Yoshinori Kimura

MOTION ANALYSIS OF A SINGLE-LIMB SQUAT WITH ISOKINETIC RESISTANCE

Background Resistive lateral leg reach exercise (RLLR), a single-limb squat with resistance, increases load on the gluteal muscles and is effective for preventing knee valgus moment, a major factor in anterior cruciate ligament (ACL) injury. To enhance the load during RLLR, we devised a novel isokinetic exercise machine. Objective To investigate the biomechanical and electromyographic (EMG) characteristics of the support leg during RLLR with isokinetic resistance (RLLR-I). Design Quasi-experimental. Setting Controlled laboratory setting. Participants 8 asymptomatic recreational-level female college athletes. Intervention Participants performed RLLR-I and lateral leg reach without resistance (LLR). The resistance device was set to 25 cm/s during RLLR-I. A three-dimensional motion capture system and force plate were used for motion analysis. Surface electrodes recorded the EMG at each muscle site: gluteus maximus (GMa), gluteus medius (GMe), rectus femoris, vastus medialis (VM), biceps femoris, adductor longus, soleus, and gastrocnemius. Main outcome measurements The external knee valgus/varus moment and the internal joint moment of the support leg were calculated using software. EMG root mean squared amplitude was normalized as a percentage of maximum voluntary contraction (%MVC). Results RLLR-I was characterized by a significantly larger internal hip abduction moment (2.2±1.0 Nm/kg) and significantly larger VM (152±54 %MVC), GMa (92±47 %MVC), and GMe (97±33 %MVC) activity compared with LLR (hip abduction moment: 1.5±0.7 Nm/kg; VM: 102±40 %MVC; GMa: 35±25 %MVC; and GMe: 38±13 %MVC). No significant external knee valgus moment occurred during RLLR-I. Conclusion RLLR-I serves to increase the load on the VM and gluteal muscles and is effective for preventing external knee valgus moment. These findings suggest that this novel isokinetic exercise will be useful for preventing ACL injury and in rehabilitation after ACL reconstruction.

BIOMECHANICAL ANALYSIS OF SINGLE-LEG SQUAT WITH ISOKINETIC AND CONSTANT RESISTIVE FORCE USING CONTROLLABLE EXERCISE EQUIPMENT

Background We have reported that a resistive single-leg squat (RSLS) exercise using exercise equipment that generates various resistance forces was effective for increasing the load on the gluteus medius and preventing knee valgus moment. However, the biomechanical characteristics of RSLS with each resistance forces have not been compared. Objective To compare difference of the biomechanical characteristics of RSLS between isokinetic resistance force (IF) and constant resistance force (CF). Design Quasi-experimental. Setting Controlled laboratory setting. Participants Six asymptomatic female college students. Interventions Participants performed RSLS with IF and CF. A motion capture system and force plate were used for motion analysis. Surface electrodes recorded the EMG activity of the muscles of the support leg. Main Outcome Measurements Joint moment of the support leg were calculated from 20° to 60° of knee flexion at 10° intervals. EMG data were normalized as a percentage of maximum voluntary contraction. Results In both the tasks, external knee valgus moment was prevented. Peak internal hip abduction moment was larger in IF (2.3±0.4 Nm/kg) than in CF (1.91±0.3 Nm/kg). Internal hip abduction moment was significantly larger in CF (1.4±0.2 Nm/kg) than in IF (1.1±0.3 Nm/kg) at 20° knee flexion, but larger in IF than in CF at 50° and 60° knee flexion. No significant difference in internal hip abduction moment was found at 30° and 40° knee flexion. EMG activities were significantly larger in IF (rectus femoris, 56±16%; vastus medialis, 85±38%; gluteus medius, 85±17%) than in CF (rectus femoris, 34±10%; vastus medialis, 48±23%; gluteus medius, 59±12%). Conclusion: IF was more useful for augmenting the activity of major muscles in the support leg and internal hip abduction moment at large knee flexion angles, whereas CF was more useful for augmenting internal hip abduction moment at small knee flexion angles, where ACL injury frequently occurs.

THE EFFECTS OF FUNCTIONAL GARMENT ON THE JUMP LANDING TASK

Background The effectiveness of wearing a brace to prevent sports injuries of the knee remains controversial. We examined the impact of functional newly developed garments. Objective To investigate the biomechanics of the knee joint when wearing the functional garment with lines in the fabric of different elasticities. Design Quasi-experimental. Setting Controlled laboratory setting. Participants 22 healthy male and female college students who participated in recreational sports. Interventions A single-leg drop jump onto the force plate was performed from a height of 30 cm. Infrared-reflective markers were attached to a total of 39 points for each subject. Body movements were tracked using a high-speed (200 Hz) three-dimensional motion analyzer and a force plate (ground reaction force of 1000 Hz). Long garments were used: two types of garments with fabric lines of hard and soft elasticity and the same garment with no processing (NT) as a control. Main outcome measurements External knee and knee valgus-varus moments as well as joint angle of the support leg were calculated using computer software. Results At 40 ms after ground contact, a significant decrease in the knee valgus angle was observed when wearing the Hard garment (5.33±3.32°) compared to the NT garment (1.33±4.91°; P<.05). A significantly low knee valgus-varus moment was observed when wearing the Hard garment (–6.08±7.07 Nm/kg) compared with the NT garment (0.93±8.60 Nm/kg) (P<.05). Conclusion The developed functional garment is considered to have reduced the knee abduction moment by controlling the knee valgus moment in a single-leg drop jump.The garment has the potential to avoid malalignment of the lower extremity and prevent sports injury of the knee joint.

EVALUATION OF A NEW QUADRICEPS STRENGTHENING EXERCISE FOR THE PREVENTION OF SECONDARY CARTILAGE INJURY IN PATIENTS WITH PCL INSUFFICIENCY: COMPARISON OF TIBIAL MOVEMENT IN PRONE AND SITTING POSITIONS DURING THE EXERCISE

Background Quadriceps strengthening exercise is recommended for patients with PCL insufficiency (PCLI), but posterior sag may occur under the influence of gravity in general leg extension in the sitting position (LES). We hypothesized that leg extension in the prone position (LEP) would be a safe strengthening exercise because the tibia is repositioned in patients with PCLI. Objective To compare tibial displacement (step off: SO) between LEP and LES, in order to verify the safety of LEP. Design Quasi-experimental study. Setting Controlled laboratory research. Patients 6 patients with PCL insufficiency (SO 2.9±1.6 mm). Interventions: LEP and LES were performed for isometricstrengthening with a flexion angle of the knee of 60 degrees and consistent force of knee extension. SO was measured on lateral X-P images of the knee. Differences in tibial movement between LEP and LES were evaluated using a paired t-test (P<0.05). Main outcome measurement SO measured by digitized XP. Results At the start position of LES, the tibia of all subjects was displaced posteriorly, and the tibia moved anteriorly 7.1±3.1 mm upon contraction of the quadriceps. In contrast, at the start position of LEP, the tibia was not displaced posteriorly in any subjects (SO=− 2.9±2.7 mm). Furthermore, there was significantly less anterior movement of the tibia during LEP (2.8±3.5 mm) than during LES (P<.05). Conclusions Since LES produced excessive anterior movement of the tibia upon contraction of the quadriceps, secondary cartilage injury may occur because of increased compression and shear force. In contrast, the repositioning of the tibia in LEP by gravity indicates it could be a safe quadriceps strengthening exercise for PCL insufficiency.

Safe and effective quadriceps femoris muscle exercise of resisted front bridge with a leg support in patients with anterior cruciate ligament insufficiency

Background Muscle strengthen exercise of quadriceps femoris is important but risky to the anterior cruciate ligament (ACL) graft, because quadriceps muscle exercise near the knee extension may causes anterior tibial translation. We developed a new exercise method, ‘resisted front bridge exercise with a leg support at proximal tibia’ (RFBP) in a prone position to avoid a risk. Our hypothesis is that RFBP is safe for the ACL graft and effective for muscle strengthen exercise. Objective To test our hypothesis, we investigated the anterior tibial translation and muscle contraction of quadriceps femoris during RFBP and compared with a front bridge exercise with a leg support at distal tibia (FBD). Design Quasi-experimental study. Setting Controlled laboratory research. Patients Three patients with ACL insufficiency participated in this study approved by the institutional ethical committee. Interventions Patients lied in a prone position with a leg support at proximal tibia. Leg extension exercise was ordered with a 20% of body-weight load on the back thigh to perform ‘RFBP’. Main outcome measurements Anterior tibial translation at 15° knee flexion was measured by fluoroscopy according to Franklins method. Electromyography (EMG) of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) were recorded and normalised against the values of maximum voluntary contraction (%MVC) of the involved leg. Results Anterior tibial translation of the involved knee in RFBP was not statistically significantly different from that of the uninvolved knee, and was smaller than that of the uninvolved knee in FBD in all patients by 4.4 mm in average. The%MVC of VM, VL, and RF muscle activities in the involved knee were 101.8%, 68.2%, and 75.6% during RFBP, respectively. Conclusion The resisted front bridge exercise with a leg support at proximal tibia is safe and effective for the quadriceps femoris at 15° knee flexion following ACL reconstruction surgery.