Influence of Local Cooling on Proprioceptive Acuity in the Quadriceps Muscle

Abstract

OBJECTIVE: To test the influence of cooling on proprioceptive acuity as reflected in the ability to discriminate weights. DESIGN AND SETTING: Participants were trained to perform a weight-discrimination task. Their ability to correctly report small increments in weight was compared before and after local cooling (a 20-minute application of a crushed-ice pack) of the quadriceps muscle group. Data were collected at a university research laboratory. SUBJECTS: Twenty young, physically active adults (undergraduate students; 14 men, 6 women; mean age, 22.1 +/- 2.6 years). MEASUREMENTS: We calculated overall performance in the weight-discrimination task (percentage of discrimination correct) for each participant to estimate the differential threshold (ie, minimal increment in weight that yields a probability of 75% correct responses). RESULTS: Before local cooling, participants discriminated increments in the order of 4% to 10% from the standard weight (mean threshold, 0.17 +/- 0.06 kg). After local cooling, the discriminative performance remained, on average, very similar to that seen before cooling (mean threshold, 0.17 +/- 0.08 kg; paired t test: t = 0.24, P =.81). Only a small group of participants (n = 5) showed evidence of a decreased ability to discriminate weight after cooling. CONCLUSIONS: The perception of force signals required for weight discrimination does not appear to be affected by local cooling of the quadriceps muscle group. This finding provides additional evidence for the relative safety of cold applications and their effect on proprioceptive perceptual abilities.

Figure 1

The participant's starting position on the exercise table with the 0.50-kg increment weight on the lever. Note that the standard weight corresponded to the weight of the lever unloaded (2.50 kg).

Figure 2

Protocol used for weight discrimination. S_w indicates standard weight (2.50 kg), which corresponded to the weight of the lever unloaded. C_w indicates comparison weights (0.50-, 0.40-, 0.28-, and 0.11-kg increments) that were added separately to the standard (lever) to increase its mass. Note that the comparison weight was always the same within a block of trials and that the blocks were presented in an overall sequence of increasing difficulty (ie, first block, 0.50 kg; second block, 0.40 kg; third block, 0.28 kg; and fourth block, 0.11 kg).

Figure 3

Performance in the weight-discrimination task before and after cooling. Each value represents the mean performance of all participants (n = 20) for each increment in weight with the associated SD in one direction. The dotted line indicates the 75% correct discrimination level, which corresponds by convention to the differential threshold.

Figure 4

An individual whose discriminative performance was affected after cooling. The representation is similar to the representation in Figure 3