A COMPARISON OF OPEN AND CLOSED CHAIN KNEE EXTENSION EXERCISES ON PATTERNS OF QUADRICEPS HYPERTROPHY

Resistance training causes hypertrophy, however, the magnitude of muscle growth varies along the length of the muscle (i.e. proximo-distally). For running based athletes and those dependent on movement about the hip, preferential proximal hypertrophy of the quadriceps femoris (the primary knee extensor) shifts the center of mass (CoM) of the thigh closer to the hip which provides a direct biomechanical advantage by decreasing the moment of inertia of the high about the hip (I). This in turn can increase movement velocity and economy and has been observed in studies using mathematical modeling and when comparing elite national level sprinters. Recent studies have reported that the pattern of quadriceps hypertrophy differs between different types of training (plyometrics vs traditional heavy resistance training) or when different types of contractions (eccentric vs concentric) are performed. However, no study to date has explored how exercise selection affects patterns of hypertrophy. Therefore, the purpose of the present study was to compare the effects of open kinetic chain (OKC) and closed kinetic chain (CKC) exercises on quadriceps patterns of hypertrophy and to determine if patterns of hypertrophy differ and if so does this result in a significant effect on CoM and I. Given pilot data from our lab, we hypothesized that CKC would result in similar proximal hypertrophy but less distal hypertrophy of the quadriceps compared to OKC, thus shifting CoM proximally and decreasing I about the hip. To test our hypothesis, 12 untrained participants (male =7; female = 5) aged 18-35 years participated in an 8 week resistance training intervention where each participant trained by performing both unilateral CKC (squat) and OKC (knee extension) exercises on separate legs. Before and after the training program MRI of the quadriceps femoris was performed in order to measure changes in muscle cross sectional area in the proximal-thigh (1/3 thigh length), mid-thigh (1/2 thigh length) and distal-thigh (2/3 thigh length). Regional cross sectional area of the quadriceps femoris was compared between exercises and over time using a 2 x 2 mixed model ANOVA with Bonferoni post-hoc corrections. Results revealed that both conditions resulted in an increase in muscle volume which was similar between conditions (CKC Δ 60.2 ± 110.5 cm3, OKC Δ 79.5 ± 87.9 cm3, p = 0.285). However, the pattern of hypertrophy differed along the length of the thigh and between conditions with CKC experiencing a significant increase in cross sectional area in only the distal-thigh region (p = 0.044) and OKC experiencing a significant increase in both the midand distal-thigh regions (p = 0.003-0.004). Additionally, a significant interaction effect of exercise and time was observed for CoM (p < 0.001) and I (p < 0.001), where CKC resulted in CoM shifting proximally and I reducing about the hip when compared to OKC. Given running and other athletes can benefit from a proximal shift in CoM of the thigh and reduced I of the thigh about the hip, our results suggest that running based athletes should preferentially select CKC exercises over OKC exercises during their resistance training program.