Biomedical subjects

R F Zernicke

Publications and source records attributed to R F Zernicke.

At least 19 recordsLinked to original sources

PubMed1998

Effects of high-fat diet on mature bone mineral content, structure, and mechanical properties.

Diets with a high saturated fat content can produce deleterious effects on the absorption of dietary calcium and consequently an adverse effect on bone mineralization in growing animals. Hence dietary fat may have long-term consequences for skeletal health and skeletal pathologies such as osteoporosis. Whether a diet high in saturated fat has similar negative effects on adult bone, however, remains unresolved. Thus, we investigated effects of a high-fat diet on mature bone structure and mechanics. Adult (40-week-old) roosters were maintained for 20 weeks on either a diet high in saturated fat (HF) or a low-fat (LF) diet. Cortical bone samples (tarsometatarsus) were tested mechanically in three-point bending, and cancellous bone cores from the femoral condyles and tibial plateau (four sites per knee) were tested mechanically in compression. Cortical bone cross-sectional areal data were also compared among the groups, and bone mineral content (BMC) was determined (by ashing) for both cortical bone and cancellous bone samples. There were no significant high-fat diet effects on mature cortical bone mechanical properties, geometric structure, or mineral content. Diet, however, did affect cancellous bone composition. For example, LF cancellous BMC was significantly greater than HF. Mechanical properties of the cancellous bone showed similar trends such that LF cancellous bone strength was consistently greater than HF. The potential for adverse effects of a HF diet on intestinal calcium absorption in the mature animal may be more apparent in cancellous bone, with its faster rate of turnover, than in cortical bone. Changes in cancellous bone structure and mechanical properties, related to dietary saturated fats, may have implications for understanding the role of nutrition in skeletal health and prevention of pathological bone loss (osteoporosis).

Age Factors↗

PubMed1998

Intrinsic muscle properties facilitate locomotor control - a computer simulation study.

The purpose of this study was to investigate, theoretically, to what extent muscle properties could contribute to recovery from perturbations during locomotion. Four models with different actuator properties were created: the FLVT model, which encompassed force-length (FL) and force-velocity (FV) characteristics of human muscles as well as muscle stimulation inputs as functions of time (T); the FLT model, which had muscles without force-velocity characteristics; the FVT model, which had muscles without specific force-length characteristics; and the MT model, which had no muscles but was driven by joint moments (M) as a function of time. Each model was exposed to static and dynamic perturbations and its response was examined. FLVT showed good resistance to both static can dynamic perturbations. FLT was resistant to static perturbation but could not counteract dynamic perturbation, whereas the opposite was found for FVT. MT could not counteract either of the perturbations. Based on the results of the simulations, skeletal muscle force-length-velocity properties, although interactively complex, contribute substantially to the dynamic stability of the musculoskeletal system.

Computer Simulation↗

PubMed1998

Mechanical integrity of subchondral bone in osteochondral autografts and allografts.

OBJECTIVE: To assess the influence of osteochondral graft preservation techniques on post-transplant biomechanics of graft and host subchondral bone in the knee joint. DESIGN: An experimental animal model (sheep), specifically the weight-bearing articular surface of the medial femoral condyle of the knee joints. INTERVENTION: Each sheep received, in the ipsilateral knee, an allograft that was (a) frozen without dimethyl sulfoxide (DMSO), (b) snap-frozen in liquid nitrogen or (c) frozen with DMSO. The contralateral knee received an autograft that was (a) snap-frozen, (b) treated with DMSO or (c) left untreated (fresh). MAIN OUTCOME MEASURES: Mechanical and material properties of bone, including maximal compression stress, modulus of elasticity and bone cores (from the graft centre and surrounding host bone). RESULTS: No significant differences were found in the mechanical properties of the subchondral bone under the graft, but there were significant changes in surrounding bone. Bone surrounding the grafts that were snap-frozen or frozen without DMSO was significantly stronger than the normal control bone. However, bone surrounding fresh autografts and cryoprotected allografts was not significantly different from normal control bone. CONCLUSIONS; The changes in the mechanical behaviour of the host bone may be associated with graft cell viability. The great stiffness of the subchondral host bone may have consequences for long-term graft integrity and for the development of degenerative osteoarthritis.

Animals↗

PubMed1997

Physiological and mechanical adaptations of rabbit medial collateral ligament after anterior cruciate ligament transection.

Progressive physiological and mechanical changes in the medial collateral ligament of the adult rabbit were investigated for as long as 48 weeks after disruption of the anterior cruciate ligament. Eighty-one New Zealand White rabbits were separated into experimental, sham-operated control, and normal control groups. The experimental group underwent unilateral transection of the right anterior cruciate ligament, sham-operated animals served as controls for comparison, and normal animals were evaluated as age-matched, undisturbed (no surgery) controls. Blood flow to the medial collateral ligament (as a physiological measure) and mechanical function (structural and material properties) were assessed at 6, 14, and 48 weeks. The results indicated that loss of the anterior cruciate ligament leads to early mechanical deterioration of the medial collateral ligament with a corresponding loss of physiological homeostasis. Six to 14 weeks after the transection, values for cross-sectional area of the medial collateral ligaments rapidly increased to 1.5 times control values. The ligament became twice as large as the control ligament by 48 weeks. Concomitantly, medial collateral ligament stress at failure of the medial collateral ligament complex decreased rapidly 6-14 weeks after the transection and eventually fell to one-half that of controls by 48 weeks. In terms of low-load behaviour, laxity and load relaxation were significantly greater than that of controls 6 weeks after transection and were further increased by 14 weeks. By 48 weeks, laxity values had recovered somewhat and load-relaxation measures had recovered to near control values. At both 6 and 14 weeks, a statistically significant elevation in blood flow was demonstrated compared with controls. By 48 weeks, however, blood flow was no different from that of the sham-operated control. Thus, early after transection of the anterior cruciate ligament, both low-load and high-load mechanical properties of the medial collateral ligament deteriorated and the rate of blood flow was temporarily elevated. By 48 weeks, blood flow declined to near control values, with a corresponding recovery in viscoelastic behaviour. These findings suggest that, after transection of the anterior cruciate ligament, viscoelastic behaviour of the medial collateral ligament may be related to changes in blood flow and that restoration of normal flow patterns and vascular responses may be linked to the recovery of some low-load mechanical properties in the anterior cruciate ligament-deficient medial collateral ligament.

Adaptation, Physiological↗

PubMed1997

Adaptation of bone to physiological stimuli.

The ability of bone to alter its morphology in response to local physical stimuli is predicated upon the appropriate recruitment of bone cell populations. In turn, the ability to initiate cellular recruitment is influenced by numerous local and systemic factors. In this paper, we discuss data from three ongoing projects from our laboratory that examine how physiological processes influence adaptation and growth in the skeleton. In the first study, we recorded in vivo strains to quantify the locomotion-induced distribution of two parameters closely related to bone fluid flow strain rate and strain gradients. We found that the magnitude of these parameters (and thus the implied fluid flow) varies substantially within a given cross-section, and that while strain rate magnitude increases uniformly with elevated speed, strain gradients increase focally as gait speed is increased. Secondly, we examined the influence of vascular alterations on bone adaptation by assessing bone blood flow and bone mechanical properties in an in vivo model of trauma-induced joint laxity. A strong negative correlation (r2 = 0.8) was found between increased blood flow (76%) in the primary and secondary spongiosa and decreased stiffness (-34%) following 14 weeks of joint laxity. These data suggest that blood flow and/or vascular adaptation may interact closely with bone adaptation initiated by trauma. Thirdly, we examined the effect of a systemic influence upon skeletal health. After 4 weeks old rats were fed high fat-sucrose diets for 2 yr, their bone mechanical properties were significantly reduced. These changes were primarily due to interference with normal calcium absorption. In the aggregate, these studies emphasize the complexity of bone's normal physical environment, and also illustrate the potential interactions of local and systemic factors upon the process by which bone adapts to physical stimuli.

Adaptation, Physiological↗

PubMed1997

Strain gradients correlate with sites of exercise-induced bone-forming surfaces in the adult skeleton.

Physical activity is capable of increasing adult bone mass. The specific osteogenic component of the mechanical stimulus is, however, unknown. Using an exogenous loading model, it was recently reported that circumferential gradients of longitudinal normal strain are strongly associated with the specific sites of periosteal bone formation. Here, we used high-speed running to test this proposed relation in an exercise model of bone adaptation. The strain environment generated during running in a mid-diaphyseal tarsometatarsal section was determined from triple-rosette strain gages in six adult roosters (>1 year). A second group of roosters was run at a high speed (1500 loading cycles/day) on a treadmill for 3 weeks. Periosteal surfaces were activated in five out of eight animals. Mechanical parameters as well as periosteal activation (as measured by incorporated fluorescent labels) were quantified site-specifically in 12 30 degrees sectors subdividing a mid-diaphyseal section. The amount of periosteal mineralizing surface per sector correlated strongly (R2 = 0.63) with the induced peak circumferential strain gradients. Conversely, peak strain magnitude and peak strain rate were only weakly associated with the sites of periosteal activation. The unique feature of this study is that a specific mechanical stimulus (peak circumferential strain gradients) was successfully correlated with specific sites of periosteal bone activation induced in a noninvasive bone adaptation model. The knowledge of this mechanical parameter may help to design exercise regimens that are able to deposit bone at sites where increased structural strength is most needed.

Animals↗

PubMed1997

Administration of systemic matrix metalloproteinase inhibitors maintains bone mechanical integrity in adjuvant arthritis.

OBJECTIVE: To evaluate the influence of systemic tetracycline derived antimetalloproteinase compounds on bone morphology and mechanical integrity. METHODS: Male Lewis rats (n = 78) were randomly assigned to one of 10 groups, comprising controls, adjuvant arthritis (AA), and adjuvant arthritis with various combinations of 2 chemically modified, non-antimicrobial tetracycline derivatives (CMT3 or CMT8) with either of 2 nonsteroidal antiinflammatory agents (flurbiprofen or tenidap). After AA induction (23 days), pharmacological efficacy was assessed by inflammatory indices, body mass changes, joint radiological destruction scores, and pyridinoline collagen derived crosslinks. The structural and material properties of the rat femoral neck were assessed biomechanically. RESULTS: Neither CMT had an antiinflammatory effect, but flurbiprofen and tenidap (alone or together with either CMT) significantly reduced joint inflammation. Pyridinoline excretion increased markedly in untreated AA, but was substantially normalized by either CMT3 alone or by CMT8 with flurbiprofen. AA produced significant deleterious effects on femoral neck structure and mechanical properties. Administration of either CMT, however, had positive effects on the amount of bone and the biomechanical properties of rat femoral neck, but not the mineralization of the bone in the rat femoral neck. CONCLUSION: These data suggest that tetracycline derived antimetalloproteinase compounds can significantly and positively influence bone mechanical integrity associated with inhibition of collagen breakdown.

Animals↗

PubMed1995

Long-term, high-fat-sucrose diet alters rat femoral neck and vertebral morphology, bone mineral content, and mechanical properties.

Short-term exposure to diets high in fat and sucrose can induce hyperinsulinemia, affect calcium and magnesium metabolism, and alter bone mineralization and mechanical properties. The current study focused on the morphological and structural changes that result from long-term exposure to a high-fat sucrose (HFS) diet. Inbred, female Fischer 344 rats were assigned randomly to a low-fat, complex-carbohydrate (LFCC) diet group or a HFS diet for 24 months. At the end of the 2 years, each femoral neck (FN) was tested to failure in cantilever-bending, the sixth lumbar vertebra (L6) was tested in compression, and geometrical characteristics of the bones were determined. Although the HFS rats were significantly fatter and heavier than the LFCC rats, the HFS L6 had a significantly smaller average cross-sectional area. When L6 structural properties were normalised with respect to body mass, the HFS L6 had significantly lower loads, energies, and stiffnesses. The HFS L6 stress and strain energy density values were also significantly less than the LFCC L6. Compared to the LFCC FN, the HFS FN had a smaller cortical shell and larger trabecular core. The HFS FN also had significantly lower mass-normalised loads, energies, and stiffnesses. These results suggest that a long-term HFS diet has a significant adverse effect on rat bone morphology and mechanics.

Adaptation, Physiological↗

PubMed1995

Adaptations of immature trabecular bone to exercise and augmented dietary protein.

Exercise and diet synergistically influence bone, but it remains unclear whether augmenting dietary protein intake during moderate exercise has a beneficial or negative effect on immature bone mechanical integrity. Thus, we examined lumbar vertebral bodies (L6) and femoral necks (FN) in trained and untrained rats fed either a recommended protein (15%) or higher protein (30%) diet. Male Wistar rats (8 wk old) were assigned to one of two exercise groups (high protein exercise [HPE], recommended protein exercise [RPE], run 3 d.wk-1 on a motor-driven treadmill at approximately 80% of their maximum oxygen capacity) or to one of two sedentary caged-control groups (high protein control [HPC], recommended protein control [RPC]. After 8 wk, in the HPE group, FN maximum normal stress was significantly greater than all other groups, and FN maximum load and energy at maximum load (per unit body mass) were significantly greater than the sedentary control groups. L6 stress at the proportional limit and initial-maximum stress did not differ among groups, but L6 percent ash was significantly greater in the HPE and RPC groups. Thus, coupling high dietary protein with moderate exercise can produce positive effects on immature rat femoral neck mechanical properties and structure.

Adaptation, Physiological↗

PubMed1993

Effects of severe diabetes and insulin on the femoral neck of the immature rat.

The interactive effects of severe diabetes and insulin therapy on the geometrical, biomechanical, and histomorphological characteristics of the femoral neck were studied in rats that had streptozotocin-induced, insulin-dependent (Type-I) diabetes. Thirty-six female Sprague-Dawley rats (8 weeks of age) were assigned randomly to one of three groups: 12 to control (C), 12 to severe diabetes mellitus (SDM), and 12 to severe diabetes with insulin treatment (SDI). At the conclusion of 10 weeks, the femoral necks were loaded to failure via cantilever-bending tests, and the geometrical, structural, and material properties of the femoral neck were measured and correlated with fracture-surface cross sections. Decalcified cross sections of the femoral necks were analyzed histomorphometrically to determine the porosity, the bone-cell counts, and the bone spicule/marrow space ratio. Rats with severe insulin-dependent diabetes had significantly lower total body mass than did control rats, as well as significantly less femur mass, femur length, total-bone cross-sectional area, and cortical-shell cross-sectional area. Insulin therapy ameliorated some, but not all, of the detrimental effects of diabetes on femoral neck geometry. Compared with control and SDI rats, SDM rats had lower values for femoral neck structural properties, although differences in structural properties may have been related to retarded growth as well as to diabetes. SDM rats had a significantly lower bone spicule/marrow space ratio and number of osteoclasts than did either the control or SDI rats and had significantly greater porosity in the femoral neck cortex than did control rats. Decrements in femoral neck material properties--which were independent of differences in body size--were significantly and linearly correlated with severity of diabetes (as measured by blood glucose level).

Animals↗

PubMed1993

Gait-related motor patterns and hindlimb kinetics for the cat trot and gallop.

To assess speed- and gait-related changes in semitendinosus (ST) activity, EMG was recorded from three cats during treadmill locomotion. Selected step cycles were filmed, and hip and knee joint kinematics were synchronized with EMG records. Swing-phase kinetics for trot and gallop steps at 2.25 m/s were compared for gait-related differences. Also, swing kinetics for different gallop forms were compared. With few exceptions, ST-EMG was characterized by two bursts for each step cycle; the first preceded paw off (STpo), and the second preceded paw contact (STpc). The two-burst pattern for the walk was defined by a high-amplitude STpo burst and a brief, low-amplitude STpc burst; at the slowest walk speeds, the STpc burst was occasionally absent. For the trot, the STpo burst was biphasic, with a brief pause just after paw off. With increasing walk-trot speeds, the duration of both bursts (STpo, STpc) remained relatively constant, but recruitment increased. Also, the onset latency of the STpo burst shifted, and a greater proportion of the burst was coincident with knee flexion during early swing. At the trot-gallop transition, there was an abrupt change in the two-burst pattern, and galloping was characterized by a high-amplitude STpc burst and a brief, low-amplitude STpo burst. At the fastest gallop speeds, the STpo burst was often absent, and the reduction in or elimination of the burst was associated with a unique pattern of swing phase kinetics at the knee. Knee flexion during the gallop swing was sustained by two inertial torques related to hip linear acceleration (HLA) and leg angular acceleration (LAA); correspondingly, muscle contraction was unnecessary. Conversely, knee flexion at the onset of the trot swing relied on a flexor muscle torque at the knee acting with an inertial flexor torque (LAA). Rotatory and transverse gallops at 4.0 m/s had similar swing phase kinetics and ST-EMG. Gait-related changes in ST-EMG, particularly at the trot-gallop transition, are not congruent with neural models assuming that details of the ST motor pattern are produced by a spinal CPG. We suggest that motor patterns programmed by the spinal CPG are modulated by input from supraspinal centers and/or motion-related feedback from the hindlimbs to provide appropriate gait-specific activation of the ST.

Animals↗

PubMed1993

Dynamics of below-knee child amputee gait: SACH foot versus Flex foot.

Gait kinematics and dynamics during stance of unilateral, below-knee child amputees were analyzed for self-selected, comfortable (0.9 m s-1) and fast (1.3 m s-1) speeds with the SACH foot and the energy-storing Flex-foot prostheses. The three-dimensional movements of the lower limbs were recorded and synchronized with ground reaction forces for 12 subjects (7 girls and 5 boys, ages 6-16 yr). Each lower limb was modeled as a set of interconnected rigid links (thigh, leg, and foot) with frictionless joints (hip, knee, and ankle) to calculate moment and joint power profiles. Marked asymmetries were noted in ground reaction force, joint moment, and power profiles for the prosthetic versus the natural limb, but with the Flex foot the asymmetries were less pronounced than with the SACH foot. For the amputee wearing the Flex foot, greater moments and power were generated by the natural limb at the comfortable pace as compared to the SACH foot, but during fast walking, the SACH foot required greater output from the natural limb. With both prostheses, for the prosthetic limb the amputees used similar force, moment, and power patterns, but with significantly different amplitudes. At both speeds of walking, the Flex foot returned significantly more energy (66% at comfortable and 70% at fast walking) than the SACH foot (21% at comfortable and 19% at fast walking). Thus, the Flex foot had a greater potential for reducing the energy cost of walking at comfortable and fast speeds for the below-knee child amputee.

Adolescent↗

PubMed1993

The transition to reaching: mapping intention and intrinsic dynamics.

The onset of directed reaching demarks the emergence of a qualitatively new skill. In this study we asked how intentional reaching arises from infants' ongoing, intrinsic movement dynamics, and how first reaches become successively adapted to the task. We observed 4 infants weekly in a standard reaching task and identified the week of first arm-extended reach, and the 2 weeks before and after onset. The infants first reached at ages ranging from 12 to 22 weeks, and they used different strategies to get the toy. 2 infants, whose spontaneous movements were large and vigorous, damped down their fast, forceful movements. The 2 quieter infants generated faster and more energetic movements to lift their arms. The infants modulated reaches in task-appropriate ways in the weeks following onset. Reaching emerges when infants can intentionally adjust the force and compliance of the arm, often using muscle coactivation. These results suggest that the infant central nervous system does not contain programs that detail hand trajectory, joint coordination, and muscle activation patterns. Rather, these patterns are the consequences of the natural dynamics of the system and the active exploration of the match between those dynamics and the task.

Arm↗

PubMed1993

Biomechanics and developmental neuromotor control.

By applying the principles and methods of mechanics to the musculoskeletal system, new insights can be discovered about control of human limb dynamics both in adults and infants. Here, we first provide a basic primer about biomechanics--its historical context, terminology, and analytical techniques. Next we review research with animals and human adults that illustrates how limb dynamics provides a window for examining the physical mechanisms underlying neuromotor control. Finally, we elaborate on how our research group has adapted dynamics techniques to investigate how infants gain control of their limbs and learn to reach in the first year of life.

Adult↗

PubMed1992

Mass, center of mass, and moment of inertia estimates for infant limb segments.

To quantify limb dynamics, accurate estimates are needed of anthropometric inertia parameters (mass, center-of-mass location, and moments of inertia). These estimates, however, are not available for human infants; therefore, the movement dynamics of infants have not been studied extensively. Here, regression equations for the masses, center-of-mass locations, and transverse moments of inertia of upper and lower limb segments (upper arm, forearm, and hand; thigh, leg, and foot) of 0.04 to 1.50 yr old infants are provided. A mathematical model of the human body was used to determine the anthropometric inertia parameters for upper limbs in 44 infants and for lower limbs in 70 infants. Stepwise linear regressions were used to fit the distributions of the anthropometric inertia parameters. The regression equations accounted for significant amounts of the variance (64-98%), and the R2-values compared favorably when our equations were cross-validated. Consequently, these regression equations can provide, for infants of similar ages, reasonable estimates of upper and lower limb anthropometric inertia parameters, suitable for equations of motion in the analysis of limb dynamics in human infants.

Anthropometry↗

PubMed1992

Diet-related changes in mechanical properties of rat vertebrae.

High fat and sucrose (HFS) diets may induce glucose intolerance, alter calcium metabolism, and lead to deficits in bone mineralization, development, and mechanical properties. To determine the mechanical and structural consequences of a HFS diet on rapidly growing vertebrae, female Sprague-Dawley rats (8 wk) were assigned randomly (2:1) either to a control group (n = 20) fed a low-fat complex-carbohydrate diet or an experimental group (n = 10) fed a HFS diet for 10-12 wk. The sixth lumbar vertebral body (L6) was isolated from the pedicles, morphological measures were taken, and compression was tested at a fast strain rate, while immersed in a warmed (37 degrees C) isotonic physiological buffer solution. No significant difference in body mass existed between HFS and control groups; nevertheless, HFS L6 cross-sectional areas, lengths, and volumes were significantly smaller than controls. The HFS L6 also had significantly lower mechanical properties, including initial maximum load, energy at initial maximum load, and strain energy density at initial maximum load. Diets high in sucrose and fat content have been associated with changes in calcium metabolism, and the results of the current study suggest that in immature vertebrae, a HFS diet may adversely affect vertebral body mechanical integrity and strength.

Animals↗

PubMed1992

Strenuous exercise-induced remodelling of mature bone: relationships between in vivo strains and bone mechanics.

Mature bone can adapt to strenuous exercise, but no study has correlated the changes in bone in vivo strains, remodelling and mechanical properties that occur as a consequence of strenuous training. Therefore, we examined exercise-related remodelling and in vivo strains in the tarsometatarsus (TMT) of three groups of adult (post-physial closure) White Leghorn roosters: basal control (30 weeks of age), age-matched control (39 weeks) and exercise (39 weeks). Exercise birds ran for 1 h a day, 5 days a week for 9 weeks at 70-75% of predicted maximum aerobic capacity. During treadmill locomotion, in vivo strains were recorded from miniature rosette strain gauges implanted on anterior, medial and lateral TMT cortices. TMT mechanical properties were measured with three-point bending tests to failure. Cortical morphometry was digitized from photographic slides of a 1-mm thick mid-diaphysial cross section of each bone. Exercise and age-matched control TMTs had significantly greater cortical area and maximum load than had basal controls. Exercise axial strains significantly exceeded basal and age-matched control strains along the anterior and lateral surfaces. Age-matched control anterior axial strain was twice that of the basal control. The mature bone remodelling suggested that the structural properties optimized by exercise-induced remodelling may differ from those optimized by age-related remodelling. The findings support the osteoregulatory role of strain but contradict earlier data suggesting that strain magnitudes do not change significantly with age or exercise.

Animals↗

PubMed1991

Coupled and uncoupled limb oscillations during paw-shake response.

Intersegmental limb dynamics and muscle activities were analyzed for consecutive cycles of paw-shake responses from chronic-spinalized cats to investigate how hindlimb trajectories organize into a pattern with regular oscillations, a steady-state response, or alternatively, into a pattern with irregular oscillations, a nonsteady-state response. In the spinalized preparation, steady-state and nonsteady-state responses have an equal likelihood of emerging from the initial cycles of a paw-shake response, suggesting that regular coupling of joint oscillations is not planned by pattern-generating networks within lumbosacral segments. To examine the characteristics of coupled and uncoupled limb oscillations during paw-shake responses, we assessed patterns of muscle activity and hindlimb kinematics of six adult chronic-spinalized cats. Additionally, we used inverse-dynamics techniques to quantify the intersegmental dynamics of the paw, leg, and thigh. Our data indicate that by the second cycle of both steady-state and nonsteady-state responses, the basic pattern of interaction between muscle and motion-dependent torques at the ankle and knee joints was established. During subsequent cycles of steady-state responses, a consistent sequence of timing changes occurred, such that, just prior to steady-state oscillations, torque maximums peaked simultaneously at each joint and joint reversals occurred simultaneously. Although nonsteady-state responses showed a similar sequence during beginning cycles, increased ankle muscle and net torques during middle cycles created larger inertial torques at the knee joint that were not counteracted and resulted in irregular and uncoupled knee oscillations. It is likely that neither steady-state nor nonsteady-state oscillations are planned by pattern-generating networks within lumbosacral segments, but that patterns of interjoint coordination emerge from the coupling among oscillators. For paw-shake responses in the spinalized preparation, coupling may depend on interactions between central circuits and motion-dependent feedback that is necessary to stabilize inertial effects due to large ankle joint accelerations.

Activity Cycles↗