Symmetry-based resistance as a novel means of lower limb rehabilitation

Robotic devices hold much promise for use as rehabilitation aids but their success depends on identifying effective strategies for controlling human-robot interaction forces. We developed a robotic device to test a novel method of controlling interaction forces with the intent of improving force symmetry in the limbs. Users perform lower limb extensions against a computer-controlled resistive load. The control software increases resistance above baseline in proportion to lower limb force asymmetry (balance between left and right limb forces). As a preliminary trial to test the device and controller, we conducted two experiments on neurologically intact subjects. In experiment 1, one group of subjects received symmetry-based resistance while performing lower limb extensions (n=10). A control group performed the same movements with constant resistance (n=10). The symmetry-based resistance group improved lower limb symmetry during training (ANOVA, p<0.05), whereas the control subjects did not. In experiment 2, subjects (n=10) successfully used symmetry-based resistance to alter their lower limb force production towards a target asymmetry (ANOVA, p<0.05). These studies suggest that symmetry-based resistance may hold rehabilitation benefits after orthopedic or neurological injury. Specifically, performing strength training therapy with this controller may allow hemiparetic individuals to focus better on increasing strength and neuromuscular recruitment in their paretic limb while experiencing symmetric limb forces.     

The effects of total ankle arthroplasty on postural stability and loading symmetry in quiet stance

Ankle osteoarthritis is a debilitating condition affecting about 1% of the population with approximately 50,000 new instances annually. One treatment is total ankle arthroplasty (TAA), however, its effects on balance are not well understood. This study analyzed balance over a two-year period following TAA. 408 subjects (177 left, 231 right ankles) diagnosed with end-stage ankle osteoarthritis performed quiet standing trials while center of pressure (COP) data were collected. Data were compared across three time points (pre-op, 1-year, and 2-years post-op) and between surgical and non-surgical limbs using a linear mixed model with significance set at P = 0.05. COP excursions in the feet-together condition were not significantly different between limbs after 2 years in anteroposterior or mediolateral directions (P = 0.06, 0.08) after being significantly different between limbs in the anteroposterior (P = 0.014) and mediolateral direction (P < 0.001) pre-op. The vertical ground reaction force significantly decreased across time in the non-surgical limb, while reciprocally increasing in the surgical limb (P < 0.001). After 2 years, no significant difference in vertical ground reaction force between limbs existed (P = 0.20). Limb asymmetry indices decreased at each time point in both conditions (all P < 0.001) and were not significantly different from zero after 2 years in the feet-together condition (P = 0.290). In conclusion, surgical limb balance improved compared to pre-op, resulting in increased symmetry between limbs after 2 years. Vertical ground reaction forces on both limbs converge and limb asymmetry indices approach zero two years post-op. Differences in the COP excursion-loading symmetry relationship between limbs could be useful for identifying instability in other pathologies.     

Kinetic gait analysis in English Bulldogs

Background

Canine breed conformation may interfere with locomotion and may predispose to orthopedic disease. Bulldogs have a high incidence of orthopedic diseases such as hip dysplasia. Kinetic gait analysis provides an objective way to assess and analyze locomotion. The aim of this study was to study the vertical forces of English Bulldogs during walk using a pressure sensitive walkway. We hypothesize that Bulldogs affected by orthopedic diseases have decreased weight bearing and asymmetric locomotion in the limbs despite having mild to no sings during clinical examination. Thirty English Bulldogs were tested. Peak vertical force, vertical impulse, rate of loading, stance phase duration, symmetry index, goniometry and incidence of orthopedic diseases were recorded.

Results

Although none of the dogs showed signs of pain or discomfort upon manipulation of the hip joints, all dogs had radiographic evidences of hip dysplasia and lack of significant peak vertical force, vertical impulse and stance time differences. The dogs had a mean hind limb symmetry index of 19.8 ± 19.5% and rates of loading ranged from 1.0 to 3.1.

Conclusions

Despite the lack of evident decrease in weight bearing, subclinical lameness can be inferred. The examined dogs had a mean hind limb symmetry index of 19.8 ± 19.5%. Symmetry indices reported in dogs free from orthopedic diseases range from 0.3 to 9.6%. Given non-lame dogs are expected to have a symmetry index close to 0%, data from this study suggests that Bulldogs have gait dysfunctions, which translates into hind limb asymmetries and rate of loading was consistent with severe hip dysplasia despite no visible signs of gait dysfunction. Future studies comparing lame and non-lame Bulldogs are warranted.

     

The measurement and lateral comparison of the peak torque caused by the fast abduction exercise of stretched upper extremities in normal and trained adults

The maximal torque effect of the middle portion of action of the deltoid muscle while raising an outstretched upper limb was measured from left and right sides of normal untrained young adults and of the same age elite athletes. Seventeen strongly right-handed untrained males and females and 10 elite tennis players were tested. All participants were required to raise (abduct) one arm (right and then left, or vice versa) as fast as possible with maximal amplitude while standing on an electronic platform scale which measured to 0.001 kg. An assumed force at the centre of mass of the entire upper limb was considered. The force consisted of two components, namely static weight force of the upper limb and a dynamic force component created by upward acceleration of the limb. Using regression equations and scaling methods the static weight of the upper limb was derived and combined with the dynamic component to produce the total force, applied to the centre of mass of the limb. The total force multiplied by the distance from the centre of mass to point of rotation of the limb equated to the torque produced by deltoid muscle. Using video system analyses the angle of abduction was measured for each individual exercise. The additional anthropometrical tests identified proportionality and body mass indices for each participant.

There was no significant difference in dynamic force and torque between left and right limb from the three groups. Sportsmen demonstrated greater lateral abduction when performing the exercise from the dominant side of the body. Sportsmen also demonstrated greater range of abduction, bigger dynamic force and torque on both sides in comparison to untrained adults. Remarkably, the absolute and relative length of arms of athletes were shorter in comparison to untrained males, but the radius of gyration from the stretched upper limb (from its centre of gravity to the shoulder joint) were greater. This phenomenon may be due to distal shifting of the gravity center of the entire upper limb in elite athletes, perhaps, because greater investment of the distal portion of the limb with skeletal muscle tissue.     

Functional foot symmetry and its relation to lower extremity physical performance in older adults: the Framingham Foot Study

BackgroundWhile many studies use gait symmetry as a marker of healthy gait, the evidence that gait symmetry exists is limited. Because gait symmetry is thought to arise through laterality (i.e., limb preference) and affects gait retraining efforts, it is important to understand if symmetry exists during gait in older adults. Therefore, the purpose of this study was to evaluate foot and gait symmetry in the population-based Framingham Foot Study as well as to determine the effects of vertical force symmetry on physical performance measures.MethodsMembers of the Framingham Foot Study were included in this analysis (N=1333). Foot function and force data were collected using the Tekscan Matscan during self-selected gait, with symmetry evaluated using the symmetry index. The short physical performance battery (SPPB) measures of balance, chair stands and gait speed assessed lower extremity physical function. Participants were evaluated using quartiles of gait speed and foot symmetry to determine the effects of symmetry on lower extremity physical function.ResultsIndividuals with faster gait speed displayed greater foot function asymmetry; individuals with ?3.0% to ?9.5% asymmetry in foot function performed better on the short physical performance battery (SPPB). Further, with aging, the degree of asymmetry was reduced.ConclusionsWhile this research suggests that a moderate degree of foot asymmetry is associated with better lower extremity function, the causes of vertical force asymmetry are unknown. Future studies should evaluate the causes of foot asymmetry and should track the changes in symmetry that occur with aging.     

Kinetic asymmetry in female runners with and without retrospective tibial stress fractures

Gait asymmetry may be linked to the tendency for runners to sustain chronic overuse injuries. This paper compares gait asymmetry in female runners who have never sustained a running-related injury to those who have sustained unilateral tibial stress fractures. The symmetry index was used to characterize asymmetry in the kinetics of both subject groups. There were three aims to this study: (1) to report natural levels of asymmetry for healthy, never-injured female runners, (2) to compare asymmetry levels between never-injured runners and those who have sustained stress fractures, and (3) to examine the kinetics between the involved and uninvolved limbs of runners who have sustained stress fractures. In all three aims, peak medial, lateral, braking, vertical impact, and vertical ground reaction forces, average and peak instantaneous vertical loading rates, and peak shock were examined. In the never-injured runner group, natural levels of asymmetry ranged from 3.1% for peak vertical ground reaction force up to 49.8% for peak lateral ground reaction force. Symmetry indices were not significantly different in the runners who had previously sustained stress fractures. The involved limb of the previously injured runners demonstrated higher values for braking and vertical impact ground reaction force and peak shock. Interestingly, these runners appeared to have bilaterally-elevated lateral ground reaction forces and loading rates as compared to the never-injured group, although this was not statistically tested. This suggests that previously injured runners may be closer to the injury threshold and, thus, more susceptible. Asymmetry may simply influence the side on which they become injured.     

Using force sensing insoles to predict kinetic knee symmetry during a stop jump

Knee kinetic asymmetries are present during jump-landings in athletes returning to sport following anterior cruciate ligament (ACL) reconstruction, and are associated with an increased risk for sustaining a second ACL injury. The loadsol® is a wireless load sensing insole that can be used in non-laboratory settings. The purpose of this study was to determine if the loadsol® could be used to predict knee extension moment and power symmetry during a bilateral stop jump task in healthy recreational athletes. Forty-two uninjured recreational athletes completed seven bilateral stop jumps. During each landing, the loadsol® (100 Hz) measured plantar load while 3D ground reaction forces (1920 Hz) and lower extremity kinematics (240 Hz) were collected simultaneously. Peak impact force, loading rate, and impulse were quantified using the loadsol® and peak knee extension moment, average knee extension moment, and total knee work was quantified using the laboratory instrumentation. Limb symmetry indices were quantified for each outcome measure. Multivariate backwards regressions were used to determine if loadsol® symmetry could predict knee kinetic symmetry. Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to determine the agreement and error between predicted and actual knee kinetic symmetry. Loadsol® impulse and peak impact force symmetry significantly predicted kinetic knee symmetry and explained 42–61% of its variance. There was good agreement (ICCs = 0.742–0.862) between predicted and actual knee kinetic symmetry, and the error in the predicted outcomes range from ±18 to ±43. These results support using the loadsol® to screen for kinetic symmetries during landing in athletes following ACL reconstruction.     

Symmetry indices based on accelerometric data in trotting horses

Detection and quantification of lameness in horses consists primarily of a subjective assessment, whereby both intra- and inter-observer disagreements exist, especially with low grade lameness. Therefore, clinically applicable methods are needed for reliable, objective assessments. The aim of this study was to describe three symmetry indices derived from a simple accelerometric method and investigate these in sound trotting horses. The indices describe the overall symmetry of the gait, the symmetry of loads placed on the limbs and the symmetry in timing between left and right steps. These symmetry indices were able to quantify the high degree of symmetry of the trot in sound horses that has been described in earlier studies using other gait analysis methods. Also, we have analysed the variances and have found high repeatability for all three indices.This provides a basis for future investigations of the symmetry indices and their potential for objective detection and quantification of lameness in horses.     

Gait variability and symmetry remain consistent during high-intensity 10,000 m treadmill running

The aim of this study was to analyze changes in gait variability and symmetry in distance runners. Fourteen competitive athletes ran on an instrumented treadmill for 10,000 m at speeds equivalent to 103% of their season’s best time. Spatiotemporal and ground reaction force data were recorded at 1500, 3000, 5000, 7500 and 9500 m. Gait variability and inter-leg symmetry were measured using median absolute deviation (MAD) and the symmetry angle, respectively. There were no overall changes during the running bout for absolute values, symmetry angles or variability, and there were only moderate changes in variability between successive testing distances for three variables. Even with these few changes, variability was low (<4%) at all distances for all variables measured and, on average, the athletes were symmetrical for five of the seven gait variables measured. There were greater mean asymmetry values for flight time (1.1–1.4%) and for impact force (2.0–2.9%), which might have occurred because of muscle latency as the lower limb responded passively to impact during initial contact. Although most athletes were asymmetrical (>1.2%) for at least one variable, no one was asymmetrical for more than four of the seven variables measured. Being asymmetrical in a few variables is therefore not abnormal and not indicative of asymmetrical gait and given many practitioners analyze symmetry (and variability) on an individual, case-study basis, caution should be taken when assessing the need for corrective interventions.     

Effects of retinoic acid on the muscle patterns produced during forelimb regeneration in larval salamanders (Ambystoma)

After systemic treatment with retinoic acid (RA), Ambystoma opacum and A. punctatum larvae regenerated forelimbs with a wide variety of skeletal and gross anatomical abnormalities. Yet the musculatures within the RA-treated limb regenerates were normal even in instances where the cartilages were deformed beyond recognition as components of the limb skeleton. RA is known to induce reduplication of limb structures, sometimes entire segments. When the latter condition occurred in the present study, the corresponding replicates exhibited limb musculatures which were perfect down to minute details, yet of opposite bilateral symmetry. The results attest, firstly, to the independence of myogenesis and chondrogenesis during limb regeneration. Secondly, RA treatment unmasked an otherwise hidden potential within postembryonic salamander limb tissue for the morphogenesis of the contralateral musculature.     

Symmetry and range limits in importance indices

Recently, Mingo has analyzed the properties of I_imp, an importance index, and demonstrated that its range is not symmetrical. While agreeing with this comment, we believe that more light needs to be shed on the issue of symmetry in relation to such indices. Importance indices are calculated using three values: performance of the organism in the absence and in the presence of neighbors and maximum performance of the organism in ideal conditions. Because of this structure, importance indices can hardly ever achieve symmetry along the whole range of potential performances. We discuss the limitation of the symmetry range for different symmetry types and for both additive and multiplicative indices. We conclude that importance indices, as other interactions indices, are practical tools for interpreting ecological outcomes, especially while comparing between studies. Nevertheless, the current structure of importance indices prevents symmetry along their whole range. While the lack of “perfect” symmetry may call for the development of more sophisticated importance metrics, the current indices are still helpful for the understanding of biological systems and should not be discarded before better alternatives are well established. To prevent potential confusion, we suggest that ecologists present the relevant index symmetry range in addition to their results, thus minimizing the probability of misinterpretation.     

HANDEDNESS IN THE BROWN-THROATED PARAKEET ARATINGA PERTINAX EST RELATION WITH SKELETAL ASYMMETRY

Observations on 56 specimens of Aratinga pertinax when bringing food to the beak prove that 28 birds were right-handed while the other 28 were left-handed. A biometric analysis reveals a slight departure from bilateral symmetry in hindlimb bones in close relationship with handedness. In the right-handed birds, there is a significant predominance in the length of the right hindlimb as a whole and all right limb segments. The opposite holds true in left-handed parrots (except for the femur). Right-handed birds are in general more highly asymmetrical than left-handed ones. There is a positive correlation between asymmetry of homologous segments of a pair of limbs and the asymmetry of the other segments of the same pair of limbs. The absence of significant negative correlations between bilateral differences of the different segments of a limb indicates that departures from bilateral symmetry tend to affect the limb as a whole, and thus is not in agreement with the rule of compensating variations.     

Gait synchronized force modulation during the stance period of one limb achieved by an active partial body weight support system

Our purpose was to demonstrate the ability of an actively controlled partial body weight support (PBWS) system to provide gait synchronized support during the stance period of a single lower extremity while examining the affect of such a support condition on gait asymmetry. Using an instrumented treadmill and a motion capture system, we compared gait parameters of twelve healthy elderly subjects (age 65-80 years) during unsupported walking to those while walking with 20% body weight support provided during only the stance period of the right limb. Specifically, we examined peak three-dimensional ground reaction force (GRF) data and the symmetry of lower extremity sagittal plane joint angles and of time and distance parameters. A reduction in all three GRF components was observed for the supported limb during modulated support. Reductions observed in the vertical GRF were comparable to the desired 20% support level. Additionally, GRF components examined for the unsupported limb during modulated support were consistently similar to those measured during unsupported walking. Modulated support caused statistically significant increases in asymmetry for knee flexion during stance (increased 5.9%), hip flexion during late swing (increased 9.1%), and the duration of single limb support (increased 2.8%). However, the observed increases were similar or considerably less than the natural variability in the asymmetry of these parameters during unsupported walking. The ability of the active PBWS device to provide unilateral support may offer new and possibly improved applications of PBWS rehabilitation for patients with unilateral walking deficits such as hemiparesis or orthopaedic injury.     

Brachial and crural indices of European late Upper Paleolithic and Mesolithic humans

Among recent humans brachial and crural indices are positively correlated with mean annual temperature, such that high indices are found in tropical groups. However, despite inhabiting glacial Europe, the Upper Paleolithic Europeans possessed high indices, prompting Trinkaus (1981) to argue for gene flow from warmer regions associated with modern human emergence in Europe. In contrast, Frayer et al. (1993) point out that Late Upper Paleolithic and Mesolithic Europeans should not exhibit tropically-adapted limb proportions, since, even assuming replacement, their ancestors had experienced cold stress in glacial Europe for at least 12 millennia. This study investigates three questions tied to the brachial and crural indices among Late Pleistocene and recent humans. First, which limb segments (either proximal or distal) are primarily responsible for variation in brachial and crural indices? Second, are these indices reflective of overall limb elongation? And finally, do the Late Upper Paleolithic and Mesolithic Europeans retain relatively and/or absolutely long limbs? Results indicate that in the lower limb, the distal limb segment contributes most of the variability to intralimb proportions, while in the upper limb the proximal and distal limb segments appear to be equally variable. Additionally, brachial and crural indices do not appear to be a good measure of overall limb length, and thus, while the Late Upper Paleolithic and Mesolithic humans have significantly higher (i.e., tropically-adapted) brachial and crural indices than do recent Europeans, they also have shorter (i.e., cold-adapted) limbs. The somewhat paradoxical retention of "tropical" indices in the context of more "cold-adapted" limb length is best explained as evidence for Replacement in the European Late Pleistocene, followed by gradual cold adaptation in glacial Europe.     

Kinesiological and kinematical analysis for stroke subjects with asymmetrical cycling movement patterns

This aim of this study is to provide quantitative analyses of asymmetrical movements between affected and unaffected limbs for hemiparetic subjects in a cycling ergometer. To acquire kinesiological and kinematical data, electromyography (EMG) of quadriceps muscles in the both legs as well as crank positions under three cycling workloads were recorded. The symmetry index (SI) was designed to measure the similarity between muscle activities recorded from affected and unaffected limbs. Using kinematical information of the crank position, the cycling unsmoothness (denoted as roughness index, RI) can be derived from the curvature of the instantaneous cycling speed. Thirteen hemiparetic subjects following a cerebrovascular accident (CVA) and eight able-bodied subjects participated in this study. With total symmetry at SI = 1, the average SIs of hemiparetic subjects (0.66 ± 0.18) were significantly lower (p < 0.01) than those of normal subjects (0.91 ± 0.08) but no significant difference found among three workloads. From the average RI, subjects with hemiparesis exhibited less smooth cycling movements compared to normal group (p < 0.01). Non-parametric Friedman and Wilcoxon tests of RIs further indicated that the workload factors are significantly different only for hemiparetic group (p < 0.01). No significant difference between lower workloads in RIs showed that the CVA subjects’ sound side alone can execute most of the cycling load with minimal involvement of the affected side under lower workload condition. When cycling at a heavier load, however, it is essential to force the affected limb to assist in the pedaling, thus accomplishing an effective cycling exercise. By combining these two quantitative indices, we can observe the kinesiological measurement of the symmetry of EMG phasic activities from SI and the kinematical cycling smoothness in a coordinated movement from RI, which could provide a clinical guideline for cycling exercises for hemiparetic subjects.     

Limb bone bilateral asymmetry: variability and commonality among modern humans

Humans demonstrate species-wide bilateral asymmetry in long bone dimensions. Previous studies have documented greater right-biases in upper limb bone dimensions--especially in length and diaphyseal breadth--as well as more asymmetry in the upper limb when compared with the lower limb. Some studies have reported left-bias in lower limb bone dimensions, which, combined with the contralateral asymmetry in upper limbs, has been termed "crossed symmetry." The examination of sexual dimorphism and population variation in asymmetry has been limited. This study re-examines these topics in a large, geographically and temporally diverse sample of 780 Holocene adult humans. Fourteen bilateral measures were taken, including maximum lengths, articular and peri-articular breadths, and diaphyseal breadths of the femur, tibia, humerus, and radius. Dimensions were converted into percentage directional (%DA) and absolute (%AA) asymmetries. Results reveal that average diaphyseal breadths in both the upper and lower limbs have the greatest absolute and directional asymmetry among all populations, with lower asymmetry evident in maximum lengths or articular dimensions. Upper limb bones demonstrate a systematic right-bias in all dimensions, while lower limb elements have biases closer to zero %DA, but with slight left-bias in diaphyseal breadths and femoral length. Crossed symmetry exists within individuals between similar dimensions of the upper and lower limbs. Females have more asymmetric and right-biased upper limb maximum lengths, while males have greater humeral diaphyseal and head breadth %DAs. The lower limb demonstrates little sexual dimorphism in asymmetry. Industrial groups exhibit relatively less asymmetry than pre-industrial humans and less dimorphism in asymmetry. A mixture of influences from both genetic and behavioral factors is implicated as the source of these patterns.     

Achieving bilateral symmetry during vertebrate limb development

While the various internal organs of vertebrates display many obvious left–right asymmetries in their location and/or morphology, external features exhibit a high degree of bilateral symmetry. How this external bilateral symmetry is established during development is largely unknown. In this review, we explore several mechanisms, in place during development, that regulate the final size of the limb. These mechanisms rely on the presence of positive signaling feedback loops during limb bud growth. Through the activity of these signaling loops and their eventual breakdown when the limb bud has reached a certain size, bilateral symmetry can be achieved.     

Kinematic and dynamic gait compensations resulting from knee instability in a rat model of osteoarthritis

Introduction

Osteoarthritis (OA) results in pain and disability; however, preclinical OA models often focus on joint-level changes. Gait analysis is one method used to evaluate both preclinical OA models and OA patients. The objective of this study is to describe spatiotemporal and ground reaction force changes in a rat medial meniscus transection (MMT) model of knee OA and to compare these gait measures with assays of weight bearing and tactile allodynia.

Methods

Sixteen rats were used in the study. The medial collateral ligament (MCL) was transected in twelve Lewis rats (male, 200 to 250 g); in six rats, the medial meniscus was transected, and the remaining six rats served as sham controls. The remaining four rats served as naïve controls. Gait, weight-bearing as measured by an incapacitance meter, and tactile allodynia were assessed on postoperative days 9 to 24. On day 28, knee joints were collected for histology. Cytokine concentrations in the serum were assessed with a 10-plex cytokine panel.

Results

Weight bearing was not affected by sham or MMT surgery; however, the MMT group had decreased mechanical paw-withdrawal thresholds in the operated limb relative to the contralateral limb (P = 0.017). The gait of the MMT group became increasingly asymmetric from postoperative days 9 to 24 (P = 0.020); moreover, MMT animals tended to spend more time on their contralateral limb than their operated limb while walking (P < 0.1). Ground reaction forces confirmed temporal shifts in symmetry and stance time, as the MMT group had lower vertical and propulsive ground reaction forces in their operated limb relative to the contralateral limb, naïve, and sham controls (P < 0.05). Levels of interleukin 6 in the MMT group tended to be higher than naïve controls (P = 0.072). Histology confirmed increased cartilage damage in the MMT group, consistent with OA initiation. Post hoc analysis revealed that gait symmetry, stance time imbalance, peak propulsive force, and serum interleukin 6 concentrations had significant correlations to the severity of cartilage lesion formation.

Conclusion

These data indicate significant gait compensations were present in the MMT group relative to medial collateral ligament (MCL) injury (sham) alone and naïve controls. Moreover, these data suggest that gait compensations are likely driven by meniscal instability and/or cartilage damage, and not by MCL injury alone.     

Hind foot drumming: Morphofunctional analysis of the hind limb osteology in three species of African mole-rats (Bathyergidae)

Hind foot drumming is a form of seismic signaling that plays a vital role in the communication of several Bathyergidae species. Hind foot drumming is initiated by the rapid movement of the whole hind limb by flexion and extension of the hip and knee. This study aimed to determine if morphological adaptations of the hind limb osteology were measurable using established morphometric analyses in two drumming (Bathyergus suillus and Georychus capensis) and one non-drumming (Cryptomys hottentotus natalensis) African mole-rat species. Forty-three linear measurements of the hind limb were taken in 48 limbs (n = 16 limbs per species) and 32 indices were calculated. Mixed model analysis of variance was used to compare the three species and sexes within a species. Thirteen indices had significant differences between species. Eleven indices had significant differences between sexes within a species. Significant differences between the drumming (B. suillus and G. capensis) and the non-drumming species were observed in three indices. The femoral greater trochanter was relatively shorter in the drumming species compared to the non-drumming species, which is proposed to allow for increased hip joint mobility, thereby permitting drummers to move their limbs at the rapid speed required to generate seismic signals. Furthermore, the small in-lever (shorter greater trochanter) may increase the velocity of limb motion. The robust tibias in the drumming species, as indicated by the tibial robustness index, are likely to counter the additional biomechanical load caused by the muscles involved in hind foot drumming. The relatively small hind feet seen in the drumming species allows for reduced limb weight needed for the rapid extension and flexion motion required during hind foot drumming. The significant differences reflected in the hind limb osteological indices between B. suillus and G. capensis and the non-drumming species are indicative of adaptations for hind foot drumming.     

马鞍山遗址出土碎骨表面痕迹的分析

本文对马鞍山遗址 (1990年度) 出土的一千余件碎骨,借鉴中外学者的研究方法,就其表面痕迹作了尝试性的分析。结果发现,尽管痕迹特征标示出有风化、腐蚀、重力等自然营力的作用,以及动物啃咬等后期侵扰,但主要的特征——破碎状况尤其是管状骨骼的破碎程度和人工痕迹的特征——显示出,这些碎骨的产生主要是由于遗址占有者的活动——敲骨吸髓和制作骨制品造成的。由此,进而对遗址占有者的某些行为和遗址形成过程作了探讨。通过碎骨表面痕迹的分析,为该遗址的进一步综合研究提供了有助的资料和证据。