Elsevier

Journal of Hand Therapy

Volume 24, Issue 1, January–March 2011, Pages 22-30
Journal of Hand Therapy

Scientific/Clinical Article
Using the Force–Time Curve to Determine Sincerity of Effort in People with Upper Extremity Injuries

https://doi.org/10.1016/j.jht.2010.07.005Get rights and content

Abstract

This was a prospective cohort study. In a previous study, the slopes of the force–time (F–T) curve were shown to differentiate between maximal and submaximal grip effort in healthy participants. The objective of the study was to examine if the slopes of the F–T curve can determine the sincerity of effort in people with upper extremity injuries. Forty participants with unilateral upper extremity injury performed maximal and submaximal grip efforts. The F–T curve was recorded, and the slopes of the force-generation and force-decay phases were calculated. Repeated-measures analysis of variance revealed significantly steeper slopes for maximal than those for submaximal efforts. However, receiver operating characteristic curves showed that, at best, the slope of the force-generation phase yielded overall error rates of 55% for women and 60% for men. Therefore, sensitivity and specificity values were insufficient to effectively differentiate maximal from submaximal efforts. The slopes of the F–T curve did not validly measure the sincerity of effort in participants with upper extremity injury, perhaps, because they were protective of their injured hand and, thus, exerted only submaximal effort even at their best grip attempt.

Level of Evidence

Not applicable.

Section snippets

Participants

Forty participants with current upper extremity injuries (20 men and 20 women) were recruited from various hand therapy and rehabilitation clinics in North-Central Florida. The sample size was estimated based on a power analysis of data from a previous study using healthy participants.1 Physical and occupational therapists identified and recruited patients who met the study criteria. Inclusion criteria were 1) age between 18 and 65 years and 2) treated for unilateral upper extremity injuries

Results

Demographic and injury-related data are summarized in Table 1. The average values of the F–T curve slopes are found in Table 2. The slopes of force-generation phase were significantly steeper for maximal effort when compared with submaximal effort [F (1, 38) = 55.77, p  0.0001], uninjured hand when compared with injured hand [F (1, 38) = 9.44, p  0.004], and men compared with women [F (1, 38) = 7.61, p  0.009] (Table 3, Figure 2). Similarly, the slopes of force-decay phase were significantly steeper for

Discussion

The slopes of the force-generation and force-decay phases of the F–T curve were found to be valid in determining the sincerity of effort in healthy people.1 The purpose of this study was to examine if these slopes can validly distinguish between maximal and submaximal grip efforts among people with upper extremity injuries. A valid sincerity-of-effort test should reveal significant differences between maximal and submaximal efforts, and indeed, we found significant differences for the slopes of

Conclusions

The significantly steeper slopes for maximal efforts when compared with submaximal efforts indicated that the slopes of the force-generation and force-decay phases of the F–T curve can differentiate between maximal and submaximal efforts in people with upper extremity injury. However, sensitivity and specificity values were insufficient to effectively differentiate maximal from submaximal efforts, perhaps, because participants were protective of their injured hand and, thus, exerted only

Acknowledgment

This work was supported in part by the Evelyn Mackin Research Grant of the American Society of Hand Therapists. Partial equipment support was provided by Thought Technology Ltd., Montreal, Quebec, Canada.

Quiz: Article #174

Record your answers on the Return Answer Form found on the tear-out coupon at the back of this issue or to complete online and use a credit card, go to JHTReadforCredit.com. There is only one best answer for each question.

  • #1.

    According to the motor unit recruitment model, maximal effort

    • a.

      cannot be approximated

    • b.

      requires synchronous firing of all motor units

    • c.

      requires simultaneous and maximal activation of all motor units

    • d.

      does not result in fatigue of motor units

  • #2.

    The slope of the force-decay phase of a

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