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North American Congress on Biomechanics Canadian Society for Biomechanics - American Society of Biomechanics University of Waterloo Waterloo, Ontario, Canada August 14-18, 1998 |
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Eight college-age males completed a protocol of maximum isometric actions for knee extension and flexion, plantar flexion, and dorsiflexion. These actions were performed unilaterally with each leg and bilaterally. The knee extensor group was the strongest muscle group with the dorsiflexors the weakest. The muscles acting on the knee showed significant bilateral deficits (BLD) for both extension and flexion as did the ankle plantar flexors. Interestingly the dorsiflexor group showed little evidence of a BLD.
The study of the quadriceps muscle group has been the primary choice of researchers comparing bilateral and unilateral contractions. The advantages of studying this muscle group are numerous but the application of these data is limited. For example, although the knee musculature generates large extensor torques during a sit-to-stand (STS) task the hip extensor moment is larger indicating the relative importance of this movement and its associated musculature (Rodosky et al., 1989). Vander Linden (1994) suggested that dorsiflexion is important early during the STS movement to pull the tibia forward such that the CM is moved over the base of support before extension in the hip/trunk begins providing the stability needed to perform this task. Rodosky et al. (1989) observed distinct asymmetries in the lower limb resultant moments during a STS movement (perhaps due to limb dominance).
These asymmetries combined with the bilateral nature of the STS task suggest that an investigation of the bilateral and unilateral strength characteristics of the lower extremity muscular would be useful. This study compares the strength of the knee and ankle musculature when activated bilaterally and unilaterally. The knee extensors were hypothesized to be the strongest muscle group followed by the knee flexors, plantar flexors, and dorsiflexors, respectively. Each muscle group was hypothesized to demonstrate a bilateral deficit.
Two Cybex II isokinetic dynamometers were employed to provide independent measures of limb strength for each side of the body. Each dynamometer was calibrated prior to each testing session. These dynamometers were interfaced with a Biopac A/D board. Torque measurements were sampled at 1000 Hz for a period not greater than 6 seconds.
Eight college-aged males (24.6 ± 1.8 yrs) provided informed consent prior to participation in the study. Each subject was free of injury to the knee and ankle joints. Testing was completed on two separate occasions in which a single joint, either knee or ankle, was tested. Prior to the strength tests the subjects warmed up by riding a stationary bike for 10 minutes. The subjects were then positioned on the dynamometers.
Conditions were randomized between unilateral left, unilateral right, and bilateral. Three trials were recorded for each condition. Each subject was instructed to develop and maintain a maximal effort for approximately 3 seconds as quickly as possible. Each subject was provided 2-3 minutes of rest between maximal efforts. The knee was positioned at 60° of flexion (0° = full extension) for both flexion and extension tests. The ankle was positioned at 0° plantar flexion (i.e., the foot was perpendicular to the shank) for the plantar flexion test and at 20° plantar flexion for the dorsiflexion test.
The bilateral index was defined as by Howard and Enoka (1991)
such that a negative value indicated a bilateral deficit and a positive number indicated a bilateral facilitation. BLD means were compared using a 4 × 2 ANOVA (joint movement × leg). Mean differences between individual joint movements were assessed using a Student Newman-Keuls post-hoc test.
Torque was normalized to body weight. No significant interaction was found for torque values between joint movement and leg indicating that the data could be collapsed across legs. Knee extensor torques were largest followed by plantar flexor, knee flexor and dorsiflexor torques. Each of these torques was significantly different from the others (p<0.05). No significant interaction was observed for the bilateral index between the joint movement and leg indicating that the data could be collapsed across legs. Ankle plantar flexion, knee extension, and knee flexion all demonstrated bilateral deficits that were not significantly different from each other. Ankle dorsiflexion demonstrated a slight bilateral facilitation which was significantly different from the other three movements (p<0.05).
| Normalized Torque (Nm) |
Bilateral Index (%) |
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|---|---|---|
| Plantar Flexion | 0.179 (0.032) |
-7.6 (8.0) |
| Dorsiflexion | 0.070 (0.005) |
+2.5 (5.5) |
| Knee Flexion | 0.142 (0.035) |
-8.7 (9.6) |
| Knee Extension | 0.245 (0.062) |
-4.4 (14.2) |
Several methodological issues may have impacted these results. The dorsiflexion strength test was the least familiar to the subjects. This may have impacted the ability of the subjects to record a true maximal effort but both the torque measurements and the bilateral indices had the smallest standard deviations. This indicates that these measurements were the most consistent. The large amount of variability associated with the knee extensor, knee flexor, and plantar flexor measurements may be indicative of some subjects becoming fatigued during the testing session.
The bilateral index for knee extension was smaller than those observed by Owings and Grabiner (personal communication, 12/97) but larger than those observed by Häkinnen et al. (1995). As anticipated, knee flexion and plantar flexion movements also demonstrated bilateral deficits. However, dorsiflexion was the only movement that demonstrated a bilateral facilitation. The uniqueness of the dorsiflexor response coupled with its role in such tasks as the STS suggests that further research is warranted into bilateral activation of this muscle group.
Owings, T and Grabiner (personal communication, 12/97)
Häkinnen, K. et al. (1995). Eur. J. Appl. Physiol., 70: 518-527
Howard, J.D. and Enoka. R.M. (1991). J. Appl. Physiol., 70: 306-316.
Rodosky, M.W. et al. (1989). J. Orthop. Res., 7: 266-271.
Vander Linden, D.W. et al. (1994). Arch. Phys. Med. Rehabil., 75: 653-660.