Both the Baseline dynamometer and vigorimeter are common clinical instruments for measuring grip strength. However, the vigorimeter measures a pressure, which is fundamentally a different measurement than those obtained with either the Baseline or MAP dynamometers. Although both the Baseline and MAP measure force, the MAP dynamometer is also able to quantify shear forces and force directions. If both instruments were grasped with the same hand geometry, the MAP, which measures both normal and shear forces, would register a greater grip force due to vector summation. However, the results of this study indicate that the participants can produce more force with the Baseline dynamometer. When grasping the Baseline, the fingers are able to curl around the handles. Alternately, when grasping a cylinder (like the MAP), the fingers are more extended and in a less biomechanically-friendly position. This results in the decreased magnitude of measured grip forces observed in this study.
In the current study, the MAP measures of peak force (Peakmax
) and plateau force (Plateaumax
) all demonstrated very high reliability. The plateau phase of the grasp has been referred to as “sustained strength” in other publications.30
Although there is not consensus on whether peak or plateau force is more reliable, several studies examining both have found the peak measure of force to be more consistent than plateau force.30–32
As both measures in this study had very high reliability, either would be an appropriate measure with the MAP dynamometer. From a force magnitude standpoint, the measure of plateau force averaged 73% that of peak force. This agrees well with results from Svensson et al.,30
in which the plateau force averaged between 75–76% of the peak force. Regardless if peak or plateau (sustained) strength is used, both measures have been shown to be repeatable. In comparison, standard clinical instruments like the Jamar, Baseline or Vigorimeter only measure the peak force of the exertion and information on the plateau phase of grip is unavailable.
Another disagreement exists when considering whether to use the average grip force13, 33
of two or three repetitions or the repetition with the greatest grip force31, 34
for analysis. The results of the current study indicate that the repetition with the greatest peak force was significantly greater (~6%) than the average force of the three repetitions. This finding is consistent with that of Langerstrom and Nordgren,31
which found one-repetition maximums averaged 4–5% greater than the average of three repetitions. Both methods have demonstrated very high repeatability in the current study. Other studies have concurrently examined both methods and have also demonstrated the repeatability of both.9, 31
These findings stress the importance of stating which method is used in the analysis as both are valid and repeatable but the difference in force is approximately 4–6%.
The MAP dynamometer examined in the current study has reliability and validity consistent with other devices currently used in clinical and research settings, when testing both young participants and community dwelling older adults. This is important as evidence indicates the older adult population may have greater relative variability in grip force.2
In addition, similar differences in grip strength were observed between young participants and community dwelling older adults regardless of device. The benefit of the new device is that information about the way hands produce force can be obtained from each trial. The grip profile can be dissected to reveal information on grip force vectors, force build-up, peak force, plateau force, force variability and time to reach fatigue
Unlike the Baseline dynamometer, the MAP captures the force vectors involved in gripping. This information is important because results from Amis35
indicate that shear forces are a sizable portion of the overall grip force. Devices that only measure the scalar magnitude are unable to quantify the shear forces involved in gripping. Additionally, the MAP dynamometer can estimate the finger contributions involved in the grip27
which can help clinicians or researchers determine whether individual fingers are not contributing to the grip. As a whole, these data available from the MAP dynamometer have clinical and research importance. By understanding which components of grip strength are most affected, targeted interventions can be developed to address the specific deficits. The limitations of the MAP dynamometer include its current lack of commercial availability and the cost due to specialized fabrication and instrumentation techniques. However, the MAP provides a more comprehensive evaluation of the function of the hand than is available from standard devices.