STRENGTH CURVE COMPARISONS BETWEEN GENDER FOR SHOULDER INTERNAL AND EXTERNAL ROTATION

Abstract

Development of appropriate strength training protocols for injury rehabilitation is partly dependent on accurate knowledge of the strength curve (SC) exhibited by a muscle group. To date, SCs for the shoulder have not been identified for internal (IR) and external rotation (ER) in the neutral position, nor have differences in gender been examined. PURPOSE To develop SCs for shoulder IR and ER and to compare SCs by gender. METHODS Subjects were 15 males (Age: 22±3 yrs; Ht: 178.5±8.5 cm; Wt: 85.4±17.0 kg) and 15 females (Age: 21±2 yrs; Ht: 168.5±7.5 cm; Wt: 70.1±9.2 kg) SCs were obtained by measuring maximal isometric torque in 15° increments for IR and ER from 30° (maximum ER) to 135° (maximum IR). The upper arm was in anatomical position, the forearm was flexed 90°, and the radioulnar joint was neutral. The 90° position for ER and IR was the position in which the forearm was aligned perpendicular to the frontal plane. To examine SC magnitude differences by gender, a two-way repeated measures ANOVA (Gender X Angle) was calculated for peak torque. To examine SC shape differences by gender, a one-way ANOVA was calculated for the slope of SC between measured angles. RESULTS Significant gender differences were observed in the magnitude and shape of SC for IR and ER. Males had significantly greater absolute torques throughout the ROM in IR and ER, exhibiting 121% greater maximum torque (MT) in IR (MTmales = 54.6±16.0 Nm; MTfemales = 24.7±6.5 Nm) and 94% greater MT in ER (MTmales = 39.6±15.5 Nm; MTfemales = 20.4±3.7 Nm). With regard to shape, no differences were observed in the direction of slopes or in the angle at which peak torque (APT) occurred (APTIR = 60°; APTER = 135°). However, differences in magnitude of slope were observed. Torque decreased at a greater rate for males from 135° to 75° ER ROM (Males = ↓ 16%; Females = ↓ 1%) and from 75° to 135° IR ROM (Males = ↓ 31%; Females = ↓ 19%). CONCLUSION These results indicate that SCs for shoulder IR and ER differ between males and females. Strength training protocols for injury rehabilitation may need to consider these differences.