asymmetries in knee extension strength do not ...

ASYMMETRIES IN KNEE EXTENSION STRENGTH DO NOT CORRELATE WITH SAGITTAL PLANE KNEE LANDING MECHANICS IN RESISTANCE TRAINED MEN Jakob Rosengarten  Jose A. Arevalo  Scott K. Lynn  Jennifer A. Spencer  Lee E. Brown FNSCA  Pablo B. Costa  Andrew J. Galpin Center for Sport Performance, Department of Kinesiology, California State University, Fullerton

ABSTRACT

PURPOSE

Poor landing mechanics are often a result of weak lower body musculature. Yet, no study has compared knee-landing mechanics from a drop vertical jump to knee extension strength. In addition, no study has examined these variables in relation to leg dominance. METHODS: Sixteen resistance-trained men (age=23.94±2.9yrs; height=180.19±6.4cm; mass=85.23±10.7kg; mean±SD) volunteered. The men were asked to perform six drop vertical jumps (i.e., step off of a 31cm box, land, and perform a vertical jump as quickly as possible) onto two side-by-side force plates embedded into the ground. In random order, participants were instructed to step-off the box with either the right foot first (three trials) or the left foot first (three trials), land, and jump using both feet. The dominant leg was categorized as the preferred “kicking leg”. Peak sagittal knee moment and peak vertical ground reaction force (VGRF) was measured for each leg. Maximal jump height was measured bilaterally using Visual 3D biomechanical program. Following the jumps, participants were asked to perform one-repetition maximum(1RM) knee extension for each leg. RESULTS: Paired Samples T-Tests showed a significant difference in knee extension strength between the dominant (64.2±11.0kg) and non-dominant (61.1±9.1kg) legs (p=0.036). However, asymmetries did not exist between legs sagittal knee moment (p>0.05) or VGRF (p>0.05). Moreover, no significant correlations were found between bilateral vertical jump height (49.6±9.9cm), knee extension strength (for dominant r=0.013 or non-dominant r=-0.067), sagittal knee moment (for dominant r=0.301 or nondominant r=0.211), and VGRF (for dominant r=0.067 or non-dominant r=-0.064). Thus, we combined values for the left and right leg for VGRF and sagittal knee moment. No correlation was observed between jump height and combined VGRF (1.91±0.4xBW, r=0.005), and combined sagittal knee moment (2.22±0.4Nm/kg; r=0.265). Furthermore, no correlation was observed between bilateral sum strength (left+right leg 1RM) (125.3±21.3kg), jump height (r=-0.039), VGRF (r=0.286), and sagittal knee moment (r=0.019). CONCLUSIONS: Asymmetries in strength between limbs is not uncommon, particularly in untrained populations. Surprisingly, we report differences in maximal strength between limbs in previously leg strength trained men. The “preferred kicking leg” functioned as an appropriate question for the establishment of leg dominance (strength) among this cohort. We hypothesized these functional differences among limbs would yield asymmetries in drop jump performance. However, our data indicate strength differences cannot predict landing mechanics or leg dominance among strength-trained men. The differences in muscle action between the 1RM test (singlejoint, concentric only) and the drop jump (multi-joint, eccentric followed by concentric) may explain our findings. Future investigations should examine more similar strength tests such as a 1RM squat.

Examine the relationship between landing mechanics, knee extension strength, and leg dominance in resistance trained men

RESULTS Table 1: Paired Samples T-Test of knee strength, sagittal knee moment, and vertical ground reaction force (VGRF) between legs. * = Statistically Significant Table 2: Individual and combined descriptive statistics and correlations with jump height Dominant vs. Non-Dominant Legs

METHODS

1RM Knee Extension Sagittal Knee Moment VGRF

BOX DROP VERTICAL JUMP

1RM KNEE EXTENSION

p = 0.03* p > 0.05 p > 0.05

Dominant Leg Knee Extension Strength Non- Dominant Leg Knee Extension Strength Bilateral Sum Knee extension Strength Dominant Leg Sagittal Knee Moment Non- Dominant Leg Sagittal Knee Moment Combined Sagittal Knee Moment Dominant Leg VGRF Non-Dominant Leg VGRF Combined VGRF

Mean ± SD

Correlation with Jump Height

64.2±11.0kg 61.1±9.1kg 125.3±21.3kg 2.23±0.262 Nm/kg 2.24±0.395 Nm/kg 2.22±0.4 Nm/kg 1.936±0.469 xBW 1.887±0.544 xBW 1.91±0.4 xBW

r=-0.013 r=-0.067 r=-0.039 r=0.301 r=0.211 r=0.265 r=0.067 r=-0.064 r=-0.005

CONCLUSION  

Dominant “kicking” leg strength > Non-Dominant leg strength No relationship between leg dominance, strength, and landing

PRACTICAL APPLICATION  

Significant differences in single joint strength may not necessarily predict movement mechanics during complex, multi-joint activities in resistance-trained men. Injury screening tests and tools should understand this limitation when implementing. The use of such a test to predict asymmetries in jump performance (and therefore, predict the likelihood of future injury) is questionable in this group of participants.