Muscle force production during bent-knee,bent-hip walking in humans

Researchers have long debated the locomotor posture used by the earliest bipeds. While many agree that by 3–4 Ma (millions of years ago), hominins walked with an extended-limb human style of bipedalism, researchers are still divided over whether the earliest bipeds walked like modern humans, or walked with a more bent-knee, bent-hip (BKBH) ape-like form of locomotion. Since more flexed postures are associated with higher energy costs, reconstructing early bipedal mechanics has implications for the selection pressures that led to upright walking. The purpose of this study is to determine how modern human anatomy functions in BKBH walking to clarify the links between morphology and energy costs in different mechanical regimes. Using inverse dynamics, we calculated muscle force production at the major limb joints in humans walking in two modes, both with extended limbs and BKBH. We found that in BKBH walking, humans must produce large muscle forces at the knee to support body weight, leading to higher estimated energy costs. However, muscle forces at the hip remained similar in BKBH and extended limb walking, suggesting that anatomical adaptations for hip extension in humans do not necessarily diminish the effective mechanical advantage at the hip in more flexed postures. We conclude that the key adaptations for economical walking, regardless of joint posture, seem to center on maintaining low muscle forces at the hip, primarily by keeping low external moments at the hip. We explore the implications of these results for interpreting locomotor energetics in early hominins, including australopithecines and Ardipithecus ramidus.     

Growth and reproduction of Chelidonichthys lucerna (Linnaeus) (Pisces: Triglidae) in the Gulf of Gabès,Tunisia

Growth and reproduction of Chelidonichthys lucerna is reported from Tunisian waters. A total of 286 specimens was collected from landings of bottom trawlers between January 2003 and November 2004. The total length ranged from 16 to 36 cm in females and from 17 to 26 cm in males. Marginal increment analysis of otoliths showed that the translucent zone was laid from October to May and the opaque zone laid from June to September. Females were from 0.5 to 9 years and males from 1 to 7 years old. Growth parameters of the von Bertalanffy growth function were TL_∞ = 40.26; K = 0.06 and t₀ = ?3.03 in females and TL_∞ = 46.16; K = 0.059 and t₀ = ?1.32 in males. The coefficient of the allometric length–weight relationships differed significantly by sex. Females with mature gonads were observed between October and May, with peaks in January and February. Length at which 50% of specimens were mature was 21.6 cm TL (estimated age about 3 years) in females and 19.2 cm TL (estimated age about 1.5 years) in males.     

The taxonomic distinctness of coastal bottom-dwelling fish communities of the North-east Atlantic

1. New techniques for identifying the average taxonomic range of species assemblages were applied to an extensive dataset of bottom-dwelling fish in the coastal waters of NW Europe. These taxonomic distinctness indices provided much greater resolution than traditional diversity indices as they incorporated information on taxonomic relationships into an index which measures species dominance. Unlike standard measures of species richness and diversity, the mean value of these statistics is independent of sampling effort, and this allows objective comparisons to be made between samples from studies where sampling effort is not standardized.
2. A reduction in the average taxonomic range between the fauna of western waters of the UK and that of the southern North Sea was consistent with the general decline in species richness observed between these regions, and suggests that these two factors may be spatially positively correlated. Indices calculated for individual samples of fish on a local scale, however, did not all fit this trend.
3. Much of the variability in taxonomic diversity within the coastal waters of NW Europe was caused by the variable geographical distribution of the elasmobranchs. Of all the families which comprise the fish communities, this group has life-history characteristics which make it most susceptible to impact by commercial trawl fisheries.
4. The use of taxonomic distinctness measures provided additional insights, of relevance to biodiversity assessment, suggesting that they might usefully be applied to other aquatic and terrestrial fauna.     

Individual muscle contributions to the axial knee joint contact force during normal walking

Muscles are significant contributors to the high joint forces developed in the knee during human walking. Not only do muscles contribute to the knee joint forces by acting to compress the joint, but they also develop joint forces indirectly through their contributions to the ground reaction forces via dynamic coupling. Thus, muscles can have significant contributions to forces at joints they do not span. However, few studies have investigated how the major lower-limb muscles contribute to the knee joint contact forces during walking. The goal of this study was to use a muscle-actuated forward dynamics simulation of walking to identify how individual muscles contribute to the axial tibio-femoral joint force. The simulation results showed that the vastii muscles are the primary contributors to the axial joint force in early stance while the gastrocnemius is the primary contributor in late stance. The tibio-femoral joint force generated by these muscles was at times greater than the muscle forces themselves. Muscles that do not cross the knee joint (e.g., the gluteus maximus and soleus) also have significant contributions to the tibio-femoral joint force through their contributions to the ground reaction forces. Further, small changes in walking kinematics (e.g., knee flexion angle) can have a significant effect on the magnitude of the knee joint forces. Thus, altering walking mechanics and muscle coordination patterns to utilize muscle groups that perform the same biomechanical function, yet contribute less to the knee joint forces may be an effective way to reduce knee joint loading during walking.     

The use of passive integrated transponder systems (PIT) triggered by infrared-gates for behavioural studies in nocturnal, bottom-dwelling fish species

The movements of juvenile burbot Lota lota were monitored continuously with an overall efficiency of 92·5%. The results show that passive integrated transponder (PIT) systems (or variations of them) are highly valuable for behavioural studies of small nocturnal fish species at the laboratory or mesocosm scale.     

Ground reaction force estimation using an insole-type pressure mat and joint kinematics during walking

Kinetic analysis of walking requires joint kinematics and ground reaction force (GRF) measurement, which are typically obtained from a force plate. GRF is difficult to measure in certain cases such as slope walking, stair climbing, and track running. Nevertheless, estimating GRF continues to be of great interest for simulating human walking. The purpose of the study was to develop reaction force models placed on the sole of the foot to estimate full GRF when only joint kinematics are provided (Type-I), and to estimate ground contact shear forces when both joint kinematics and foot pressure are provided (Type-II and Type-II-val). The GRF estimation models were attached to a commercial full body skeletal model using the AnyBody Modeling System, which has an inverse dynamics-based optimization solver. The anterior–posterior shear force and medial–lateral shear force could be estimated with approximate accuracies of 6% BW and 2% BW in all three methods, respectively. Vertical force could be estimated in the Type-I model with an accuracy of 13.75% BW. The accuracy of the force estimation was the highest during the mid-single-stance period with an average RMS for errors of 3.10% BW, 1.48% BW, and 7.48% BW for anterior–posterior force, medial–lateral force, and vertical force, respectively. The proposed GRF estimation models could predict full and partial GRF with high accuracy. The design of the contact elements of the proposed model should make it applicable to various activities where installation of a force measurement system is difficult, including track running and treadmill walking.     

The 3D path of body centre of mass during adult human walking on force treadmill

Three-dimensional (3D) path of the body centre of mass (CM) over an entire stride was computed from ground reaction forces during walking at constant average speed on a treadmill mounted on 3D force sensors. Data were obtained from 18 healthy adults at speeds ranging from 0.30 to 1.40 m s^?1, in 0.1 m s^?1 increments. Six subsequent strides were analyzed for each subject and speed (total strides=1296). The test session lasted about 30 min (10 min for walking). The CM path had an upward concave figure-of-eight shape that was highly consistent within and across subjects. Vertical displacement of the CM increased monotonically as a function of walking speed. The forward and particularly lateral displacements of the CM showed a U-shaped relationship to speed. The same held for the total 3D displacement (25.6–16.0 cm, depending on the speed). The results provide normative benchmarks and suggest hypotheses for further physiologic and clinical research. The familiar inverted pendulum model might be expanded to gyroscopic, “spin-and-turn” models. Abnormalities of the 3D path might flag motor impairments and recovery.     

Effect of unilateral load carriage on postures and gait symmetry in ground reaction force during walking

Unilateral load carriage is more hazardous to the musculoskeletal system than bilateral load. The purpose of this study was to examine the effect of such asymmetric carriage on postures and gait symmetry in ground reaction force (GRF) during walking. Kinematics and GRF of 19 adults were recorded while they walked under five load conditions: no load, dumbbell (10 and 20% body weight) held in right and left hand, respectively. After loading, the trunk bent towards the loaded or unloaded side in right- and left-hand trials and under different load weight conditions. The amplitude of trunk bend increased with load, accompanied by decreased stride width, progressively inclined legs towards unloaded side and higher level of asymmetry in medial/lateral GRF (GRFm/l) and free vertical moment GRF (GRFm). The findings indicate the postural adjustment is likely related to the characteristics of load and the task experience and handedness of subject and the unilateral load increases the gait asymmetry in GRFm/l and GRFm.     

Pattern of anterior cruciate ligament force in normal walking

The goal of this study was to calculate and explain the pattern of anterior cruciate ligament (ACL) loading during normal level walking. Knee-ligament forces were obtained by a two-step procedure. First, a three-dimensional (3D) model of the whole body was used together with dynamic optimization theory to calculate body-segmental motions, ground reaction forces, and leg-muscle forces for one cycle of gait. Joint angles, ground reaction forces, and muscle forces obtained from the gait simulation were then input into a musculoskeletal model of the lower limb that incorporated a 3D model of the knee. The relative positions of the femur, tibia, and patella and the forces induced in the knee ligaments were found by solving a static equilibrium problem at each instant during the simulated gait cycle. The model simulation predicted that the ACL bears load throughout stance. Peak force in the ACL (303 N) occurred at the beginning of single-leg stance (i.e., contralateral toe off). The pattern of ACL force was explained by the shear forces acting at the knee. The balance of muscle forces, ground reaction forces, and joint contact forces applied to the leg determined the magnitude and direction of the total shear force acting at the knee. The ACL was loaded whenever the total shear force pointed anteriorly. In early stance, the anterior shear force from the patellar tendon dominated the total shear force applied to the leg, and so maximum force was transmitted to the ACL at this time. ACL force was small in late stance because the anterior shear forces supplied by the patellar tendon, gastrocnemius, and tibiofemoral contact were nearly balanced by the posterior component of the ground reaction.     

Diet of Chelidonichthys obscurus and Chelidonichthys lastoviza (Pisces: Triglidae) from the Gulf of Gabes (Tunisia)

The most common gurnard species in the Gulf of Gabes (Tunisia) are Chelidonichthys lastoviza and C. obscurus. These two species were collected by trawl nets between February 2000 and July 2002 at depths ranging from 80 to 150 meters. In the laboratory the stomach contents were examined for diet assessment and to determine diet variation in relation to fish size, season and sex. The importance of different prey items was analysed utilising several feeding indexes, while diet overlap was tested using Schoener's index and the null model test. The two species showed similar diets, with the same qualitative and quantitative composition. Basic food consisted of crustaceans, mostly mysids and decapods. For Chelidonichthys lastoviza:Gastrosaccus sp. (F = 48.57%), Anchialina agilis (F = 30.57%) and Sicyonia carinata (F = 21.71%); for Chelidonichthys obscurus:Gastrosaccus sp. (F = 80.95%), A. agilis (F = 55.41%) and Pontocaris lacazei (F = 15.15%). A change in food composition based on fish size was observed in both species: mysids more frequently in the diet of small specimens, and decapods in the largest fishes. Seasonal variation in their diet was also recorded. The two fishes showed a significantly higher number of empty stomachs in late autumn and winter. Regardless of species and size class, a biologically significant diet overlap was observed between C. lastoviza and C. obscurus. This result may indicate a lack of competition among triglid species size‐class combinations or strong competition that has not yet led to resource portioning.     

Dynamics of primate bipedal walking as viewed from the force of foot

Bipedal walking of the six species of anthropoid primates including man were examined by means of the force plate technique. Though each species has a particular pattern of bipedal walking, we can classify two types of patterns in these primates as far as the foot force is concerned. The first type includes the man, chimpanzee, and spider monkey and the second type contains the Japanese monkey, hamadryas baboon, and gibbon. It was emphasized that the similarity of man to the chimpanzee and spider monkey in bipedal walking has some evolutionary significance.     

Evidence for chromosomal replicons as units of sister chromatid exchanges

Chromosomal replicons have been described as the cytological counterpart of DNA replicon clusters and have previously been studied in vitro using premature chromosome condensation-sister chromatid differentiation (PCC-SCD) techniques. Chromosomal replicons are visualized as small SCD segments in S-phase cells, and measurement of these segments can provide estimates of relative chromosomal replicon size corresponding to DNA replicon clusters functioning coordinately in S-phase. Current hypotheses of sister chromatid exchange (SCE) formation postulate that sites of SCE induction are associated with active replicons or replicon clusters. We have applied the PCC-SCD technique to in vivo studies of mouse bone marrow cells that have been treated with cyclophosphamide (CP) for two cell cycles. We have been able to visualize chromosomal replicons, as well as SCEs which have been induced in vivo by CP treatment, simultaneously in the same cells. Chromosomal replicons visualized as small SCD segments were measured in PCC cells classified at early or late S-phase based on SCD segment size prevalence. Early S-phase (E/S) PCC cells contained 90% of the SCD segments measured clustered in a segment size range of 0.1 to 0.8 m with a peak value around 0.3 to 0.6 m regardless of CP treatment. As the cells progressed through S-phase, late S-phase (L/S) PCC cells were characterized by the appearance of larger SCD segments and even whole SCD chromosomes in addition to small SCD segments. A concentration of units around 0.4 to 1.0 m was found for L/S SCD segment size distributions regardless of CP treatment with an apparent bimodal profile. Our in vivo data support the existence of a subunit organization of chromosomal replication with a basic functional unit being 0.3 to 0.6 m in size. In addition, we have found that this chromosomal unit of replication or chromosomal replicon does not seem to be functionally perturbed by the mutagen CP. We also found that small SCD segments of 0.4 to 0.7 m in length were involved in the formation of an SCE, suggesting that both spontaneous and CP-induced SCEs occur between chromosomal replicons. These findings provide direct cytogenetic evidence to support a replicon cluster/chromosomal replicon model for SCE formation.     

Eye-scanning during walking in the crabLeptograpsus variegatus

Summary The eyes of the crabLeptograpsus variegatus scan continually when the animal walks. The scanning movements are in the horizontal plane, have an amplitude of between 0.1° and 0.3° and a frequency of about 6 Hz if the animal is surrounded by a bright, contrasting visual field. The scanning movements are abolished if the animal is placed in the dark, or blinded. During scanning the two eyes are predominantly in phase with each other. It is proposed that the scanning is the result of a general increase of activity in the oculomotor neurons during walking, which causes the eyes to oscillate at a frequency which is set by the properties of the optokinetic feedback system. It is suggested that the main function of scanning is to prevent visual adaptation.I thank the members of the Department of Neurobiology for many helpful discussions relating to this study, and Roger Hardie for making the recordings from crab retinula cells, the results of which are referred to in the discussion.     

Biology of the bottom-dwelling shrimp Nauticaris marionis Bate, 1888 at the sub-Antarctic Prince Edward Islands

Sub-Antarctic bottom-dwelling caridean shrimps Nauticaris marionis were collected in April/May between 1984 and 1997 over the shelf region of the Prince Edward Islands (37 °50′E, 46 °45′S). N. marionis is a partially protandric hermaphrodite. Hatching probably occurs just before April each year, but may persist until May. During the 1st year N. marionis seem to survive in undetected localities, moult into juveniles, and then settle amongst the benthos from the plankton beginning probably after November. Diel vertical migration then occurs up to an unknown larger size. The vast majority of juveniles develop into males, most of which transmutate into females by April/May of their 3rd year. Reproduction can occur before all male secondary characteristics have been lost. A minority of individuals develop directly into females without passing through a male phase. Individuals older than 5 years are undetectable using samples of the sizes analysed, but they may well persist in the population. The von Bertalanffy growth parameters for N. marionis are tentatively identified as k=0.2353/year, L _∞=12.6 mm, t ₀=−0.2828 years and WW _∞=2.03 g. Sex-reversal in N. marionis at Marion Island may be affected by the changing environment as sexual differentiation is probably determined during the planktonic stage. Accepted: 3 January 2000     

Antioxidant enzymes in the liver of Chelidonichthys obscurus from the Montenegrin coastline

The activities of antioxidant defence enzymes — total, manganese and copper zinc containing superoxide dismutase (Tot SOD, Mn SOD, CuZn SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and biotransformation phase II enzyme glutathione-S-transferase (GST) — in the liver of longfin gurnard (Chelidonichthys obscurus) from the Montenegrin coastline (Adriatic sea) were investigated. The specimens were collected in winter (February) and late spring (May) at two localities: Platamuni (PL, potentially unpolluted) and the Estuary of the River Bojana (EB, potentially polluted). The obtained results show that the activities of Mn SOD, CAT, GSH-Px and GST in winter were significantly lower at EB than at PL. In spring, the activities of CAT and GST were decreased, while GR activity was increased at EB in comparison to PL. The activities of Mn SOD and GST at PL were decreased and GSH-Px, GR and GST activities at EB were increased in spring compared to winter. Our work represents the first study of liver antioxidant enzymes of longfin gurnard from the Montenegrin coastline and reveals that locality, as a variable, has a greater influence on antioxidant enzymes and biotransformation phase II enzyme GST activities compared to season.