Downloaded from http://journals.lww.com/acsm-msse by BhDMf5ePHKbH4TTImqenVAHxkFJp/XpPk1L/H3vMGwqMxG9jwOd8eJPG+b4DlKuAX44qu/vwzmc= on 07/29/2018 Perceived submaximal force production in young adult males and females ALLEN W. JACKSON and ROD K. DISHMAN University of North Texas; and University of Georgia, Athens ABSTRACT JACKSON, A. W. and R. K. DISHMAN. Perceived submaximal force production in young adult males and females. Med. Sci. Sports Exerc., Vol. 32, No. 3, pp. 448 – 451, 2000. Clinical treatment in physical rehabilitation routinely uses perceived relative forces. Purpose: This study used psychophysical methods to quantify subjects’ errors during submaximal muscular force production. Methods: A sample of young adult (aged 23  3 yr) females (N = 60, 62  14 kg) and males (N = 50, 72  13 kg) performed a chest press on a hydraulic dynamometer with which they were unfamiliar. In four consecutive presses with a 2-min rest interval between each press, the subjects were asked to produce a force in the order of 25%, 50%, 75% of their maximal force, and a final maximal press. Pilot data (N = 10) indicated good reliability (r xx  0.80) for the protocol. Results: The rs between perceived force production and the desired production were 0.76 (P  0.001) for males and 0.75 (P  0.001) for females. The exponent for the power function between the perceived and desired forces was 1.12 for males and 1.03 for females. The total error ranged from 2.82 kgm (males) to 1.22 kgm (females). The rs and the logarithmic matching of perceived and desired force indicated a linear relationship that is consistent with Borg’s range model, which has proposed that perceptual intensities of force for different people are approximately set equal at a subjective maximum. Conclusion: Many young healthy subjects can produce relative muscular forces with good accuracy. However, some subjects will provide very inaccurate forces that might affect outcomes in rehabilitation or physical training. Key Words: PERCEIVED FORCE, PERCEIVED EFFORT, ERRORS IN FORCE PRODUCTION I t is a common practice in physical rehabilitation medi- cine to ask patients to produce muscular forces relative to a perceived maximal effort. Clinical judgments about treatment and outcome are based on the forces produced by the patient. We were surprised that we could locate only two studies that examined the ability of adults to accurately perceive and produce relative muscular forces during com- mon maneuvers involving limb movements (8,15). Studies from the field of psychophysics indicate that people should be able to perform such forces accurately. In 1892, classical ratio-setting techniques were first used by Fullerton and Cattell (9) to determine whether men could produce a handgrip force that was twice or one-half of a standard force. Later, Stevens and Mack (21) used magni- tude estimation and production tasks to establish that per- ceived force during handgrip contractions grew exponen- tially, with power exponents ranging from 1.7 to 2.0. Relatively few psychophysical studies of force production have been conducted since those early studies, but they have confirmed that perceived force grows according to a power function with the exponent ranging from about 1.4 to 1.7 during thumb opposition (5), handgrip (7,20), and leg or arm cranking on a cycle ergometer (2,3,4,6). Those studies in- dicate that the perception of increments in muscular force grows exponentially, consistent with Steven’s power law that “equal stimulus ratios yield equal response ratios” (19). It is not possible to directly compare people’s perceptions of force derived from ratio setting methods because a com- mon absolute level has not been established; each person judges the magnitude of different forces relative to a per- sonal standard. Nonetheless, Borg’s (1) range principle that perceptual intensities of force for different people are ap- proximately set equal at a subjective maximum, can be extended to predict that people who have had common experiences with resistance forces should be able to accu- rately produce forces representing equal ratios of their per- ceived maximal force. That prediction has been confirmed in a study of incremental leg ergometer cycling in which a power exponent of 1.5 was obtained when subjects esti- mated the degree of effort “in percent of an imagined maximal exertion in the same type of work” (3). An exten- sion of that finding to physical rehabilitation medicine in- volves the comparison of forces produced by people based on proportions of their perceived maximal forces with actual relative forces to determine whether the forces produced are accurate enough for clinical purposes. Using this approach with two small groups (N = 5) of men and women, Cooper et al. (8) reported that the growth of percent perceived effort versus percent maximal force of voluntary contractions of the adductor pollicis during thumb opposition and the quadriceps femoris during static and dynamic extension of the knee was linear, with a slope 0195-9131/00/3202-0448/0 MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2000 by the American College of Sports Medicine Submitted for publication October 1998. Accepted for publication February 1999. 448