PINCIVERO, D. M., R. M. CAMPY, and A. J. COELHO. Knee Flexor Torque and Perceived Exertion: A Gender and Reliability Analysis. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1720–1726, 2003.
Purpose: The objectives of the present study were to examine gender differences and between-day variability of isometric hamstring muscle peak torque and perceived exertion.
Methods: Subjects included 20 healthy, college-aged male (N = 10) and female (N = 10) volunteers. Each subject completed five maximal voluntary isometric hamstring muscle contractions (MVC), in a prone position, with their knee at 30° flexion. Subjects then completed, in random order, isometric contractions at 10, 20, 30, 40, 50, 60, 70, 80, and 90% of their three highest averaged MVC. Perceived exertion was measured with a modified Borg CR-10 scale after each contraction. Ten randomly chosen subjects were asked to return approximately 1 wk after the initial evaluation to repeat the same procedure. Peak hamstring muscle torque was examined in absolute (N·m), relative (N·m·kg−1), and allometric-scaled (N·m·kg−n) units. Perceived exertion across the contraction intensities was modeled to a power function in order to determine the exponent and proportionality constant.
Results: Males generated significantly greater hamstring muscle torque than females in absolute, relative, and allometric-scaled units (P < 0.05). No significant differences in perceived exertion occurred across the submaximal contraction intensities between females and males, nor for the derived exponents and proportionality constants. Perceived exertion ratings were observed to be significantly lower (P < 0.05) across the contraction intensity range on the second day.
Conclusions: The major findings demonstrated that perceived exertion did not differ between healthy young female and male adults, despite males generating significantly more hamstring muscle torque, and perceived exertion ratings decreased at similar relative contraction intensity levels across testing days.
When voluntary muscle contractions are performed, subjective feelings of perceptual effort arise and, when expressed verbally and measured, is considered to be a rating of perceived exertion. From a practical perspective, these subjective ratings possess significant clinical usefulness and have, therefore, been the subject of much examination. Investigations of the perceived exertion response during resistance-type exercise, or single-joint muscle contractions, have recently increased (11,16–19,21,27). Thus far, two emerging issues, specific to perceived exertion during these types of exercise activities, have yet to be resolved: 1) the possibility of a gender-specific perceived exertion response and 2) day-to-day variability of the response. Currently, many investigations have demonstrated no significant gender differences for ratings of perceived exertion during resistance-type exercise (4,18,21,22,27). However, a recent study suggested that a gender-specific response may exist (16). With respect to day-to-day variability of perceived exertion ratings during resistance-type exercise, recent studies suggest good reproducibility while performing a muscle fatiguing task (4,5). However, little data are available addressing repeatability of the perceived exertion response during nonfatiguing contractions, across a range of different lifting loads.
The hamstring muscle group is composed of four distinct muscles (semimembranosus, semitendinosus, and biceps femoris long head and short head) that receive innervation from the tibial and common peroneal portions of the sciatic nerve originating at spinal levels L4–S3 (8). Functioning primarily as a knee flexor and hip extensor (15), the hamstring muscles have also been hypothesized to play a major role in maintaining dynamic knee stability during functional weight-bearing tasks (26). Some investigations have subsequently attempted to apply this hypothesized role as a mechanism explaining successful restoration of knee function after injury or as a factor explaining the relatively higher incidence of knee injury in female athletes, as compared with males (7). As a functional examination of this muscle group is very complex during weight-bearing exercise activities, it is prudent to demonstrate characteristics of hamstring muscle function (i.e., voluntary strength and perceptual sensations) during isolated contractions. Furthermore, exploring gender differences in voluntary torque production is complicated by different body sizes among individuals. Specifically, allometric modeling is a body mass correction approach that considers the observed relation between body mass and torque production, and has demonstrated that males are able to generate greater values than females (13,22,23).
The relation between incremented voluntary muscle contraction and perceived exertion has been observed to follow a linear (18,21) or nonlinear (22) pattern for the quadriceps femoris muscle group. Given the hypothetical role of the hamstring muscle as a dynamic knee stabilizer (26), the perceptual awareness of effort related to isolated contractions of this muscle group has yet to be investigated. The perceptual “sensitivity” to voluntary increases in hamstring muscle function may provide important insight to rehabilitation strategies subsequent to knee injury. Therefore, the purposes of this study were to examine gender differences and between-day variability of isometric hamstring muscle peak torque, and perceived exertion during incremented contraction intensities. For the present study, it was hypothesized that: 1) no gender differences in the perceived exertion response during voluntary isometric hamstring muscle contractions would occur across incremented contraction intensities (4,18,21,27); 2) repeatability of ratings of perceived exertion would be high between two separate testing days, based on highly reliable torque measures observed previously (30); and 3) males will generate significantly greater voluntary hamstring muscle torque than females, when corrected for body mass (12,13,20).