Perceived submaximal force production in young adult males and females

Clinical treatment in physical rehabilitation routinely uses perceived relative forces. PURPOSE: This study used psychophysical methods to quantify subjects' errors during submaximal muscular force production. METHODS: A sample of young adult (aged 23 +/- 3 yr) females (N = 60, 62 +/- 14 kg) and males (N = 50, 72 +/- 13 kg) performed a chest press on a hydraulic dynamometer with which they were unfamiliar. In four consecutive presses with a 2-min rest interval between each press, the subjects were asked to produce a force in the order of 25%, 50%, 75% of their maximal force, and a final maximal press. Pilot data (N = 10) indicated good reliability (r(xx) > 0.80) for the protocol. RESULTS: The rs between perceived force production and the desired production were 0.76 (P < 0.001) for males and 0.75 (P < 0.001) for females. The exponent for the power function between the perceived and desired forces was 1.12 for males and 1.03 for females. The total error ranged from 2.82 kg x m (males) to 1.22 kg x m (females). The rs and the logarithmic matching of perceived and desired force indicated a linear relationship that is consistent with Borg's range model, which has proposed that perceptual intensities of force for different people are approximately set equal at a subjective maximum. CONCLUSION: Many young healthy subjects can produce relative muscular forces with good accuracy. However, some subjects will provide very inaccurate forces that might affect outcomes in rehabilitation or physical training.     

Biomechanical analysis of tibial torque and knee flexion angle: implications for understanding knee injury

Knee injuries are common in sports activities. Understanding the mechanisms of injury allows for better treatment of these injuries and for the development of effective prevention programmes. Tibial torque and knee flexion angle have been associated with several mechanisms of injury in the knee. This article focuses on the injury to the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL) and the meniscus of the knee as they relate to knee flexion angle and tibial torque. Hyperflexion and hyperextension with the application of tibial torque have both been implicated in the mechanism of ACL injury. A combination of anterior tibial force and internal tibial torque near full extension puts the ACL at high risk for injury. Hyperflexion also increases ACL force; however, in this position, internal and external tibial torque only minimally increase ACL force. Several successful prevention programmes have been based on these biomechanical factors. Injury to the PCL typically occurs in a flexed or hyperflexed knee position. The effects of application of a tibial torque, both internally and externally, remains controversial. Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while others have shown that PCL-deficient knees have greater external tibial rotation. The meniscus must endure greater compressive loads at higher flexion angles of the knee and, as a result, are more prone to injury in these positions. In addition, ACL deficiency puts the meniscus at greater risk for injury. Reducing the forces on the ACL, PCL and meniscus during athletic activity through training, the use of appropriate equipment and safe surfaces will help to reduce injury to these structures.     

Concentric and eccentric shoulder and elbow muscle strength in female volleyball players and non-active females

Alfredson H, Pietilä T, Lorentzon R. Concentric and eccentric shoulder and elbow muscle strength in female volleyball players and non-active females. Maximal isokinetic concentric (60°/s and 180°/s) and eccentric (60°/s) muscle strength of the external and internal rotator muscles of the shoulder and the flexor and extensor muscles of the elbow was measured in a position resembling spiking and serving in volleyball, on 11 non-injured female volleyball players (first division) and 11 non-active females. In the dominant arm, the volleyball players had significantly higher concentric peak torque of the internal and external rotators and elbow extensors at both velocities, and significantly higher eccentric peak torque of the shoulder internal and external rotators and elbow flexors and extensors, than the controls. In the volleyball group, the concentric internal rotation peak torque at 60°/s was significantly higher in the dominant than in the non-dominant arm. The external/internal strength ratio was significantly lower at 60°/s, but not at 180°/s, in the dominant arm. Conclusion: The female volleyball players had a higher concentric and eccentric strength in the rotator muscles of the shoulder and in the extensor muscles of the elbow compared to untrained controls in this special test position. There were signs of rotator muscle imbalance at the low test speed, but no signs of weakness of the external rotators, in the dominant arm of the volleyball players.     

Changes in the orientation of knee functional flexion axis during passive flexion and extension movements in navigated total knee arthroplasty

Purpose

Recently, the functional flexion axis has been considered to provide a proper rotational alignment of the femoral component in total knee arthroplasty. Several factors could influence the identification of the functional flexion axis. The purpose of this study was to analyse the estimation of the functional flexion axis by separately focusing on passive flexion and extension movements and specifically assessing its orientation compared to the transepicondylar axis, in both the axial plane and the frontal plane.

Methods

Anatomical and kinematic acquisitions were performed using a commercial navigation system on 79 patients undergoing total knee arthroplasty with cruciate substituting prosthesis design. The functional flexion axis was estimated from passive movements, between 0° and 120° of flexion and back. Intra-observer agreement and reliability, internal–external rotation and the angle with the surgical transepicondylar axis, in axial and frontal planes, were separately analysed for flexion and extension, in pre- and post-implant conditions.

Results

The analysis of reliability and agreement showed good results. The identification of the functional flexion axis showed statistically significant differences both in relation to flexion and extension and to pre- and post-implant conditions, both in frontal plane and in axial plane. The analysis of internal–external rotation confirmed these differences in kinematics (p < 0.05, between 25° and 35° of flexion).

Conclusions

The identification of the functional flexion axis changed in relation to passive flexion and extension movements, above all in frontal plane, while it resulted more stable and reliable in axial plane. These findings supported the possible clinical application of the functional flexion axis in the surgical practice by implementing navigated procedures. However, further analyses are required to better understand the factors affecting the identification of the functional flexion axis.

Level of evidence

IV.

     

Capacity of young males and females for running in desert heat

Tolerance for sustained activity in the desert at about 40 degrees C was assessed on high school students, mostly athletically oriented and scholastically superior. The 14 males compared with the 12 females had an aerobic capacity greater by about one-half and a percentage of body fat smaller by about one-half. Each sex attained about the same percentage of aerobic capacity in their maximal sustained effort. This involved an increase in metabolic rate of 3 to 5 fold in females and 6 to 8 fold in males. In maximal sustained effort responses of males and females were alike in respect to rectal and skin temperatures and heart rate. At a rate at which nearly all walked for one hour, 100 m/min, there were no significant differences in metabolic rate, sweat rate nor in composition of sweat. Running at 120 m/min required maximal effort by most females; their maximal sweat rates ranged from 7.4 to 14.2 ml/m2.min. Most males were able to run at 160 m/min for one-half hor to one hour; their maximal sweat rates ranged from 11.3 to 14.6 m/m2.min. Superior capacity of males over females for sustained exercise in desert heat is related to their higher aerobic capacity and not to a difference in capacity for thermoregulation.     

Functional eccentric-concentric ratio of knee extensors and flexors in pre-pubertal children, teenagers and adult males and females

The purpose of this study was to examine the age and sex associated differences in the eccentric/concentric functional ratio for the knee. Isokinetic concentric and eccentric knee extension and flexion was measured at 0.52 rad x s (-1) and 3.14 rad x s (-1) in 121 subjects. Other than mass there were no significant age-by-sex interaction effects for all variables examined. A significant velocity-by-age group effect was demonstrated for ECC (KF)/CON (KE) with higher ratios at 3.14 compared to 0.52 rad x s (-1). Females' CON (KF)/ECC (KE) was significantly lower than males at both velocities. Adults demonstrated significantly lower CON (KF)/ECC (KE) than the teenagers at 0.52 rad x s (-1) and lower than the prepubertal and teenager groups at 3.14 rad x s (-1). However, for ECC (KF)/CON (KE) at 3.14 rad x s (-1), prepubertal ratios were significantly lower than teenagers and adults. The results of the current study suggest that functional rather than conventional ratio should be used when examining knee stability. During fast velocity movements, prepubertal children have a lower capacity for generating eccentric compared to concentric torque. The lower CON (KF)/ECC (KE) ratio in adults appears to be due to a greater ability to generate large eccentric torques at all slow and fast movement velocities. The lower CON (KF)/ECC (KE) ratio in females is a product of lower concentric torque as opposed to high eccentric torque producing capability as previously thought.     

Mechanomyography and electromyography during and after fatiguing shoulder eccentric contractions in males and females

The aim of this study was to investigate changes in mechanomyographic (MMG) and the surface electromyographic (EMG) signals during and after fatiguing shoulder eccentric contractions in a group consisting of 12 males and 12 females. Exerted force, MMG, EMG, pain and rate of perceived exertion were assessed before, during and after repeated high-intensity eccentric exercises. Bouts of eccentric contractions caused a decrease in the exerted force for males (P<0.05) and an increase in the rate of perceived exertion and pain for both genders (P<0.05). During eccentric exercise, the root mean square (RMS) values of the MMG signal increased (P<0.05). The mean power frequency (MPF) values of the EMG signal decreased at the end of each eccentric bout for both genders (P<0.05); the decrease was higher for females compared with males (P<0.05). Immediately after eccentric exercise in static abduction of the upper limbs, the MMG RMS and MPF values increased (P<0.05). The present study showed that (1) neuromuscular changes associated with pain and changes in muscle stiffness and (2) changes in motor units strategy during fatigue development in shoulder muscle are reflected in the MMG and EMG signals.     

Eccentric and concentric torque-velocity characteristics, torque output comparisons, and gravity effect torque corrections for the quadriceps and hamstring muscles in females

The purpose of this study was to assess and compare eccentric (ECC) and concentric (CONC) torque output of the quadriceps and hamstring muscles and to analyze the effect of gravity effect torque (GET) correction on the calculation of the hamstring/quadriceps peak torque quotient (H/Q quotient). Twenty female subjects performed maximal voluntary CONC and ECC contractions of the quadriceps and hamstring muscles at five isokinetic lever arm velocities from 60 degrees/s to 360 degrees/s. Peak torque was measured and corrected for GET. Mean ECC torque did not significantly change with increasing ECC velocity for either the quadriceps or hamstring muscles (P greater than 0.05). Mean CONC torques were significantly lower than the corresponding ECC torques (P less than 0.05) and decreased with increasing CONC velocity. At each test velocity, the CONC H/Q quotient was significantly lower than the corresponding ECC H/Q quotient (P less than 0.05). Mean H/Q quotients did not significantly change with increasing velocity for either the CONC or ECC tests (means: 0.46 and 0.57; P greater than 0.05). Mean H/Q quotients not corrected for GET significantly increased with increasing velocity for the CONC (0.61 to 0.78; P less than 0.05), but not ECC tests (0.66 to 0.71; P greater than 0.05). The results indicate that the ECC torque-velocity curve is essentially level for both quadriceps and hamstring muscles. The present findings point strongly toward the necessity of correcting for GET when calculating both CONC and ECC H/Q quotients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in lower extremity alignment between males and females. Potential predisposing factors for knee injury

AIM: The goal of this study was to compare measures of lower extremity alignment between males and females, which may account for gender differences in anterior cruciate ligament injury rates. Static lower extremity alignment has been implicated as predisposing individuals to anterior cruciate ligament injury and may vary between males and females. An initial step in identifying relevant risk factors for injury is to determine those factors that vary between genders. METHODS: Thirty male and 27 female college aged individuals with no history of lower extremity injury participated. Three indices of lower extremity alignment were measured on each subject: quadriceps angle, thigh foot angle, and subtalar joint range of motion ratio. RESULTS: Q-angles in females exceeded values for males by 4.4 degrees (p<0.001). Thigh foot angle for females was 3.6 degrees greater than for males (p=0.020). Subtalar joint movement ratio did not vary between genders (p=0.573). CONCLUSION: Previous research suggests that abnormal alignment may predispose individuals to anterior cruciate ligament injury. The present findings may help to explain the difference in anterior cruciate ligament injury rates between males and females. Any tangible links between lower extremity alignment and anterior cruciate ligament injury rates must be confirmed with prospective studies.     

Decrease of knee flexion torque in patients with ACL reconstruction: combined analysis of the architecture and function of the knee flexor muscles

A decrease of deep knee flexion torque after anterior cruciate ligament (ACL) reconstruction, using a semitendinosus (and gracilis) tendon, has been reported. However, the cause of this weakness remains controversial. Architectural and functional differences in the knee flexor muscles influence this weakness. the fiber length of the semitendinosus, gracilis, semimembranosus, and biceps femoris were directly measured in six human cadavers. The flexion torque and EMG of the hamstrings were measured in both limbs of 16 patients (23±5 years) after ACL reconstruction (12–43 months post-operation), using ipsilateral semitendinosus tendon. Magnetic resonance imagings were taken, over both the thighs of those patients, to measure muscle volume and to confirm a state of semitendinosus tendon regeneration. The position of the musculotendinous junction of the semitendinosus was also analyzed. The fiber length of the semitendinosus and gracilis were three to four times longer than that of the semimembranosus and biceps femoris. The difference of flexion torque between the normal and ACL reconstructed limbs significantly increased as the knee flexion angle increased. The EMG value for the semimembranosus and biceps femoris of both limbs as well as the semitendinosus of the ACL reconstructed limbs, significantly reduced as the knee flexion angle was increased. The volume of the semitendinosus in the reconstructed limb was significantly smaller than in normal limbs. The regeneration of the semitendinosus tendon was confirmed in all subjects, and the musculotendinous junction position of the reconstructed limb in almost all subjects was found in further image from the knee joint space than that for the normal limb. The decrease of deep knee flexion torque, after ACL reconstruction, could be due to the atrophy and shortening of the semitendinosus after its tendon has been harvested, as well as the lack of compensation from the semimembranosus and biceps femoris, due to the architectural differences between the semitendinosus and the semimembranosus and biceps femoris.     

Reproducibility of isokinetic knee eccentric and concentric strength indices in asymptomatic young adults

ObjectiveTo assess the reproducibility of isokinetic eccentric and concentric knee extension and flexion strength indices obtained at two different angular velocities.DesignCohort study.SettingUniversity human performance laboratory.Participants45 healthy physically active young adults (25 males).Main outcome measuresA non reciprocal protocol of concentric and eccentric contractions of the knee extensors and flexors was performed at 30 and 120°/s. Strength indices evaluated included peak moment; dynamic control ratios; and the difference between eccentric and concentric ratio at the two angular velocities.ResultsNo evidence for inter-test bias in any of the strength indices was noted. Measurement precision for peak moment, as quantified using ratio limits of agreement, suggest that scores may be expected to vary up to 15% for the knee extensors in both eccentric and concentric contraction modes. An error of up to 19% was calculated for the peak moment scores of the knee flexors. Intraclass correlation coefficients revealed fairly robust preservation of participants’ rank order for the majority of strength indices (>0.85).ConclusionIsokinetic-related indices of knee muscles performance enable an acceptable level of detection of expected changes in muscular strength parameters as a result of planned interventions.     

Physiological anterior laxity in healthy young females: the effect of knee hyperextension and dominance

Female athletes are more likely to sustain an anterior cruciate ligament (ACL) injury. Knee laxity, hyperextension and limb dominance have been suggested as possible factors contributing to the knee injury. The aims of this study were to investigate the physiological anterior knee laxity between the dominant and non-dominant limb and in healthy young females with and without hyperextension knees. Forty-two healthy young females, 21 with hyperextension knees, were recruited voluntarily for this study. The subjects were tested with KT-2000 knee ligament arthrometer at both knees with flexion 30° to obtain the anterior tibial displacements at loadings of 45, 67, 89 and 134 N. The initial and terminal stiffnesses were further calculated and analyzed to demonstrate the differences in the characteristics of knee laxity between limbs and groups. The results showed that there was no significant displacement difference between hyperextension and non-hyperextension groups. However, different physiological anterior laxities were illustrated for the different limbs and groups. The non-dominant side of the hyperextension group had significantly smaller terminal stiffness than that of the non-hyperextension group. The dominant side of the hyperextension group had larger laxity than the non-dominant side in the higher loading conditions. These findings may explain hyperextension knees are at greater risk of sustaining an ACL injury.     

Isokinetic torque levels for knee extensors and knee flexors in soccer players

The knee extensor and knee flexor strengths were measured isokinetically (30 degrees, 180 degrees/s) and isometrically with a Cybex II device in three groups of male soccer players (national team players, n = 13; division I, n = 15; division IV, n = 180) and a group of nonsoccer players (n = 32). There were difference in strength between soccer players and nonsoccer players and between players from different divisions. Correction for body surface area did not affect the results. The knee flexor/knee extensor ratio (H/Q ratio) was significantly higher for soccer players than for nonsoccer players. The fast-speed/slow-speed ratio for knee extensors was higher for nonsoccer players and for national team players than for players from divisions I and IV.     

Variation in bone mineral content and estimated body fat in young adult females

This study was designed to determine whether variability in bone mineral content (BMC) at the lumbar vertebrae (L2-4), radius shaft (RS), femoral neck, and distal radius can significantly contribute to the variability observed in body density (Db) among 89 females (age = 25.1 +/- 5.3 yr) of varying activity levels and menstrual status. Theoretical differences in Db were calculated at +/- 1 and +/- 2 standard deviations of BMC (SDBMC) for the population as well as for the subgroups: eumenorrheic inactive controls (C), recreational runners (RR), collegiate runners (CR), body builders (BB), swimmers (S), and amenorrheic runners (AR). Multiple regression to predict Db yielded significant coefficients (b) for BMC at L2-4 (b = 0.0190, P less than 0.001) and RS (b = 0.0425, P less than 0.01) when added separately to the sum of four skinfolds (subscapula, abdomen, thigh, calf). The differences in % BFHW at +/- 1 and +/- 2 SDBMC for the sample mean for RSBMC were +/- 1.0% and +/- 2.0%, respectively. Variability in L2-4 contributed differences of +/- 1.3% and +/- 2.6% at +/- 1 and +/- 2 SDBMC. The subgroup % BFHW differences (due to L2-4 and RS combined) ranged from an average overestimation of 1.3% for the AR to an average underestimation of 1.4% for the BB. Estimated mean errors for remaining groups were less than or equal to 0.5%. Individual differences ranged from a 3.3% underestimation (BB) to a 3.0% overestimation (AR).(ABSTRACT TRUNCATED AT 250 WORDS)     

Assessment of craniocervical junction and atlantoaxial relation using metrizamide-enhanced CT in flexion and extension

Metrizamide-enhanced computed tomographic (CT) myelography has made it easier to define the relation of the spinal cord to the vertebral canal. A flexion-extension metrizamide-enhanced CT technique has been developed to study the craniocervical junction that refines evaluation of the relation between the spinal cord and the foramen magnum, atlas, and axis. This technique was used to study 15 adults who had had a structurally normal examination of the upper cervical cord and foramen magnum. The average movement of the upper cervical cord was shown to be 1 mm. The advantages of the flexion-extension metrizamide-enhanced CT examination were evident in 10 other patients who had a variety of craniocervical junction pathologies.     

Relationship among eccentric hip and knee torques, symptom severity and functional capacity in females with patellofemoral pain syndrome

Objective

To determine the relationships between eccentric hip and knee torques, symptom severity and functional capacity in females with patellofemoral pain syndrome (PFPS).

Design

Within-subject correlational study.

Setting

University biomechanics laboratory.

Participants

10 females diagnosed with PFPS.

Main outcome measures

Eccentric strength of the hip abductors and lateral rotators, and knee extensors were assessed using an isokinetic dynamometer. A 10-cm visual analog scale was used to determine usual knee pain in the last week. The Anterior Knee Pain Scale (AKPS) was used to determine the functional capacity of the patients.

Results

The study found that the greater the eccentric knee extensor and hip lateral rotator torques, the higher the functional capacity of the patients (p = 0.02, r = 0.72; p = 0.02, r = 0.72). It was also shown that the greater hip lateral rotator torque, the less the usual pain reported in the last week (p = 0.004, r = −0.84). Despite the lack of statistical significance (p = 0.11), it was also found a modest negative relationship between the eccentric knee extensor torque and the usual pain reported in the last week (r = −0.56) that was considered clinically meaningful (d = 1.4).

Conclusions

This study showed that eccentric knee extensor and hip lateral rotator torques were associated with functional capacity and pain level in females with PFPS. Further investigations should be carried out to verify the effects of an intervention program focused on the eccentric action of these muscles with respect to the symptoms in patients with PFPS.     

Anterior and posterior knee laxity in a young adult Korean population

Purpose  

The purposes of this study were (1) to determine normal anterior and posterior knee laxity in a healthy young adult (20–30 years old) Korean population, (2) to compare knee laxity between the male and female populations, (3) to investigate whether generalized joint laxity affects anterior and posterior knee laxity, (4) to determine side–side differences between right and left knees, and thus, to determine normal values of side–side differences.     

Injury to the anterior cruciate ligament during alpine skiing: a biomechanical analysis of tibial torque and knee flexion angle

BACKGROUND: The anterior cruciate ligament has been shown to be particularly susceptible to injury during alpine skiing. Tibial torque is an important injury mechanism, especially when applied to a fully extended or fully flexed knee. PURPOSE: We wanted to record the forces generated in the anterior cruciate ligament with application of tibial torque to cadaveric knees in different positions. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-seven fresh-frozen cadaveric knees were instrumented with a tibial load cell that measured resultant force in the anterior cruciate ligament while internal and external tibial torques were applied to the tibia at full extension, 90 degrees of flexion, full flexion, and forced hyperflexion. RESULTS: At each knee flexion position, mean force generated by 10 N.m of internal tibial torque was significantly higher than the mean generated by 10 N.m of external tibial torque. Mean forces generated by tibial torque at 90 degrees of flexion were relatively low. During flexion-extension without tibial torque applied mean forces were highest (193 N) when the knee was hyperflexed. CONCLUSIONS: Application of internal tibial torque to a fully extended or fully flexed knee represents the most dangerous loading condition for injury from twisting falls during skiing. CLINICAL RELEVANCE: Understanding of the mechanisms of falls can be used to design better equipment and to better prevent or treat injury.     

Effect of taping the patella on concentric and eccentric torque and EMG of knee extensor and flexor muscles in patients with patellofemoral pain syndrome

The acute effect of patella taping on torque and electromyographic (EMG) activity in maximal voluntary concentric and eccentric action of the knee extensor and flexor muscles in patients with patellofemoral pain syndrome was studied in 48 patients (62 knees). The patients (28 female, 20 male) were tested concentrically and eccentrically on a Kin-Com dynamometer with simultaneous EMG recording with the patella untaped and medially or laterally taped. Patients with clinically normal patellar mobility did not improve their quadriceps performance by taping of the patella: after medial taping they decreased theur muscle torque during concentric work at 60°/s (P<0.05) and eccentric work at 180°/s (P<0.05). After lateral taping they decreased their muscle torque during concentric work at 60°/s (P<0.01), and 180°/s (P<0.05) and eccentric work at both 60°/s (P< 0.01) and 180°/s (P< 0.05). Moreover, these patients also decreased their agonist EMG activity during concentric work at 60°/s (P<0.05) and 180°/s (P<0.05) and their antagonist EMG activity during eccentric work at 60°/s (P<0.01). Patients with a clinical lateral patellar hypermobility increased their knee extensor torque after medial taping at 60°/s during both eccentric work (P<0.01) and concentric work (P<0.05). The greatest improvement in quadriceps performance, however, was in patients with a clinical medial patellar hypermobility. They increased their knee extensor torque after lateral taping during eccentric work at both 60°/s (P<0.001) and 180°/s (P<0.001) and during concentric work at 60°/s (P<0.001). They also increased agonist EMG activity during eccentric work at both 60°/s (P<0.01) and 180°/s (P<0.001) and during concentric work at 180°/s (P<0.05). Patients with both lateral and medial patellar hypermobility increased their knee extensor torque by patellar taping in either direction; after medial taping there was an increase during eccentric work at both 60°/s (P<0.01) and 180°/s (P<0.05) and after lateral taping they also showed an increase during eccentric work at 60°/s (P<0.01). There was a slight decrease in knee flexor torque with either medial or lateral taping in comparison with no taping. Furthermore, there was higher antagonist EMG activity during hamstring measurements when the patella was either medially or laterally taped as opposed to untaped. In all four groups of patients, except for the group with lateral and medial hypermobility, there was a highly significant correlation between patients' own evaluation of the taping and their patellar mobility according to the clinical examination.This study was supported by grants from the Swedish Sports Federation and from Beiersdorf Compancy, Homburg, Germany