Efficiency of pedal forces during ergometer cycling

The aim of this study was to record the forces applied to the pedal during ergometer cycling and to calculate the effectiveness of these force vectors. Six healthy subjects rode a weight-braked bicycle ergometer at different work loads, pedaling rates, saddle heights, and pedal foot positions. The left lower limb and crank motions were recorded by a cinefilm camera and pedal reaction forces by a Kistler force measuring transducer mounted on the left pedal. The force effectiveness was computed as a ratio between the force tangential to instantaneous direction of pedal movement and the resultant force. The mean force efficiency ratio significantly increased by an increase of the ergometer work load or use of the anterior foot position instead of the posterior. It was not significantly changed due to alterations of the pedaling rate or saddle height.     

Effects of initial graft tension on the tibiofemoral compressive forces and joint position after anterior cruciate ligament reconstruction

BACKGROUND: The initial tension applied to an anterior cruciate ligament graft at the time of fixation modulates knee motion and the tibiofemoral compressive loads. PURPOSE: To establish the relationships between initial graft tension, tibiofemoral compressive force, and the neutral tibiofemoral position in the cadaveric knee. STUDY DESIGN: Controlled laboratory study. METHODS: The tibiofemoral compressive forces and joint positions were determined in the anterior cruciate ligament-intact knee at 0 degrees , 20 degrees , and 90 degrees of knee flexion. The anterior cruciate ligament was excised and reconstructed with a patellar tendon graft using graft tensions of 1, 15, 30, 60, and 90 N applied at 0 degrees , 20 degrees , and 90 degrees of knee flexion. The compressive forces and neutral positions were compared between initial tension conditions and the anterior cruciate ligament-intact knee. RESULTS: Increasing initial graft tension increased the tibiofemoral compressive forces. The forces in the medial compartment were 1.8 times those in the lateral compartment. The compressive forces were dependent on the knee angle at which the tension was applied. The greatest compressive forces occurred when the graft was tensioned with the knee in extension. An increase in initial graft tension caused the tibia to rotate externally compared with the anterior cruciate ligament-intact knee (1.5 degrees and 7.7 degrees of external rotation when tensioned to 90 N at 0 degrees and 90 degrees of knee flexion, respectively). Increases in initial graft tension also caused a significant posterior translation of the tibia relative to the femur (0.9 and 5.3 mm of posterior translation when tensioned to 90 N at 0 degrees and 90 degrees of knee flexion, respectively). CONCLUSION: Different initial graft tension protocols produced predictable changes in the tibiofemoral compressive forces and joint positions. CLINICAL RELEVANCE: The tibiofemoral compressive force and neutral joint position were best replicated with a low graft tension (1-15 N) when using a patellar tendon graft.     

Effects of moving forward or backward on the saddle on knee joint forces during cycling

ObjectivesTo examine the effects of cycling at preferred, forward and backward saddle positions on patellofemoral compressive and tibiofemoral compressive and shear forces.DesignCross-sectional.SettingAn incremental cycling test to exhaustion determined cyclists' maximal aerobic workload and second ventilatory threshold. In a second session, 1-min cycling trial at maximal aerobic workload then three 2-min trials at second ventilatory threshold workload at preferred, forward and backward saddle positions. Right pedal force via instrumented pedals, lower limb joint kinematics via video and inverse dynamics were used to calculate knee joint forces.ParticipantsTwenty-one competitive cyclists (28 ± 7 years).Main outcome measuresPatellofemoral compressive, tibiofemoral compressive and shear forces, and knee flexion angle.ResultsChanges to forward/backward saddle positions did not substantially affect compressive forces for patellofemoral (1–4%) or tibiofemoral (1–3%) joints. Tibiofemoral shear force increased in backward compared with preferred (19%) or forward (26%) saddle positions. Knee flexion angle at 3 o'clock (22%) and 6 o'clock crank positions (36%) increased at the forward compared to the backward saddle position.ConclusionsSmall increases in knee flexion angle (5–6°) explained trivial differences in patellofemoral and tibiofemoral compressive forces. Tibiofemoral shear force may be more sensitive to changes in knee joint angle compared to other knee force components.     

Tibiofemoral joint forces during isokinetic knee extension

Using a Cybex II, eight healthy male subjects performed isokinetic knee extensions at two different speeds (30 and 180 deg/sec) and two different positions of the resistance pad (proximal and distal). A sagittal plane, biomechanical model was used for calculating the magnitude of the tibiofemoral joint compressive and shear forces. The magnitude of isokinetic knee extending moments was found to be significantly lower with the resistance pad placed proximally on the leg instead of distally. The tibiofemoral compressive force was of the same magnitude as the patellar tendon force, with a maximum of 6300 N or close to 9 times body weight (BW). The tibiofemoral shear force changed direction from being negative (tibia tends to move posteriorly in relation to femur) to a positive magnitude of about 700 N or close to 1 BW, indicating that high forces arise in the ACL when the knee is extended more than 60 degrees. The anteriorly directed shear force was lowered considerably by locating the resistance pad to a proximal position on the leg. This model may be used when it is desirable to control stress on the ACL, e.g., in the rehabilitative period after ACL repairs or reconstructions.     

Downhill walking: A stressful task for the anterior cruciate ligament?

Accelerated rehabilitation after anterior cruciate ligament (ACL) reconstruction has become increasingly popular. Methods employed include immediate extension of the knee and immediate full weight bearing despite the risks presented by a graft pull-out fixation strength of 200–500 N. The purpose of this study was to calculate the tibiofemoral shear forces and the dynamic stabilising factors at the knee joint for the reasonably demanding task of downhill walking, in order to determine whether or not this task presented a postoperative risk to the patient. Kinematic and kinetic data were collected on six male and six female healthy subjects during downhill walking on a ramp with a 19% gradient. Planer net joint moments and mechanical power at the knee joint were calculated for the sagittal view using a force platform and videographic records together with standard inverse dynamics procedures. A two-dimensional knee joint model was then utilised to calculate the tibiofemoral shear and compressive forces, based on the predictions of joint reaction force and net moment at the knee. Linear envelopes of the electromyographic (EMG) activity recorded from the rectus femoris, gastrocnemius and biceps femoris muscles were also obtained. The maximum tibiofemoral shear force occurred at 20% of stance phase and was, on average, 1.2 times body weight (BW) for male subjects and 1.7 times BW for female subjects. The tibiofemoral compressive force was 7 times BW for males and 8.5 times BW for females during downhill walking. The hamstring muscle showed almost continuous activity throughout the whole of the stance phase. The gastrocnemius muscle had its main activity at heelstrike, with a second brust during the late stance phase. Knee joint shear force predictions of approximately 1000 N for a 70-kg subject greatly exceed the strength of a typical ACL graft fixation and muscular stabilisation of the knee is therefore vital to joint integrity. The hamstring muscle shows almost continuous activity during the stance phase and thereby affords some stability, but the gastrocnemius is also seen to be an important stabiliser of the knee joint in the presence of increased shear forces during early stance. Associated stability to the knee joint is indicated by compressive loadings of 7–8 times BW across the tibiofemoral joint. Whereas under normal circumstances there is sufficient dynamic joint stabilisation during downhill walking, the muscular impairment often arising postoperatively from disturbed proprioception could endanger an ACL graft. Therefore downhill walking should be avoided during the postoperative phase in order to protect the reconstruction.This research was conducted in the Department of Human Movement at The University of Western Australia. Perth during the first author's tenure as a Visiting Research Fellow supported by a scholarship of the Swiss Orthopaedic Association (SGO)     

Dynamic joint forces during knee isokinetic exercise

This study analyzed forces in the tibiofemoral and patellofemoral joints during isokinetic exercise using an analytical biomechanical model. The results show that isokinetic exercise can produce large loads on these joints, especially during extension exercises. The tibiofemoral compressive force (4.0 body weight) is approximately equal to that obtained during walking but it occurs at 55 degrees of knee flexion. Anterior shear forces (resisting force to anterior drawer) exist during extension exercise at less than 40 degrees of knee flexion, with a maximum of 0.3 body weight. Posterior shear forces (resisting force to posterior drawer) exist during extension exercise at knee joint angles greater than 40 degrees and during the flexion portion of isokinetic exercise. The maximum posterior shear force is 1.7 body weight. The patellofemoral joint can encounter loads as high as 5.1 body weight which are 10 times higher than during straight leg raises. These results suggest that isokinetic exercise should be used cautiously in patients with knee lesions.     

Compressive tibiofemoral force during crouch gait

Crouch gait, a common walking pattern in individuals with cerebral palsy, is characterized by excessive flexion of the hip and knee. Many subjects with crouch gait experience knee pain, perhaps because of elevated muscle forces and joint loading. The goal of this study was to examine how muscle forces and compressive tibiofemoral force change with the increasing knee flexion associated with crouch gait. Muscle forces and tibiofemoral force were estimated for three unimpaired children and nine children with cerebral palsy who walked with varying degrees of knee flexion. We scaled a generic musculoskeletal model to each subject and used the model to estimate muscle forces and compressive tibiofemoral forces during walking. Mild crouch gait (minimum knee flexion 20-35°) produced a peak compressive tibiofemoral force similar to unimpaired walking; however, severe crouch gait (minimum knee flexion>50°) increased the peak force to greater than 6 times body-weight, more than double the load experienced during unimpaired gait. This increase in compressive tibiofemoral force was primarily due to increases in quadriceps force during crouch gait, which increased quadratically with average stance phase knee flexion (i.e., crouch severity). Increased quadriceps force contributes to larger tibiofemoral and patellofemoral loading which may contribute to knee pain in individuals with crouch gait.     

Muscle, ligament, and joint-contact forces at the knee during walking

PURPOSE: In vivo measurement of the forces and strains in human tissues is currently impracticable. Computer modeling and simulation allows estimates of these quantities to be obtained noninvasively. This paper reviews our recent work on muscle, ligament, and joint loading at the knee during gait. METHODS: Muscle and ground-reaction forces obtained from a sophisticated computer simulation of walking were input into a detailed model of the lower limb to obtain ligament and joint-contact loading at the knee for one full cycle of gait. RESULTS: Peak anterior cruciate ligament (ACL) force occurred in early stance and was mainly determined by the anterior pull of the patellar tendon on the tibia. The medial collateral ligament was the primary restraint to anterior tibial translation (ATT) in the ACL-deficient knee. ATT in the ACL-deficient knee can be reduced to the level calculated for the intact knee by increasing hamstrings muscle force. Reducing quadriceps force was insufficient to restore ATT to the level calculated for the intact knee. For both normal and ACL-deficient walking, the resultant force acting between the femur and tibia remained mainly on the medial side of the knee. The knee adductor moment was resisted by a combination of muscle and ligament forces. CONCLUSION: Knee-ligament loading during the stance phase of gait is explained by the pattern of anterior shear force applied to the leg. The distribution of force at the tibiofemoral joint is determined by the variation in the external adductor moment applied at the knee. The forces acting at the tibiofemoral and patellofemoral joints are similar during normal and ACL-deficient gait. Hamstrings facilitation is more effective than quadriceps avoidance in reducing ATT during ACL-deficient gait.     

Foot force direction control during leg pushes against fixed and moving pedals in persons post-stroke

The component of foot force generated by muscle action (F(m)) during pedaling in healthy humans has a nearly constant direction with increasing force magnitude. The present study investigated the effect of stroke on the control of foot force. Ten individuals with hemiparesis secondary to a cerebral vascular accident performed pushing efforts against translationally fixed and moving pedals on a custom stationary cycle ergometer. We found that while F(m) direction remained constant with increasing effort in both the fixed- and moving-crank conditions for both limbs, the orientation of that force component differed between limbs. The non-paretic limb produced the same F(m) orientation as seen previously in healthy humans. However, relative to the non-paretic limb, the paretic limb force line-of-action was shifted away from the hip and closer to the knee in the sagittal-plane for both pedal motion conditions. In the frontal plane, the paretic limb force line-of-action was shifted laterally, closer to parallel to the midline, for both pedal motion conditions. These shifts were consistent with previously reported lower limb muscle weakness and alterations in muscle activation observed during pedaling tasks following stroke. The finding of similar orientations for static and dynamic pushing efforts suggests that limb posture could be a trigger for relative muscle activation levels. The preservation of a constant direction in F(m) with increasing force magnitude post-stroke, despite an orientation shift, suggests that control of lower limb force may be organized by magnitude and direction and that these two aspects are differentially affected by stroke.     

Effect of Alpine ski boot cuff release on knee joint force during the backward fall

The modern rigid alpine ski boot has been associated with an increase in severe knee joint injuries. A new design that allows the rear portion of the upper cuff of the boot (rear spoiler) to open when a posterior directed force is applied to it (similar to when a skier falls back on the ski) is investigated. Motion analysis was combined with kinetic measures to estimate the shear and compressive forces at the knee joint using a link-segment model while subjects fell backward to provoke ski boot cuff release. The rear spoiler opening was found to reduce anterior cruciate ligament directed shear force while increasing compressive force at the joint. We conclude that both compressive force and reduced anterior cruciate directed shear force have been associated with protective mechanisms at the knee joint. This occurred over a very brief period of time, however, and the influence this may have on knee injury prevention is discussed.     

Knee biomechanics of the dynamic squat exercise

PURPOSE: Because a strong and stable knee is paramount to an athlete's or patient's success, an understanding of knee biomechanics while performing the squat is helpful to therapists, trainers, sports medicine physicians, researchers, coaches, and athletes who are interested in closed kinetic chain exercises, knee rehabilitation, and training for sport. The purpose of this review was to examine knee biomechanics during the dynamic squat exercise. METHODS: Tibiofemoral shear and compressive forces, patellofemoral compressive force, knee muscle activity, and knee stability were reviewed and discussed relative to athletic performance, injury potential, and rehabilitation. RESULTS: Low to moderate posterior shear forces, restrained primarily by the posterior cruciate ligament (PCL), were generated throughout the squat for all knee flexion angles. Low anterior shear forces, restrained primarily by the anterior cruciate ligament (ACL), were generated between 0 and 60 degrees knee flexion. Patellofemoral compressive forces and tibiofemoral compressive and shear forces progressively increased as the knees flexed and decreased as the knees extended, reaching peak values near maximum knee flexion. Hence, training the squat in the functional range between 0 and 50 degrees knee flexion may be appropriate for many knee rehabilitation patients, because knee forces were minimum in the functional range. Quadriceps, hamstrings, and gastrocnemius activity generally increased as knee flexion increased, which supports athletes with healthy knees performing the parallel squat (thighs parallel to ground at maximum knee flexion) between 0 and 100 degrees knee flexion. Furthermore, it was demonstrated that the parallel squat was not injurious to the healthy knee. CONCLUSIONS: The squat was shown to be an effective exercise to employ during cruciate ligament or patellofemoral rehabilitation. For athletes with healthy knees, performing the parallel squat is recommended over the deep squat, because injury potential to the menisci and cruciate and collateral ligaments may increase with the deep squat. The squat does not compromise knee stability, and can enhance stability if performed correctly. Finally, the squat can be effective in developing hip, knee, and ankle musculature, because moderate to high quadriceps, hamstrings, and gastrocnemius activity were produced during the squat.     

The effect of internal and external foot rotation on the adduction moment and lateral–medial shear force at the knee during gait

It has been hypothesised that those with medial compartment knee osteoarthritis tend to externally rotate their foot during gait in order to unload the diseased compartment. This has been found to decrease the adduction moment at the knee during late stance, although the effects of foot rotation on shear forces at the knee have not yet been determined. Also, the effects of internal foot rotation on the knee during gait are not clear. This study performed a gait analysis on 11 healthy participants (M: 6; mean age 22.9 ± 1.8 years) in three conditions: (1) natural foot rotation position; (2) internal foot rotation and (3) external foot rotation. Three-dimensional gait analysis calculated the knee adduction moment and lateral–medial shear force for all three foot rotation conditions. Internal rotation of the foot increased the knee adduction moment and lateral–medial shear force magnitude during late stance, while external rotation of the foot decreased the magnitude of both these measures. This implies that walking with an externally and internally rotated foot may unload the diseased compartment for those with medial and lateral compartment knee OA, respectively. Also, the relationship of foot rotation angle to the adduction moment and lateral–medial shear force was strengthened when data were corrected for the subject's normal walking condition. Knee OA subject data revealed that they were able to reduce the knee adduction moment more than normal subjects during late stance, indicating that other factors besides the rotation of the foot need to be investigated.     

Model prediction of anterior cruciate ligament force during drop-landings

PURPOSE: The aim of this study was to calculate and explain the pattern of force transmitted to the anterior cruciate ligament during soft-style drop-landings. We hypothesized that peak ACL loading is due to the anterior pull of the quadriceps on the tibia, as these muscles develop large eccentric forces upon impact. METHODS: A three-dimensional model of the body was used to simulate drop-landing. The simulation was performed by entering into the model muscle excitation patterns based on experimental EMG. The input excitation patterns were modified to create a performance response of the model that matched experimental data. Joint angles, ground reaction forces, and muscle forces obtained from the landing simulation were then applied to a model of the lower limb that incorporated a three-dimensional model of the knee. RESULTS: The model ACL was loaded only in the first 25% of the landing phase. Peak ACL force (approximately 0.4 BW) resulted from a complex interaction between the patellar tendon force, the compressive force acting at the tibiofemoral joint, and the force applied by the ground to the lower leg. The patellar tendon force and tibiofemoral contact force both applied significant anterior shear forces to the shank throughout the landing phase. These effects were modulated by another significant posterior shear force applied by the ground reaction, which served to limit the maximum force transmitted to the ACL. CONCLUSION: The pattern of ACL force in drop-landing cannot be explained by the anterior pull of the quadriceps force alone.     

Frontal plane knee angle affects dynamic postural control strategy during unilateral stance

PURPOSE: Center of plantar pressure (COPP) location moves toward the forefoot as ankle plantar flexor muscles attempt to maintain postural control during single leg stance. This study evaluated relationships between frontal plane tibiofemoral joint angulation during relaxed bilateral stance and mean COPP locations during vision-denied single leg stance at 20 degrees knee flexion. METHODS: Fifty-six nonimpaired athletes (29 female, 27 male) were evaluated for frontal plane tibiofemoral joint angulation and standing foot angle by using two-dimensional videography (30 Hz). Mean anterior-posterior and mediolateral COPP locations were assessed during single leg stance on a mat (25 Hz, 15 s). One-way ANOVA and Tukey HSD tests evaluated group differences (P < or = 0.05) based on frontal plane tibiofemoral joint angulation. RESULTS: Group 1 (genu varus or genu valgus < 5 degrees ) displayed a mean anterior-posterior COPP location of 54.2 +/- 6% from the (0,0) coordinate starting point at the anterolateral foot (10.3 +/- 2 cm from the posterior sensor edge). Group 2 (genu varus angulation > or = 5 degrees ) and group 3 subjects (genu valgus angulation > or = 5 degrees ) displayed mean anterior-posterior COPP locations of 60.6 +/- 8% and 60.7 +/- 7% (8.8 +/- 2 cm and 8.7 +/- 2 cm from the posterior sensor edges), respectively. Group 2 (12.5 +/- 3 N x kg(-1)) and group 3 (12.4 +/- 3.1 N x kg(-1)) subjects also displayed greater mean plantar force magnitude/body weight than group 1 (10.3 +/- 2 N x kg(-1)) subjects. Mean ankle plantar flexor moment magnitudes did not differ between groups. CONCLUSIONS: Rearfoot directed mean anterior-posterior COPP locations and greater plantar force magnitudes/body weight suggests that subjects with genu varus or genu valgus relied more on the subtalar and midtarsal joint control function of the ankle plantar flexor muscle group for lower extremity dynamic postural control.     

Some effects of knee angle and foot placement in bicycle ergometer

The aim of this study was to examine the effect on heart rate, blood pressure and RPE on a bicycle ergometer performed with three different ways, i.e. with the anterior part of the foot, the posterior part of the foot and at saddle height with a knee angle of 120 degrees-125 degrees of submaximal and maximal work load. Untrained female (age X = 22 +/- 2.10 years, weight X = 56 +/- 5.4 kg, height X = 162 +/- 5.25 cm) volunteered as subjects. Heart rate and RPE at work load of 100 Watts were significantly lower in cycling with anterior part of the foot than with posterior part of the foot, while RPE in cycling with the posterior part of the foot was significantly lower in comparison to cycling with a knee angle of 120 degrees-125 degrees. Thirty three subjects were able to complete cycling on the load of 125 W with the anterior part of the foot; 28 with the posterior part of the foot and 22 with a knee angle of 120 degrees-125 degrees. It was concluded that cycling, (a) with the anterior part of the foot and the knee almost fully extended, is perceived easier and is more effective; (b) with the posterior part of the foot is tiring and ineffective and (c) with a low height of the saddle affects muscular work negatively.     

Effect of knee flexion on the in situ force distribution in the human anterior cruciate ligament

This study was conducted to evaluate the effect of applied load on the magnitude, direction, and point of tibial intersection of the in situ forces of the anteromedial (AM) and posterolateral (PL) bands of the human anterior cruciate ligament (ACL) at 30° and 90° of knee flexion. An Instron was used to apply a 100 N anterior shear force to 11 human cadaver knees, 6 at 30° of knee flexion and 5 at 90° of knee flexion. A Universal Force Sensor (UFS) recorded the resultant 6 degree-of freedom (DOF) forces/moments. Each specimen then underwent serial removal of the AM and PL bands. With the knee limited to 1 DOF (anteroposterior), tests were performed before and after each structure was removed. Because the path was identical in each test, the principle of superposition was applied. Thus, the difference between the resultant forces could be attributed to the force carried by the structure just removed. The magnitudes of force in the ACL at 30° and 90° of knee flexion were 114.1±7.4 N and 90.8±8.3 N, respectively (P<0.05). At 30°, the AM and PL bundles carried 95% and 4% of the total ACL force, respectively. At 90°, the AM and PL bands carried 85% and 13%, respectively (P<0.05). The direction of the in situ force in the whole ACL as well as its two bands correlated with the anatomic orientation of the ligament. The resultant total ACL force intersected the tibial plateau at the posterolateral aspect of the AM band's insertion at 30° of knee flexion, while at 90°, the force intersection moved posteriorly to the AM/PL border. This research provides new insight into the fundamental force relationships of the ACL and its bundles. In response to an anterior tibial shear force, the AM band of the ACL was the predominant load carrier at both 30° and 90° of knee flexion. However, contrary to carlier reports, the in situ force carried in the PL band increased as knee flexion increased. Further, the tibial intersection of the resultant ACL force moved laterally with knee flexion. These findings confirm the dynamic structure of the ACL that in itself has no isometricity and may also indicate that there is no ideal location in which to position a replacement graft. The use of this methodology with more physiologically unconstrained motion should lead to more definitive clinical conclusions.     

Tibiofemoral joint contact forces and knee kinematics during squatting

Axial tibiofemoral joint contact forces were non-invasively determined for two high range of motion (high flexion) squatting activities. An electromagnetic motion tracking system and a non-conductive force platform were used to collect kinematic and kinetic data. An innovative scaling method was used to model subject-specific muscle group moment arms. One subject attained a peak axial tibiofemoral joint contact force of 49.7 N/kg during squatting at 149.9 degrees knee flexion. Average joint angles and average axial joint contact forces were calculated for each of the activities in order to facilitate a comparison with stair climbing data. Compared to stair climbing, the maximum average joint contact forces during the squatting activities occurred at significantly higher flexion angles (p<0.05.) The relative simplicity of the method makes it useful for application to large subject groups from diverse regions. The results of this study can be applied to the diagnosis and treatment of pathologies, and to the development of high range of motion (ROM) knee replacements.     

Effect of fatigue on knee kinetics and kinematics in stop-jump tasks

BACKGROUND: Altered motor control strategies in landing and jumping maneuvers are a potential mechanism of noncontact anterior cruciate ligament injury. There are biomechanical differences between male and female athletes in the landing phase of stop-jump tasks. Fatigue is a risk factor in musculoskeletal injuries. HYPOTHESIS: Lower extremity muscle fatigue alters the knee kinetics and kinematics during the landing phase of 3 stop-jump tasks and increases an athlete's risk of anterior cruciate ligament injury. STUDY DESIGN: Controlled laboratory study. METHODS: Three-dimensional videography and force plate data were collected for 20 recreational athletes (10 male and 10 female athletes) performing 3 stop-jump tasks before and after completing a fatigue exercise. Knee joint angles and resultant forces and moments were calculated. RESULTS: Both male and female subjects had significantly increased peak proximal tibial anterior shear forces (P = .01), increased valgus moments (P = .03), and decreased knee flexion angles (P = .03) during landings of all 3 stop-jump tasks when fatigued. Fatigue did not significantly affect the peak knee extension moment for male or female athletes. CONCLUSION: Fatigued recreational athletes demonstrate altered motor control strategies, which may increase anterior tibial shear force, strain on the anterior cruciate ligament, and risk of injury for both female and male subjects. CLINIC RELEVANCE: Fatigued athletes may have an increased risk of noncontact anterior cruciate ligament injury.     

Knee and hip kinetics during normal stair climbing

Understanding joint kinetics during activities of daily living furthers our understanding of the factors involved in joint pathology and the effects of treatment. In this study, we examined hip and knee joint kinetics during stair climbing in 35 young healthy subjects using a subject-specific knee model to estimate bone-on-bone tibiofemoral and patello-femoral joint contact forces. The net knee forces were below one body weight while the peak posterior-anterior contact force was close to one body weight. The peak distal-proximal contact force was on average 3 times body weight and could be as high as 6 times body weight. These contact forces occurred at a high degree of knee flexion where there is a smaller joint contact area resulting in high contact stresses. The peak knee adduction moment was 0.42 (0.15) Nm/kg while the flexion moment was 1.16 (0.24) Nm/kg. Similar peak moment values, but different curve profiles, were found for the hip. The hip and knee posterior-anterior shear forces and the knee flexion moment were higher during stair climbing than during level walking. The most striking difference between stair ascent and level walking was that the peak patello-femoral contact force was 8 times higher during stair ascent. These data can be used as baseline measures in pathology studies, as input to theoretical joint models, and as input to mechanical joint simulators.     

Biomechanics during exercise with a novel stairclimber

The current study aimed to investigate the stair-climbing biomechanics related to the lower extremities when subjects used the novel designed stair-climber, which could provide opportunity for both sagittal and frontal movements. 12 volunteers were required to step while either keeping the trunk static (STATIC) or allowing the trunk to shift with weight bearing (SHIFT). A motion analysis system and the 6-axis force and torque sensor embedded in the pedal were used to collect data. Foot contact forces and joint moments were calculated to represent loading characteristics. The joint angle and corresponding moments at the terminal point of the stance phase were computed to serve as the indicator of safety. Significant differences were found in peak foot contact forces, knee extensor moment, and hip abductor moment. At the end of the stance phase, various directions of moment between conditions were found in the knee and the ankle. The knee valgus angle, hip abductor moment, and knee extensor moment were significantly greater in SHIFT than in STATIC. The various stepping strategies caused differences in joint loading characteristics; therefore, these findings need to be given greater consideration in the design of training protocols.