Isometric Hand Grip Strength Measured by the Nintendo Wii Balance Board

A Reliable New Method

A. W. Blomkvist; S. Andersen; E. D. de Bruin; M. G. Jorgensen


BMC Musculoskelet Disord. 2016;17(56) 

In This Article



Following the guidelines for reporting reliability and agreement studies (GRRAS),[22] we tested the intra-rater reproducibility of the WBB performing tests one week apart. Concurrent validity was also explored by comparing the WBB to JD on the first session. Participants were randomized to start with either the WBB or JD in order to avoid order effects.


Thirty older adults were recruited using the member lists from senior citizen clubs and organizations in Aalborg, Denmark. Using telephone interview, participants were included if they were 65 years or more, willing and able to come to the hospital twice within a week by themselves, and able to pass a small custom dementia screening (correctly answering the current year, month and prime minister of Denmark). Participants were excluded if they had acute illness within the previous 3 weeks, orthopaedic surgery on upper or lower limbs within 6 months or neurologic disease (e.g. Parkinson's disease, severe dementia). All participants gave written consent and the study was approved by the regional ethics committee, The North Denmark Region Committee on Health Research Ethics, which is appointed by The Regional Council of the North Denmark Region.

Overall Experimental and Calibration Procedures

Participant characteristics such as height, weight, handedness, number of drugs taken and physical activity in hours per week were obtained prior to testing. All tests were performed at the same time-of-day, in the same clinical examination room at Aalborg University Hospital and by the same rater. The rater was a trained physiologist (MGJ). Devices were calibrated by applying known weights of 0.2, 0.5, 1.0, 1.5, 2, 4, 5, 8, 10, 20, 30 and 50 kg to the force transducers.


WBB is a rigid square-shaped platform with four uni-axial vertial stain gauge transducers in the corners. Using Bluetooth HID wireless and custom programs written in C#, data was streamed to a computer (Lenovo Yoga Pro, Windows 8). The software recorded the isometric force-time curve from the sensor values reported as four channels of 16-bit digital data samples at approximately 100 Hz and subsequently filtered using a 4th order Butterworth filter (cut-off frequency 20 Hz). The resulting accuracy of the software is 100 gram on the whole measurement range (from 0 to 300 kg).

Before starting the actual tests, participants received a set of standard instructions and demonstration of the procedure. Afterwards they were seated in a standard chair (seating height 43 cm), which was used for all tests. Participants were then asked to hold the WBB with their left and right hand around the middle of the WBB with the lower face of the board towards their torso. All tests were initiated with the right hand, which held and squeezed the upper right corner. This was followed by the left hand holding and squeezing the upper left corner, as illustrated in Fig. 1. Prior to the actual testing, 2–3 sub-maximal recordings were performed. This served both as habituation and warm-up. After the warm-up, the actual tests were performed with a total of three measurements per hand alternating between right and left hand. The participants were encouraged to squeeze as long and as tightly as possible until a plateau had been reached. This took about 3–5 seconds and was visualized on the monitor which both the examiner and participant could see. The examiner instructed the participant when to stop. The participants rested their hands for 15 seconds before the next measurement.

Figure 1.

Demonstration of a left hand grip strength measurement by pressing the upper left corner of the Nintendo Wii balance board


The JD (Lafayette Instruments Company, USA) is the most widely cited dynamometer in the literature and it is accepted as the gold standard by which other dynamometers are evaluated. It reads force in both kilograms and pounds, with markings at intervals of 2 kg. According to our calibration procedures, the JD required a minimum of 2 kg to make the manometer move, which may be inappropriate when measuring very weak patients. Accordingly, it has been reported that the measurement error of the JD is greater at lower loadings.[23]

Similar to the WBB test, participants received a set of standard instructions for the procedure followed by a demonstration. They performed 2–3 sub-maximal recordings prior to actual testing. In addition, participants rested their arm on a standard table (height 71 cm) with the JD initially in the right hand followed by the left hand. The hand was positioned with the thumb on one side of the handle, while the other fingers were on the other side (see Fig. 2). The handle was set to position no 2. Similar to the WBB, a total of three measurements per hand were completed and the participants were encouraged to squeeze as long and tight as possible until a plateau had been reached.

Figure 2.

Demonstration of a left hand grip strength measurement by pressing the Jamar handdynamometer


Data are presented as mean ± standard deviation (SD), and all statistical analyses were performed using SPSS (version 22). The dominant and non-dominant hands were analysed separately and measurements were presented as first measurement, mean of two measurements, mean of three measurements and highest value out of three measurements. For reproducibility, the difference between session one and two (for WBB) was tested for normal distribution both statistically (Shapiro-Wilk) and visually (histogram). Further, the difference between each participant's individual score from the mean of the measurements in both sessions was plotted in a simple scatter plot for signs of heteroscedasticity.[24] Paired t test was used to explore systematic bias between sessions. For relative reproducibility, intra-class correlation coefficient (ICC) was calculated with a 95 % confidence intervals[25] using absolute agreement in a two-way mixed model, and the results of a single measurement was reported. The ICCs were interpreted based on the recommended ranges of poor (<0.69), fair (0.70–0.79), good (0.80–0.89), and high (0.90–1.00) for both relative reproducibility and validity.[26] For absolute reproducibility, the standard error of measurement (SEM) and limits of agreement (LOA) was calculated using the SD of the participants difference score between the two session multiplied by and 1.96, respectively.[27] The absolute values were also presented as percentages by dividing SEM and LOA with the mean value of all participants for both sessions.

For validity, Pearson's product–moment correlation between WBB and JD from session one were calculated for the first measurement, mean of two measurements, mean of three measurements and highest value of all three measurements. The correlations were interpreted as high (>0.70), moderate (0.50–0.69), low (0.26–0.49), and absent (0.00–0.25).[26] To further support the validity analysis we included a calculation of ICC using a two-way mixed consistency model and reporting results of a single measurement.