculated, my score was corrected for my body weight. Then I was ranked third again. Here you can see that my body weight made me stronger than I really was, at least theoretically. Since I weigh 15kg more than Arjan, but we are of approximately the same height, correcting for my weight was necessary to compare our results.
This can also be used to compare strength values intra-individually. For example, in middle-aged and older people, it was found that relative muscle power declined to a greater extent than other power-related parameters (Coelho-Júnior et al., 2023). Such declines were accompanied by significant increases in body mass and body mass index (BMI). Sarcopenia is an age-related decline in muscle mass and strength. People lose muscle mass, but on the other hand, people tend to gain weight (by an increase in fat), especially after menopause in women. As such, their BMI might stay relatively constant. The relative muscle power takes body mass into account since it is calculated by dividing the yielded power by the participant’s weight. Hence, you can take into account changes in power when somebody loses muscle mass despite staying relatively constant in their weight (and thus BMI).
Also here, this applied to my score. Generally speaking, women have more body fat than men. In our Physiotutors team comparison, I certainly have more body fat than Arjan. When my Power output was corrected for my body mass, it revealed that I had produced less power than Arjan.
What is the Accuracy of this test?
The relative sit-to-stand power is reliable as it demonstrated an area under the curve (AUC) of 0.85 in women and 0.89 in men in the receiver operator characteristic curve (Alcazar et al., 2021).
Precautions/Standardizations
Standing up from a lower chair means sitting in more flexion in the lower extremities, which requires a bigger maximal moment of the knee joint. Therefore, the power equation includes the height of the chair.
Practical implications
A variation of this test is the 5-times Sit-to-Stand (STS) Test. However, it is better to calculate the power from the number of repetitions performed in 30 seconds since it increases the validity of the test and may be a more clinically relevant outcome. In case you did measure the 5-repetition Chair Stand test instead of the 30-second Chair Stand Test, you can use the formulas below (Alcazar et al., 2018):
The 30-second Chair Stand Test and 5-repetition Sit-to-Stand test are strongly correlated, yet may measure different physical constructs. Yee et al. (2021) found that the 30-second Chair Stand Test requires more cardiorespiratory endurance, while the 5-repetition sit-to-stand test is more relying on dynamic balance.
How much power do you minimally need to be able to rise from a chair?
Alcazar et al. (2021) studied this topic and categorized it according to the participant’s height and how the test was performed. The height was grouped into deciles on the horizontal axis:
- Shorter than or measuring 1.47m
- 1.48m-1.49m
- 1.50m-1.52m
- 1.53m-1.55m
- 1.56m-1.58m
- 1.59m-1.60m
- 1.61m-1.63m
- 1.64m-1.67m
- 1.68m-1.73m
- Greater than or equal to 1.74m
For someone like me, who is in the 9th decile (as I measure 1.73m), to be able to perform at least 5 repetitions in the 30-second Chair Stand Test, I would need at least 1.21 W/kg of relative muscle power. With my score of 6.1 W/kg, I am doing good.
Furthermore, they found that when someone does not reach at least 5 repetitions on this 30-second test, the prevalence of mobility limitations and disability in basic and instrumental activities of daily living is significantly higher than in someone who successfully reached the 5-repetition threshold during the 30-second Chair Stand Test. Assessing sit-to-stand performance and calculating power is crucial to monitoring older people and defining who is at risk!
Normative data
As aging affects the performance of individuals on this test, it is recommended that you compare your patient’s result to normative values. It is important to use relative muscle power to compare your patient’s results to his peers of the same age and gender. The normative values have been studied by Alcazar et al., 2021 (see tables below).
Normative data for younger and older individuals
Normative data for older women and men (from 60 years of age and older)
The table here lets you categorize someone’s performance on the 30-second Chair Stand Test according to his peers.
The cut-off point for low relative muscle power was 2.1 W/kg in older women (AUC [95% CI] = 0.85 [0.84–0.87]; sensitivity = 73.7% and specificity = 86.0%) and 2.6 W/kg in older men (AUC [95% CI] = 0.89 [0.87–0.91]; sensitivity = 79.0% and specificity = 86.6%).
What does the evidence tell us about specific interventions for improving sit-to-stand power?
Lizama-Pérez et al. (2023) investigated the effects of sit-to-stand (STS) training on muscle quality in sedentary adults. To conduct the study, the researchers divided the participants into three groups: one group performed 3 sets of 5 repetitions of the sit-to-stand exercise, another group performed 3 sets of 10 repetitions three times per week for 8 weeks, and a third group served as a control group and did not participate in the exercises. The researchers measured muscle architecture and muscle function before and after the training period. Muscle architecture refers to the structure and arrangement of muscle fibers, while muscle function refers to how well the muscles can perform tasks.
The researchers found that both the 5-repetition and 10-repetition STS training programs had positive effects on muscle architecture and muscle function in sedentary adults, compared to the control group which did not improve. This means that the sit-to-stand exercise helped improve the overall health and function of the muscles in the participants.
In simpler terms, the study showed that doing sit-to-stand exercises can make your muscles stronger and healthier, even if you are not very active. So, incorporating this type of exercise into your routine can be beneficial for improving muscle quality.
Bao et al. (2020) found from their meta-analysis that exercise programs showed overall significant positive effects on muscle strength and physical performance but not on muscle mass in sarcopenic older adults. We know that muscle mass declines gradually over the years, starting from our 30-ies. Strength training was found to reduce the time needed to perform 5 Chair stands.
Furthermore, Alcazar et al. (2021) established an algorithm to determine what specific type of intervention would be necessary to improve people presenting with suboptimal muscle functioning. For example, if you encounter a male person with a low relative power and a BMI above 28 kg/m2, this person should be helped to decrease body fat. This is not only because of the extra weight but also due to the increased inflammatory impact of fat accumulation on muscle function.
Part B of this algorithm can only be followed in case you have access to a body composition analysis through Bioelectrical impedance analysis or DXA scan. Specific muscle power refers to the power the legs can produce to complete the sit-to-stand test. Here, the exact weight of the legs should be used to calculate the specific power.
What is the minimal amount of improvement that is clinically important?
Previous evidence by Wright et al., (2011) found a change of at least 2 repetitions in the 30-second Chair Stand Test a minimally clinically important difference. Alcazar et al., (2021) found that this minimally clinically important difference of 2 repetitions is related to a difference of 0.33 watts per kilogram in women and 0.42 watts per kilogram in males.
Conclusion
Because of its low time, space, and material requirements, the 30-second chair stand test is an excellent option for use in clinical settings. In 30 seconds of performing the test and in a few minutes doing the math, you can have a relevant measure of somebody’s muscle functioning, which you can compare to his peers. With the use of the algorithm, you can determine the need for specific interventions and by using the same test, you can track progress over time.
