Elsevier

Neurotoxicology and Teratology

Volume 25, Issue 5, September–October 2003, Pages 543-553
Neurotoxicology and Teratology

Factors affecting grip strength testing

https://doi.org/10.1016/S0892-0362(03)00073-4Get rights and content

Abstract

The rodent grip strength test was developed decades ago and is a putative measure of muscular strength. This test has been included in the functional observational battery (FOB) to screen for neurobehavioral toxicity, and changes in grip strength have been interpreted as evidence of motor neurotoxicity. Despite its widespread use, questions remain about what the grip strength test actually measures. In this study, potential confounders of the grip strength test were identified and tested, including operational parameters, disruption of peripheral sensory function and changes in body weight. Operational parameters (sampling rate, system type and trial angle but not trial speed) had dramatic effects on grip strength data. Doxorubicin (DX, 10 mg/kg iv) was used to cause sensory impairment. It decreased forelimb and hindlimb grip strength (by 27% and 32%, respectively, compared with controls), an effect that was correlated with degeneration of peripheral and central sensory components (distal tibial and sural nerves, dorsal funiculus of the spinal cord and dorsal, but not ventral, spinal roots). Feed restriction-induced loss of body weight (26% compared with controls) and muscle mass (20% compared with controls) reversibly decreased both forelimb and hindlimb grip strength (18% and 17%, respectively, compared with controls). Ignoring these confounding factors could potentially lead to increased data variability and inconsistency within single studies, across studies and in historical control data sets. To assist in data interpretation and evaluation of grip strength results, it is suggested that exact conditions of application of the test be reported in greater detail. Furthermore, given that the grip strength test can be influenced by factors other than true muscular strength, use of the term grip performance is proposed to better reflect the apical nature of this test.

Introduction

A test for grip strength measurement in rodents was developed more than 20 years ago [2], [14]. It is a behavioral test that was eventually introduced into regulatory test batteries to screen for neurobehavioral toxicity. It became a component of the functional observational battery (FOB) and typically fits under the motor test section [27].

Typically, the grip strength apparatus consists of a grasping device or platform (e.g., grid, ring, T-bar) that is connected to a strain gauge or load cell. In general, the test measurement is conducted by allowing the animal to grasp the device and then pulling it away until its grip is broken. A reading from the strain gauge is recorded. Three such trials are performed and the measurements are usually averaged. Often, no specific instructions are reported in the publications that indicate how practically each test trial was performed.

A potential source of differences in the results of grip strength tests arises from the fact that several types of grip strength devices are commercially available; some have been specially built. The systems that have been described in the literature potentially vary along several dimensions. The platforms the animals grasp can be unsupported or supported at the periphery and may be connected to different types of load cells. The mode of administration of the test varies among technicians and from laboratory to laboratory (even in a laboratory regulated by Good Laboratory Practices), e.g., the execution of the test can vary from a smooth pull to a brisk jerk.

It was also recognized early that there were potential overlaps between different functional domains, e.g., an effect on sensory functions could be expressed as a motor impairment [27]. As far as the grip strength test is concerned, questions can be asked about the role that other factors, such as behavioral, physical and operational, can play in determining the outcome of the grip strength measurement. As stated above, a number of factors can affect the variability of the grip strength measurement. In the present paper, the roles of the following factors in determining the outcome of grip strength testing will be considered: sampling frequency of the load cell, angle at which the animal is pulled, system type (with or without support of the grid platform) and speed of each trial. Additionally, the effect of peripheral sensory function (through doxorubicin (DX)-induced sensory impairment) and body weight loss (through scheduled feeding) on grip strength were examined.

Section snippets

Experimental subjects

Fischer 344 female rats were obtained from Charles River Laboratories (Raleigh, NC). They were allowed to acclimate to our laboratory for 1 week and were evaluated by a laboratory veterinarian who determined their general health status and acceptability for study purpose and who provided veterinary care during the rest of the study. Rats were kept in temperature- and humidity-controlled rooms (24–26 °C and 30–70%, respectively) and were on a 12 h light/dark cycle (lights on at 6:00 a.m. and off

Load cell sampling rate

Grip strength trials collected at sampling rates of 20, 1000 and 5000 Hz were recorded as 426, 718 and 714 g for forelimb and 240, 517 and 560 g for hindlimb, respectively (Fig. 2). The effect of sampling rate on both forelimb (slope=0.041, P=.0008) and hindlimb (slope=0.049, P=.0002) grip strength measurement was significant.

Trial angle and support system

The difference in recorded forelimb grip strength between supported and unsupported systems (Fig. 3) was statistically significant [F(1,76)=18.9, P=.0001]. This effect was

Discussion

The purpose of this study was to identify and study factors that affect grip strength testing. A better understanding of these factors would reduce the chance of incorrectly concluding that apparent treatment-related changes in grip strength are due to adverse effects on the nervous system.

Conclusion

Grip performance is affected by a variety of factors including parametric factors, peripheral sensory nervous system damage and diet restriction-induced changes in body weight and muscle mass. Changes in grip performance due to loss of body weight were reversible and positively correlated with changes in hindlimb muscle mass. Forelimb grip performance was apparently affected differently than hindlimb in the diet restriction study, but no apparent differential effect in either was seen following

Acknowledgements

The authors wish to acknowledge Jennifer A. Murray for her assistance in skillful intravenous injections and data collection, Jonilyn Van Fleet for performing the perfusions as well as tissue and slide preparation, Lisa G. McFadden for statistical analysis and Drs. Joel L. Mattsson and Bernard S. Jortner for critical reading of this manuscript.

References (27)

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