RELATIONSHIP OF STRUCTURAL DIMENSIONS TO LEG PRESS STRENGTH IN TRAINED ADOLESCENT FEMALES
by
David L. Mayhew and Mike Hafertepe
Academy of the Holy Angels High School, Richfield, MN

Original Publication Information:
IAHPERD Journal Volume 29. No.2 Spring, 1996.
INTRODUCTION
Previous research has indicated that muscular strength is related to body size (Mayhew et al., 1991). Much of this research has centered on upper body strength measurement such as the bench press. In those studies, structural dimensions such as muscle circumferences have been relatively successful in predicting one-repetition maximum (1-RM) strength. Only a few studies have attempted to predict the 1-RM squat from structural dimensions (Mayhew et al., 1993). The limited success of these studies may be due to the complex nature of the squat technique.

Of the studies done to estimate strength from size, only a few have used female subjects (Mayhew, et al., 1989; Scanlan et al., 1995). The focus of these studies has been on the bench press and have been done with college-aged females. It would be interesting to determine if structural dimensions could predict leg strength more accurately in the leg press since it may reduce the skill requirement necessary in the squat (Mayhew et al., 1993). Furthermore, could enhanced prediction be accomplished using trained females who may be more capable of reaching their maximum potential? The purpose of this study was to determine the relationship of structural dimensions (anthropometry) to leg press strength in trained adolescent females.

METHODS
Fifteen female members of a high school track team gave their informed consent to serve as subjects. Each was measured for height, weight, hip circumference, thigh circumference, thigh length, and leg length. Hip circumference was taken around the maximum part of the gluteal muscles. Thigh circumference was taken around the right thigh midway between the inguinal fold and the patella with body weight supported on that leg. Thigh length was measured from the greater trochanter to the midline of the knee joint. Leg length was measured from the midline of the knee to the lateral malleolus. Triplicate measurements for circumferences and lengths were averaged for analysis. Total leg length was calculated by adding thigh and leg lengths.

The 1-RM leg strength was measured using a leg press machine. Each subject warmed up using a weight of her choice for 5 to 10 repetitions. After sufficient rest, the subject performed single repetitions until she was unable to extend her legs fully. From 2.2 to 9.9 kg was added for each successive trial. The 1-RM was usually reached in 4 to 7 trials. Each trial was begun in the extended position, and the weight lowered slowly until the knees were flexed at approximately a 90-deg angle. The subject was required to fully extend the knees on each repetition.

RESULTS
The means, SD, and relationship of structural dimensions with leg press are shown in Table 1. Only total leg length and body mass index (BMI = weight (kg)/height2 (m)) had significant relationships to leg press. The remaining correlations were moderate in magnitude accounting for 1.2% to 19.4% of the common variance.

Multiple regression analysis selected total leg length and thigh circumference as the best variables to predict 1-RM leg strength. The multiple R = 0.67 with a standard error of estimate of 20.2 kg. The equation is:

Leg Press (kg) = 424.8 + 2.2 Thigh Cir (cm) -4.2 Total Leg Length (cm)

DISCUSSION
In this limited sample of trained adolescent females, structural dimensions showed slightly greater potential to predict strength than has been indicated in untrained females using a bench press test (Scanlan et al., 1995). This finding might indicate that the neural learning which takes place with resistance training may enhance the potential of females to reach their strength potential (Johnston, Mayhew & Piper, 1993). Indeed, recent research on trained college female athletes noted a higher correlation between structural dimensions and bench press strength than has been shown previously in untrained females (Peterson et al., 1996). In the study by Peterson et al. (1996), the authors noted that females with greater arm muscle circumference and muscle cross-sectional area produced greater 1- RM bench press values. In addition, athletes with lower %fat values also had greater strength. Unfortunately no body fat estimates were made in the current study, but the girls with greater thigh circumference had greater leg press scores.

The relationship of BMI to leg press strength in the current study (Table 1) was higher than the r = 0.40 noted for the college athletes using the bench press (Peterson et al., 1996). This finding would indicate that the shorter female for a given weight would have greater leg strength. This was further supported by the negative relationship between total leg length and leg press: the shorter the leg length, the greater the leg press strength. In addition, the correlation between body weight and leg strength was substantially lower than that noted between body weight and squat performance in college male athletes (r = 0.50)(Mayhew et al., 1993).

Previous research on male athletes has shown that squat strength was more difficult to predict from anthropometric dimensions than was bench press 1- RM (Mayhew et al., 1993). The authors speculated that leg strength measurement procedures may involve more joints and be more difficult to estimate from simple structural dimensions. Perhaps a combination of endurance repetitions and structural dimensions might yield more accurate prediction of leg strength.

In summary, these data indicate that despite isolating the measurement of leg strength by using a leg press machine, it is still more difficult to predict the 1-RM leg strength than it is to estimate bench press strength. Training among adolescent females does appear to enhance the relationship between structure and function as has been shown in college female athletes (Peterson et al., 1996), but prediction may not be of sufficient accuracy to allow its routine use.

r = 0.51 significant at p<0.05.

Table 1. Means, SD, And Relationships Of Structural Dimensions To Leg Press Strength
Variable Mean SD Correlation
Age (y) 16.3 1.2 0.41
Height (cm) 167.9 6.1 - 0.44
Weight (kg) 61.5 4.5 0.16
BMI (Wt/Ht2) 21.9 1.8 0.54
Hip Cir (cm) 96.7 4.1 0.02
Thigh Cir (cm) 50.6 2.6 0.42
Thigh Length (cm) 48.4 3.6 - 0.50
Leg Length (cm) 47.2 2.1 - 0.13
Total Leg Length (cm) 95.7 3.3 - 0.63
Total Leg Length/Ht 0.57 0.01 - 0.22
Leg Press (kg) 138.9 25.1
REFERENCES