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Results for “Acceleration”

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PubMed2003

[Results of accelerated hyperfractionated radiotherapy in breast conserving therapy: a pilot study].

We performed a pilot study to evaluate the safety, tolerability and clinical usefulness of accelerated hyperfractionated radiotherapy in patients treated with breast conserving therapy (BCT). The radiotherapy was consisted of 1.5 Gy per fraction twice daily to a total dose of 51 Gy to the whole breast with or without 9 Gy boost to the tumor bed in case of positive surgical margin. Thirty-seven patients were treated with accelerated hyperfractionated radiotherapy and 178 patients with conventional radiotherapy between September 1993 and December 1997. Acute or late skin toxicity of Grade 3 or more was not observed. One case of radiation pneumonitis requiring steroid therapy occurred in the conventional group. 8-year local-relapse-free survivals were 100% in accelerated group and 97.0% in conventional group (not significant: p = 0.59). The scores in quality of life at one year after the completion of radiation therapy were not different between the conventional and the accelerated group; symptomatic scores, global QOL scores, and scores by self-estimation for therapy. Admission charges in conventional and in accelerated group were not different, either. These data suggested that accelerated hyperfractionated radiotherapy in BCT was feasible and phase III study to compare conventional with the accelerated hyperfractionated radiotherapy should be planned to evaluate its clinical usefulness in BCT.

Adult↗

PubMed2005

U.S. Food and Drug Administration Drug Approval Summary: conversion of imatinib mesylate (STI571; Gleevec) tablets from accelerated approval to full approval.

UNLABELLED: Imatinib mesylate (Gleevec, Novartis Pharmaceuticals East Manruer, NJ) received accelerated approval on May 10, 2001 for the treatment of patients with chronic myeloid leukemia (CML) in (a) chronic phase after failure of IFN-alpha therapy, (b) accelerated phase, and (c) blast crisis. The accelerated approval was accompanied by a postmarketing commitment by Novartis Pharmaceuticals to continue patient follow-up to determine duration of treatment response and survival. The present review, based on a safety and efficacy report submitted on December 20, 2002, summarizes data applicable to the conversion of these three CML indications to full approval status. RESULTS: Chronic phase CML: Five hundred thirty-two chronic phase CML patients who had not benefited from prior IFN therapy were treated at a starting imatinib mesylate dose of 400 mg p.o. qd; dose escalation to 800 mg p.o. qd was allowed. Patients had received a median of 14 months of IFN therapy at doses > or =25 million IU/wk and were all in late chronic phase, with a median time from diagnosis of 32 months. Median duration of imatinib mesylate treatment was 29 months, with 81% of patients treated for > or =24 months (maximum 31.5 months). Initial favorable treatment responses were sustained. An estimated 87.8% of patients who had a major cytogenetic response maintained their response 2 years after their initial response. After 2 years of treatment, an estimated 85.4% of patients were free of progression to accelerated phase or blast crisis, and the estimated overall survival was 90.8% (95% confidence interval, 88.3-93.2). Accelerated phase CML: Patients enrolled totaled 293: 235 with CML accelerated phase, 48 with relapsed/refractory acute lymphocytic leukemia, 2 with relapsed/refractory acute myelocytic leukemia, and 8 with relapsed/refractory CML in lymphoid blast crisis. Patients received imatinib mesylate 400 or 600 mg p.o. qd. Dose escalation was permitted, to a maximum of 800 mg/d, taken as 400 mg bid. Efficacy results were improved in patients receiving imatinib mesylate 600 mg qd versus patients receiving 400 mg qd. The median duration of hematologic response was 29 versus 17 months and the estimated 24-month maintained hematologic response rate was 61% versus 42%. The median survival of patients treated with imatinib mesylate 600 mg qd was not reached versus 20.9 months for patients receiving 400 mg qd. Estimated 24-month survival rate was 66% versus 46%. The median survival in the advanced leukemia population (acute lymphocytic leukemia, acute myelocytic leukemia, and lymphoid blast crisis) was only 5 months, and only two patients are still on treatment. Blast crisis CML: A total of 260 patients were recruited. The imatinib mesylate dose was initially 400 mg qd (37 patients) but was subsequently increased to 600 mg qd (223 patients). Patients receiving imatinib mesylate 600 mg qd had a higher hematologic response rate than did patients receiving 400 mg (33% versus 16%). Major cytogenetic responses occurred in 15% of the 260 study patients. The overall median survival was 6.9 months: 7.1 months for patients treated with imatinib mesylate 600 mg and 4.7 months for patients receiving imatinib mesylate 400 mg. Estimated 12-month survival rate for all study patients was 32.1% and estimated 24-month survival rate was 18.3%. SAFETY: Imatinib mesylate was generally well tolerated, but relatively frequent reports of common toxicity criteria grade 3/4 neutropenia and thrombocytopenia were encountered. The most frequently reported adverse events included gastrointestinal disturbances, edema, rash, and musculoskeletal complaints. These rarely led to discontinuation of therapy. CONCLUSIONS: The results confirm those of the interim analysis and suggest that imatinib mesylate represents an effective therapeutic agent for the treatment of patients with CML in chronic phase after failure of IFN-alpha therapy, in blast crisis, and in accelerated phase.

Adolescent↗

PubMedDate not supplied

[Fetal movement and heart acceleration behavior in eutrophic and hypotrophic fetuses in the 36th to 40th week of pregnancy].

By means of combined ultrasonic and cardiographic monitoring, the movement and acceleration behaviours of 44 eutrophic fetuses were compared to those of 19 fetuses with body weights between the 6th and 10th weight percentiles according to Kyank and to 21 fetuses with body weight not greater than the 5th weight percentile. The eutrophic fetuses moved more frequently and--related to 10 minutes examination time--over longer total periods than did the fetuses with intrauterine growth retardation. The longest mean duration of isolated fetal movement, however, was observed in the hypotrophic fetuses. With regard to fetal resting and activity stages, the highest percentage (10%) of fetal resting stages was found in the fetuses less than or equal to the 5th weight percentile. 93% of all accelerations in fetal heart rate obviously resulted from fetal movements, duration and amplitude of the accelerations depending on the duration of fetal movements. The degree of heart rate responses to fetal movements was different in the three groups examined. Standard weight fetuses responded most intensively. The percentage of fetal movements resulting in accelerations was highest (76%) in the group of the eutrophic fetuses as well. The mean duration of acceleration was most marked in the group of fetuses less than or equal to the 5th weight percentile (32.8 sec) and so was the mean acceleration amplitude in the normotrophic fetuses (19.7 bpm). Decelerations following accelerations in fetal heart rate did not differ in the three groups examined with regard to their number, amplitude and duration.

Female↗

PubMed1986

Spinal and supraspinal mechanisms for morphine-pentobarbital antinociceptive interaction in relation to cardiac acceleration response in rats.

In rat experiments, morphine-pentobarbital antinociceptive interaction affecting cardiac acceleration in response to somatic noxious stimulation was analyzed with the use of intrathecal and intracerebroventricular injections of morphine. Cardiac acceleration response was induced by tail compression, and heart rate was monitored by electrocardiogram. Pentobarbital, in a subanesthetic intravenous dose, antagonized the antinociceptive effect of morphine in relation to cardiac acceleration response when morphine was administered intracerebroventricularly. Without pentobarbital, morphine, 8 micrograms, almost completely blocked the cardiac acceleration response, which was only 1 +/- 1 beats/min. When pentobarbital (10 mg/kg intravenously) was administered in a combination with the same dose of morphine, the cardiac acceleration response was 29 +/- 3 beats/min (P less than 0.0001). In contrast, when morphine was administered intrathecally, the antagonism by pentobarbital of the cardiac acceleration response was absent. The results suggest that supraspinal mechanisms play a decisive role in morphine-pentobarbital antagonism in relation to cardiac acceleration response to somatic noxious stimulation.

Animals↗

PubMed1983

The relation between fetal heart rate accelerations and fetal movements.

Fetal heart rate (FHR) accelerations associated with fetal movements is considered a sign of fetal well-being. Fetal movements as felt by the pregnant woman and visualized by real-time ultrasonography were correlated to FHR accelerations in 52 normal and high-risk pregnant women. All fetal movements felt by the mother or seen in the real-time ultrasonography were associated with large FHR accelerations (more than 15 beats per minute lasting 15 seconds or more) or small accelerations (fewer than 15 beats per minute). The large accelerations were associated with 78.6% of fetal movements felt by the mother and 99.6% of fetal movements seen by real-time ultrasonography. The small accelerations were associated with 52.9% of fetal movements felt by the mother and 82.4% of fetal movements seen by ultrasonography. Mothers felt 75.7% of fetal movements seen by real-time ultrasonography. It was concluded that fetal movements could be verified by existence of large accelerations on the FHR tracing.

Female↗

PubMed1980

[The clinical significance of accelerations in intrapartum fetal heart rate monitoring (author's transl)].

Fetuses failing to exhibit accelerations in antepartum fetal heart rate (FHR) testing are considered to be at risk. However, until now the prognostic value of intrapartum FHR-accelerations is not known. The occurrence or absence of accelerations during the last 30 minutes preceding delivery was compared in 812 intrapartum FHR-records with FHR-score (3), umbilical cord artery pH, one and five minute Apgar score values. When accelerations were absent during the last 30 minutes before delivery, severe neonatal depression was observed in 10 per cent of neonates as compared to 5 per cent when accelerations were present. This difference is statistically significant. If accelerations were observed, no correlation was found between rate of FHR increase, amplitude, or duration of accelerations, and fetal or neonatal state.

Apgar Score↗

PubMed1996

Acceleration of influenza virus clearance by Th1 cells in the nasal site of mice immunized intranasally with adjuvant-combined recombinant nucleoprotein.

The protective roles of influenza viral nucleoprotein (NP), together with the cellular mechanism of the protection in the nasal site, were examined in BALB/c mice immunized intranasally with an adjuvant (cholera toxin B subunit containing 0.2% of the whole toxin)-combined A or B virus recombinant NP. The NP-immune mice, when challenged intranasally with a sublethal dose of the virus 3 wk after immunization, had accelerated virus clearance from the nasal site in both an influenza type-specific and a nonspecific manner, as shown by the protection from high morbidity from the second day after challenge. Both type-specific and nonspecific acceleration of recovery was confirmed by the increased survival rate after challenge with a lethal dose of virus in mice immunized and boosted with adjuvant-combined NP. The acceleration of nasal virus clearance was accompanied with acceleration of type-specific systemic delayed-type hypersensitivity (DTH) and with IFN-gamma production by nasal lymphocytes. The nasal lymphocytes from the immunized and challenged mice generated a significantly high level of DTH when transferred locally, but no class I MHC-restricted CTL response. Moreover, nasal CD4+ T cells, induced by NP immunization and increased in number by the subsequent challenge, were involved in the accelerated IFN-gamma production. These results suggest that nasal Th1 cells, capable of producing IFN-gamma and mediating DTH, are involved in the type-specific acceleration of recovery from influenza after challenge in mice immunized intranasally with adjuvant-combined NP, although the nonspecific mechanism of accelerated recovery remains to be solved.

Adjuvants, Immunologic↗

PubMed1990

Muscle activities during asymmetric trunk angular accelerations.

The objective of this study was to characterize trunk muscle and intra-abdominal pressure behavior during extensions of the trunk when angular trunk acceleration levels and trunk twist were varied during lifting exertions. Since force is related to acceleration, it was believed that changes in trunk acceleration would cause activity changes in the muscles and abdominal cavity pressurization mechanics that load the spine during manual materials handling tasks. The electromyographic activity of 10 trunk muscles and intra-abdominal pressure were studied in 39 subjects as they moved their trunks under high, medium, and low constant angular acceleration conditions. The results indicated that almost all the muscles were affected by acceleration and asymmetry. Muscle activities of up to 50% of maximum were observed even though a minimal amount of torque was being produced by the back. Coactivation of muscles was also apparent. Muscles located at the greatest distances from the spine, such as the latissimus dorsi and oblique groups, increased their activities the most as trunk acceleration increased. Muscles located farthest from the spine also played an important role as the trunk became more asymmetric. Intra-abdominal pressure changed minimally over the test conditions. The nature of these responses and their impact on spine loading are discussed.

Acceleration↗

PubMed1991

Otolith-visual interaction in the control of eye movement produced by sinusoidal vertical linear acceleration in alert cats.

1. Eye movement responses were examined in alert cats during sinusoidal vertical linear acceleration. Stimulus frequencies of 0.20-0.85 Hz with a constant amplitude of 10.5 cm (corresponding to 0.02-0.31 g) were used. A random visual pattern was presented to give sinusoidal vertical optokinetic stimuli of similar amplitude and frequency to the up-down motion of the cat. 2. Sinusoidal linear acceleration in the presence of a stationary visual pattern produced robust eye movement responses with near compensatory phase at all stimulus frequencies tested. With both eyes covered, a vertical linear vestibulo-ocular reflex (LVOR) was frequently produced at a stimulus strength corresponding to 0.04-0.31 g. The evoked LVOR was always small, and the overall mean response phase values advanced by as much as 70 degrees at frequencies below 0.56 Hz, indicating that the otolith signals activated by sinusoidal linear acceleration were not, by themselves, converted into compensatory eye position signals under these experimental conditions. 3. Optokinetic stimulation alone produced more lag of response phase as stimulus frequency increased, and the gain of evoked eye movement responses was smaller at higher stimulus frequencies compared to the gain during linear acceleration in the light. Bilateral labyrinthectomies resulted in a significant change of the eye movement responses during linear acceleration when visual inputs were allowed: there was more phase lag at higher stimulus frequencies and a decreased gain at all frequencies tested. These results indicate that the interaction of otolith and visual inputs produces robust eye movement responses with near compensatory phase during sinusoidal linear acceleration in the light.

Acceleration↗

PubMed1989

Asymmetric velocity and acceleration profiles of human arm movements.

Displacement, velocity, acceleration and jerk (change of acceleration with time) were analyzed for arm flexion movement over a wide range of movement amplitudes and speeds. Relative time to peak velocity or relative duration of acceleration, k, was approximately 0.5 for the movements with intermediate speed (about 0.5 s in movement time), i.e., symmetric velocity and acceleration profiles. For the slow and ballistic movements, k shifted towards values below and above 0.5, respectively creating asymmetric profiles. Consistent k-dependence of movement time, peak velocity, maximum acceleration and maximum deceleration were observed. "Jerk cost", the square of the magnitude of jerk integrated over the entire movement, was calculated for each movement. A dynamic optimization technique to minimize jerk cost under the constraint on jerk input was applied to interpret the results, assuming that a major goal of skilled movements was to produce optimally smooth movements. The constrained minimum-jerk model explained speed-dependent asymmetry of the velocity and acceleration profiles. Jerk cost consumed by the movements with intermediate speed approximately satisfied minimum-cost criterion predicted by the model but was higher than the criterion for slow and ballistic movements. The results suggested that optimality criteria other than jerk cost also should be considered to predict movement profiles over the entire range of speeds.

Acceleration↗

PubMed2001

Applicability of a mobile accelerator for intraoperative radiation therapy to colorectal cancer.

PURPOSE: Intraoperative radiation therapy is reportedly effective for local control and pain relief in colorectal cancer. However, this treatment requires a large number of medical personnel, which hinders expanded use of this method. A mobile electron linear accelerator for intraoperative radiation therapy has been developed and is now commercially available. This report analyzes the applicability of this accelerator to colorectal cancer. The applicability of the mobile accelerator is analyzed based on its specifications by simulating the intraoperative radiation therapy delivered to these patients with a conventional intraoperative radiation therapy unit. METHODS: From 1987 to 1999, 49 colorectal cancer patients underwent 54 surgical resections and received intraoperative radiation therapy to 75 sites. RESULTS: The mean intraoperative radiation therapy dose for colorectal cancer with the conventional unit was 22 (range, 10-30) Gy. The mean electron energy level was 10 (range, 3-30) MEV. Applicator size ranged from 4 to 10 cm in diameter. The mobile accelerator can achieve a dose rate of 10 Gy/min and an applicator unit size range of 3 to 10 cm in diameter, facilitating intraoperative radiation therapy for colorectal cancer. The electron energy limitation (12 MEV at maximum) suggests that the indications for this machine are limited. In our experience, 30 percent of patients received intraoperative radiation therapy with electron energy levels exceeding 12 MEV. Of these cases, 81 percent had macroscopic residual tumor and 69 percent had pain. CONCLUSION: An intraoperative radiation therapy mobile accelerator can cover 72 percent of the irradiation sites covered using our conventional unit. This accelerator is useful for intraoperative radiation therapy with curative intent for patients with no or slight residual tumor. Patients with gross residual tumor and pain may not be suitable.

Adult↗

PubMed1998

Tilt perception during dynamic linear acceleration.

Head tilt is a rotation of the head relative to gravity, as exemplified by head roll or pitch from the natural upright orientation. Tilt stimulates both the otolith organs, owing to shifts in gravitational orientation, and the semicircular canals in response to head rotation, which in turn drive a variety of behavioral and perceptual responses. Studies of tilt perception typically have not adequately isolated otolith and canal inputs or their dynamic contributions. True tilt cannot readily dissociate otolith from canal influences. Alternatively, centrifugation generates centripetal accelerations that simulate tilt, but still entails a rotatory (canal) stimulus during important periods of the stimulus profiles. We reevaluated the perception of head tilt in humans, but limited the stimulus to linear forces alone, thus isolating the influence of otolith inputs. This was accomplished by employing a centrifugation technique with a variable-radius spinning sled. This allowed us to accelerate the sled to a constant angular velocity (128 degrees/s), with the subject centered, and then apply dynamic centripetal accelerations after all rotatory perceptions were extinguished. These stimuli were presented in the subjects' naso-occipital axis by translating the subjects 50 cm eccentrically either forward or backward. Centripetal accelerations were thus induced (0.25 g), which combined with gravity to yield a dynamically shifting gravitoinertial force simulating pitch-tilt, but without actually rotating the head. A magnitude-estimation task was employed to characterize the dynamic perception of pitch-tilt. Tilt perception responded sluggishly to linear acceleration, typically reaching a peak after 10-30 s. Tilt perception also displayed an adaptation phenomenon. Adaptation was manifested as a per-stimulus decline in perceived tilt during prolonged stimulation and a reversal aftereffect upon return to zero acceleration (i.e., recentering the subject). We conclude that otolith inputs can produce tilt perception in the absence of canal stimulation, and that this perception is subject to an adaptation phenomenon and low-pass filtering of its otolith input.

Acceleration↗

PubMed2001

Perception of tilt (somatogravic illusion) in response to sustained linear acceleration during space flight.

During the 1998 Neurolab mission (STS-90), four astronauts were exposed to interaural and head vertical (dorsoventral) linear accelerations of 0.5 g and 1 g during constant velocity rotation on a centrifuge, both on Earth and during orbital space flight. Subjects were oriented either left-ear-out or right-ear-out (Gy centrifugation), or lay supine along the centrifuge arm with their head off-axis (Gz centrifugation). Pre-flight centrifugation, producing linear accelerations of 0.5 g and 1 g along the Gy (interaural) axis, induced illusions of roll-tilt of 20 degrees and 34 degrees for gravito-inertial acceleration (GIA) vector tilts of 27 degrees and 45 degrees , respectively. Pre-flight 0.5 g and 1 g Gz (head dorsoventral) centrifugation generated perceptions of backward pitch of 5 degrees and 15 degrees , respectively. In the absence of gravity during space flight, the same centrifugation generated a GIA that was equivalent to the centripetal acceleration and aligned with the Gy or Gz axes. Perception of tilt was underestimated relative to this new GIA orientation during early in-flight Gy centrifugation, but was close to the GIA after 16 days in orbit, when subjects reported that they felt as if they were 'lying on side'. During the course of the mission, inflight roll-tilt perception during Gy centrifugation increased from 45 degrees to 83 degrees at 1 g and from 42 degrees to 48 degrees at 0.5 g. Subjects felt 'upside-down' during in-flight Gz centrifugation from the first in-flight test session, which reflected the new GIA orientation along the head dorsoventral axis. The different levels of in-flight tilt perception during 0.5 g and 1 g Gy centrifugation suggests that other non-vestibular inputs, including an internal estimate of the body vertical and somatic sensation, were utilized in generating tilt perception. Interpretation of data by a weighted sum of body vertical and somatic vectors, with an estimate of the GIA from the otoliths, suggests that perception weights the sense of the body vertical more heavily early in-flight, that this weighting falls during adaptation to microgravity, and that the decreased reliance on the body vertical persists early post-flight, generating an exaggerated sense of tilt. Since graviceptors respond to linear acceleration and not to head tilt in orbit, it has been proposed that adaptation to weightlessness entails reinterpretation of otolith activity, causing tilt to be perceived as translation. Since linear acceleration during in-flight centrifugation was always perceived as tilt, not translation, the findings do not support this hypothesis.

Acceleration↗

PubMed1991

Three-dimensional acceleration of the tibia during walking and running.

Measurements of tibial acceleration during walking and running were obtained by means of a triaxial accelerometer. The accelerometer was fixed to the free end of a Steinmann pin inserted into the right tibia of one volunteer subject. The patterns of tibial acceleration showed little step-to-step variation within each experimental condition. Following foot strike and depending upon footwear, the resultant tibial acceleration reached between 2.7 and 3.7 g during walking. The tibia experienced maximal accelerations of 10.6 g during running. The high values of tibial acceleration recorded in the antero-posterior (AP) and medio-lateral (ML) directions clearly revealed the importance of measuring all three components of acceleration to quantify the magnitude of the shock experienced by the lower limbs during locomotor activities.

Acceleration↗

PubMed1994

The relationship between mass and acceleration for impacts on padded surfaces.

It is shown analytically that when an object impacts a deformable surface, the acceleration it experiences is inversely proportional to its mass. This is because acceleration is reduced by deformation of the surface, and more massive objects deform the surface more. Since head injury is thought to depend more on acceleration than applied force, this result implies that children may be at greater risk than adults when striking a padded surface. To test the theoretical prediction, 2.69 and 7.40 kg missiles were dropped 31.8 cm onto three deformable surfaces: dry sod, moist sod, and an artificial playing surface. Impact force was measured with a force plate, and divided by missile mass to obtain acceleration. For each test surface, the smaller mass produced a larger acceleration than the larger mass, confirming the theoretical result. Additionally, load-deformation characteristics of the three surfaces were measured, and the results used to predict the effects of mass on acceleration during impact. The predicted results agreed well with the experimental data for the artificial surface (2.3% difference) and moist sod (5.7% difference), but less well for dry sod (21% difference).

Acceleration↗

PubMed1995

The human ocular torsion position response during yaw angular acceleration.

Recent results by Wearne [(1993) Ph.D. thesis] using the scleral search-coil method of measuring eye position indicate that changes in ocular torsion position (OTP) occur during yaw angular acceleration about an earth vertical axis. The present set of experiments, using an image processing method of eye movement measurement free from the possible confound of search coil slippage, demonstrates the generality and repeatability of this phenomenon and examines its possible causes. The change in torsion position is not a linear vestibulo-ocular reflex (LVOR) response to interaural linear acceleration stimulation of the otoliths, but rather the effect is dependent on the characteristics of the angular acceleration stimulus, commencing at the onset and decaying at the offset of the angular acceleration. In the experiments reported here, the magnitude of the angular acceleration stimulus was varied and the torsion position response showed corresponding variations. We consider that the change in torsion position observed during angular acceleration is most likely to be due to activity of the semicircular canals.

Acceleration↗

PubMed1988

Simulation of launch and re-entry acceleration profiles for testing of shuttle and unmanned microgravity research payloads.

Microgravity experiments designed for execution in Get-Away Special canisters, Hitchhiker modules, and Reusable Re-entry Satellites will be subjected to launch and re-entry accelerations. Crew-dependent provisions for preventing acceleration damage to equipment or products will not be available for these payloads during flight; therefore, the effects of launch and re-entry accelerations on all aspects of such payloads must be evaluated prior to flight. A procedure was developed for conveniently simulating the launch and re-entry acceleration profiles of the Space Shuttle (3.3 and 1.7 x g maximum, respectively) and of two versions of NASA's proposed materials research Re-usable Re-entry Satellite (8 x g maximum in one case and 4 x g in the other). By using the 7 m centrifuge of the Gravitational Plant Physiology Laboratory in Philadelphia it was found possible to simulate the time dependence of these 5 different acceleration episodes for payload masses up to 59 kg. A commercial low-cost payload device, the "Materials Dispersion Apparatus" of Instrumentation Technology Associates was tested for (1) integrity of mechanical function, (2) retention of fluid in its compartments, and (3) integrity of products under simulated re-entry g-loads. In particular, the sharp rise from 1 g to maximum g-loading that occurs during re-entry in various unmanned vehicles was successfully simulated, conditions were established for reliable functioning of the MDA, and crystals of 5 proteins suspended in compartments filled with mother liquor were subjected to this acceleration load.

Acceleration↗

PubMed2004

The effect of localized leg muscle fatigue on tibial impact acceleration.

OBJECTIVE: The objective of this study was to assess the effect of localized leg muscle fatigue on tibial acceleration following impact. BACKGROUND: Peak tibial accelerations measured just distal to the knee joint during running have been shown to increase with general body fatigue. However, the role that local leg muscle fatigue plays in shock attenuation is not clear. METHODS: The unshod, dominant foot of 24 healthy women in two different age groups was impacted into a vertical force plate, using a human pendulum method. Impact velocity and force approximated that found in running. EMG activity of the gastrocnemius and tibialis anterior muscles was monitored during fatiguing isometric exercise to assess fatigue, and quantified at impact as a measure of muscle activation level. A skin-mounted uni-axial accelerometer, was located at the tibial tubercle under pre-load, to measure tibial acceleration at impact. RESULTS: There was a significant decrease in peak tibial acceleration (P = 0.008) and acceleration slope (P = 0.033) following fatigue. There were no significant main effects or interactions for age group or muscle group for all tibial response variables. CONCLUSION: The reduction in peak tibial acceleration following fatigue (for the test performed) is contrary to the response documented following whole-body fatigue.

Acceleration↗