STUDY DESIGN: A case-control study, with single observation. OBJECTIVES: To compare the onset timing and activation of the vastus medialis oblique (VMO) and vastus lateralis (VL) between subjects with and without patellofemoral pain syndrome (PFPS) at various step heights. BACKGROUND: It has been theorized that delayed or reduced VMO activity relative to the VL contributes to lateral patellar tracking and PFPS. However, conflicting evidence exists in the literature regarding this proposed mechanism. The lack of agreement among studies may be attributed to inconsistent knee flexion angles used in previous studies. METHODS AND MEASURES: Twenty subjects with PFPS (mean ± SD age, 29.5 ± 10 yrs) and 20 control subjeccts (mean ± SD age, 25.4 ± 3.1 yrs) ascended 5 different step heights, while knee kinematics and quadriceps EMG data were collected. Knee flexion angle at foot-step contact, VMO-VL onset timing, and VMO/VL activation ratios were analyzed between groups and step heights using 2-factor analyses of variance (ANOVAs) with repeated measures (α = .05). RESULTS: Individuals with PFPS demonstrated 4.7° (P = .038) more knee flexion at foot-step contact than control subjects. Despite greater knee flexion with increased step height (P‹.001), no differences in onset timing or activation magnitude ratio were present between groups or across step heights. However, individuals with PFPS displayed a significantly increased activation duration ratio compared to the control group (P = .043). CONCLUSION: Quadriceps onset timing and activation magnitude during stair ascent was similar between individuals with and without PFPS, regardless of step height. Thus, the results of this study are in agreement with evidence indicating no difference in VMO-VL timing and VMO/VL activation magnitude ratio between individuals with and without PFPS.

J Orthop Sports Phys Ther. 2007;37(5):239-244; published online 15 March 2007. doi:10.2519/jospt.2007.2421

KEY WORDS: activation ratio, anterior knee pain, EMG, onset delay, stair climbing

STUDY DESIGN: Repeated-measures experi­mental design. OBJECTIVE: To examine the acute effects of static stretching on peak torque, the joint angle at peak torque, mean power output, and electromyo­graphic and mechanomyographic amplitudes and mean power frequency of the vastus lateralis and rectus femoris muscles during maximal eccentric isokinetic muscle actions. BACKGROUND: A bout of static stretching may impair muscle strength during isometric and concentric muscle actions, but it is unclear how static stretching may affect eccentric force production. METHODS AND MEASURES: Fifteen men (mean 6 SD age, 23.4 6 2.4 years) performed maximal eccentric isokinetic muscle actions of the dominant and nondominant knee extensor muscles at 60°·s–1 and 180°·s–1 on an isokinetic dynamometer, while electromyographic and mech­anomyographic amplitudes (root-mean-square) and mean power frequency were calculated for the vastus lateralis and rectus femoris muscles. Peak torque (Nm), the joint angle at peak torque (°), and mean power output (W) values were recorded by the dynamometer. Subsequently, the dominant lower extremity knee extensors underwent static stretching exercises, then the assessments were repeated. RESULTS: There were no stretching-related changes in peak torque, the joint angle at peak torque, mean power output, electromyographic or mechanomyographic amplitude, or mean power frequency (P>.05). However, there were expected velocity-related, limb-related, and muscle-related differences (P≤.05) that were unrelated to the stretching intervention. CONCLUSION: These results suggest that static stretching does not affect maximal eccentric isokinetic torque or power production, nor does it change muscle activation.  

J Orthop Sports Phys Ther. 2007;37(3):130-139. doi:10.2519/jospt.2007.2389 

KEY WORDS: EMG, muscle activation, muscle stiffness, stretching-induced force deficit

Changes in strength following concentric-only weight training and detraining are poorly understood. The purpose of this investigation was to examine the effects of unilateral concentric leg extension weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit (individual limb strength > bilateral strength / 2). Sixteen males volunteered to be subjects for this investigation (concentric training group, N = 8; control group, N = 8). The training group performed 8 weeks of training with the nondominant limb 3 times per week (3-5 sets x 6 repetitions), followed by 8 weeks of detraining. These subjects were tested pretraining, posttraining, and following detraining for maximal isometric strength at 3 joint angles (15, 45, and 75°) in both limbs as well as for the 1-repetition maximum (1-RM) concentric strength of the trained limb, untrained limb, and bilaterally. The results of this investigation indicated that the effects of the concentric weight training were not joint angle specific as the isometric strength increases occurred at all 3 joint angles. This effect was found in both limbs, indicating that cross-training occurred. The results of the 1-RM analyses showed that initially there was a bilateral deficit (untrained limb > bilateral, trained limb at pretraining). While the concentric training resulted in increases in 1-RM strength in the trained limb, untrained limb, and bilaterally, differences between bilateral strength and the untrained limb were reversed posttraining and the trained limb values exceeded both the bilateral and untrained limb values. Finally, the effects of detraining were more pronounced for isometric strength vs. 1-RM strength as there was a significant decrease from posttraining in the isometric scores, but the detraining 1-RM values were not significantly decreased from posttraining for either limb or bilaterally.

J Orthop Sports Phys Ther. 1997;25(4):264-270.

Key Words: knee, muscle, dynamic strength, exercise training

Eccentric resistance training is an important component of many rehabilitation protocols. The adaptations following eccentric training are poorly understood in relation to concentric training. The purpose of this investigation was to examine the effects of unilateral eccentric leg extension weight training and detraining on joint angle specificity, cross training, and the bilateral deficit. Seventeen males volunteered to be subjects for this investigation and were divided into an eccentric training group (N = 9) and a control group (N = 8). The eccentric group performed 8 weeks of unilateral eccentric weight training with the nondominant limb 3 times per week (3-5 sets of 6 repetitions) followed by 8 weeks of detraining. These subjects were tested pretraining, posttraining, and following detraining for maximal isometric strength at 3 joint angles (15°, 45°, and 75°) in both limbs as well as for the 1-repetition maximum (1-RM) eccentric strength of the trained limb, untrained limb, and bilaterally. The results of this investigation indicated that the effects of the eccentric weight training were joint angle specific [significant increases at 45° and 75° (p < 0.05)]. This effect was found in both limbs, indicating a cross-training effect that was joint angle specific. The results from the 1-RM analyses indicated that the bilateral deficit exists for eccentric contractions (untrained limb > bilateral at pretraining) and that unilateral eccentric training increases this effect (trained and untrained limbs > bilateral posttraining); however, the unilateral training also resulted in increased bilateral strength. Both the 1-RM and isometric analyses showed that the training effects persisted over 8 weeks of detraining.

J Orthop Sports Phys Ther. 1995;22(5):207-215.

Key Words: muscle strength, eccentric training, knee

During isokinetic knee testing, some subjects flex the trunk and contralateral knee during knee extension and extend the trunk and contralateral knee during knee flexion. This investigation assessed the effect of these extraneous movements on peak and constant joint angle torque (15° below horizontal). Twenty-one subjects performed isokinetic knee extensions and flexions at 60°/sec, 180°/sec, and 300°/sec under stabilized and nonstabilized conditions. The nonstabilized testing was performed with intentional trunk and contralateral leg movements. The stabilized condition resulted in greater torque values than the nonstabilized condition for extension and flexion for both peak torque and constant joint angle torque. The angle at which flexion peak torque occurred was further from full extension at 60°/sec and 180°/sec under the nonstabilized condition, while no differences were found for extension. These results indicate that extraneous movements can decrease torque output, which may be due to changes in muscle length caused by the extraneous movements.

J Orthop Sports Phys Ther. 1996;23(5):302-308.

Key Words: knee, muscle strength, stabilization