The primary reason to take multiple measurements is to limit the likelihood of regression to the mean. This phenomenon occurs when a person has an unusual high (low) value and then on the next measurement the value is much closer to the overall mean. This is a result of within-individual variation, but it happens within groups as well. So by taking several measurements (and in this case average them together), you are reducing that variability and thus limiting the probability that the change from pre to post-intervention is a function of regression to the mean rather than a treatment effect.

I am not sure how short of time frame you'll need to go with for multiple baseline measurements. One can argue that taking too many hand-grip measurements too close together would cause fatigue which would result in continuously reduced strength. On the other hand, taking the measurements over two or three days may introduce other reasons why the measurements would not be consistent. So I would probably go with 3 measurements over the course of a single day, with sufficient rest between measurements to ensure complete recovery.

I am attaching a paper on regression the the mean. I think it may be important for you to read.

Ariel

Article Assessing regression to the mean effects in health care initiatives

The primary reason to take multiple measurements is to limit the likelihood of regression to the mean. This phenomenon occurs when a person has an unusual high (low) value and then on the next measurement the value is much closer to the overall mean. This is a result of within-individual variation, but it happens within groups as well. So by taking several measurements (and in this case average them together), you are reducing that variability and thus limiting the probability that the change from pre to post-intervention is a function of regression to the mean rather than a treatment effect.

I am not sure how short of time frame you'll need to go with for multiple baseline measurements. One can argue that taking too many hand-grip measurements too close together would cause fatigue which would result in continuously reduced strength. On the other hand, taking the measurements over two or three days may introduce other reasons why the measurements would not be consistent. So I would probably go with 3 measurements over the course of a single day, with sufficient rest between measurements to ensure complete recovery.

I am attaching a paper on regression the the mean. I think it may be important for you to read.

Ariel

Article Assessing regression to the mean effects in health care initiatives

Dear Hao Chen

I have some experience with this type of test, so sending you the following suggestion.

As well remembered by colleague Ariel Linden, one of the reasons of repeating a same test is to prevent one of the major threats to the ecological validity: the phenomenon of statistical regression. Indeed, this is one of the reasons for the test of grip strength, is accomplished with three tries. However, there is consensus on the fact that the results of a test, especially when the assessed are not familiar with it, will be more valid if the test is repeated two or more times (usually one day). Additionally, the repetition of the test a second time, will allow you to evaluate the repeatability coefficient, thus ensuring better psychometric qualities, valuing the results.

I would like to thank our colleague Ariel the excellent reference.

Amandio

Grip strength measurement in general has high test-retest reliability on intra-rater, inter-rater, trial-to-trial, and day-to-day differences among various populations. For two repeated measurements, reliability can be indicated by Pearson correlation coefficient or Bland-and-Altman plot. For multiple repeated measurements, it can be indicated by coefficient of variation, standard error of measurements, or intraclass correlation coefficient (ICC).

The followings are some examples studying the reliability of day-to-day variation in grip strength measurement:

 My recommendation is that if you cannot find literature studying the reliability of grip strength measurements on population with physical characteristics similar to the subjects of your interest, it may be necessary to run your own study, especially if the subjects have some unite physical characteristics. Most of the times we do not measure grip strength on separate days. To ensure good validity and reliability, we calibrate the dynamometer with known weights over the range of measurement periodically and strictly follow the standard method of measurement (ASHT, 1992; Roberts et al., 2011). We measure grip strength 3 times separated by at least one minute of rest. If possible, a sub-sample is tested within 2 weeks to establish our day-to-day reliability.

Comparison of grip strength should be cautious because our experience and others (Amaral et al., 2012) indicate that strength may be significantly different when measured by dynamometers of different manufacturers. Whether the highest or the average value of several trials is taken from dominant or non-dominant hand should also be noted in comparison across studies even using the same type of grip dynamometer.

Furthermore, reporting as “maximum strength” is redundant because muscle strength is defined as “a muscle group can exert against a resistance in one maximum effort” (Fox et al., 1988), “the maximum force a muscle or a muscle group can generate” (Wilmore and Costill, 1994), or “the amount of force that a muscle can produce with a single maximum effort” (Brooks et al., 2000). The readings recorded on a dynamometer can be a result of maximal or submaximal contraction so muscle strength may also be expressed as maximum muscle force or tension.

References

Amaral et al. (2012) Rev Bras Fisioter, 16(3): 216-24.

ASHT (1992) Clinical Assessment Recommendations.

Brooks et al. (2000) Exercise Physiology, p.424.

Desrosiers et al. (1993) CJOT, 60(1): 9-16.

Fox et al. (1988) The Physiological Basis for Exercise and Sport, p.160.

Kamimura and Ikuta (2001) J Rehabil Med, 33: 225-9.

Molenaar et al. (2008) J Bone Joint Surg Am, 90: 1053-9.

Roberts et al. (2011) Age and Ageing, 40: 423-9.

Schaubert and Bohannon (2005) J Strength Cond Res, 19(3): 717-20.

Wilmore and Costill (1994) Physiology of Sport and Exercise, p.68.

Thanks so much for all of your kind suggestions and informative explanations.

Because our assessed mice were injected with some drug before test, in addition to the reliability problem which is important, some researcher needs to check if there is any fluctuation of motor function during recovery after injection. So I recently realized that might be part of the reason why a series of tests over days was suggested. Based on your responce and literature, most people may not test for that long.

It will take me some time to digest the kindly provided references.

Hao

I would recommend the following simple suggestions:

Prior to testing your treated mice, ensure that the individual testing grip strength is well trained to do so consistently. I would recommend a trial run where testing is done several times in one day and then over multiple days. There can be a lot of variability in animal and operator performance. This will help you determine problems such as fatiguability and animal learning.

I found that with repeated testing, my rats were able to learn how to perform the grip strength task better and showed improvements attributed to learning rather than the intervention. It may be that you find over consecutive days of testing that the mice reach a plateau in performance which is often the best point to determine whether an intervention further improves performance.

I would consider reading as much as possible about different testing protocols and trying them yourself first. I am somewhat sceptical of those who do a single day of testing prior to and after an intervention as I found significant variability in normal/untreated rats using this protocol. I therefore opted for multiple tests in one day and then repeating this over several days.

Apologies if this answer is not as sophisticated as the above!