Predicting Cervical Spine Compression and Shear in Helicopter Helmeted Conditions Using Artificial Neural Networks.

OCCUPATIONAL APPLICATIONSMilitary helicopter pilots around the globe are at high risk of neck pain related to their use of helmet-mounted night vision goggles. Unfortunately, it is difficult to design alternative helmet configurations that reduce the biomechanical exposures on the cervical spine during flight because the time and resource costs associated with assessing these exposures in vivo are prohibitive. Instead, we developed artificial neural networks (ANNs) to predict cervical spine compression and shear given head-trunk kinematics and joint moments in the lower neck, data readily available from digital human models. The ANNs detected differences in cervical spine compression and anteroposterior shear between helmet configuration conditions during flight-relevant head movement, consistent with results from a detailed model based on in vivo electromyographic data. These ANNs may be useful in helping to prevent neck pain related to military helicopter flight by facilitating virtual biomechanical assessment of helmet configurations upstream in the design process.

TECHNICAL ABSTRACTBackground: The use of night vision goggles (NVGs) has been linked to a high prevalence of neck pain and injury in military helicopter pilots. Next generation helmet designs aim to mitigate NVG related consequences on cervical spine loading. Currently, in vivo human-participant experiments are required to collect necessary data, such as electromyography (EMG) to estimate joint contact forces in the cervical spine as a result of unique helmet designs. This is costly and inefficient. Digital human models, which provide inverse dynamics, coupled with artificial neural networks (ANNs), can provide a surrogate for musculoskeletal joint modeling to predict joint contact forces.Purpose: We developed ANNs to predict C6-C7 compression and anteroposterior shear during flight-relevant head movements with sufficient sensitivity to differentiate between candidate helmet designs in terms of associated biomechanical exposures.Methods: Motion capture and EMG data were collected from 26 participants who performed flight-relevant reciprocal head movements about pitch and yaw axes while donning one of four helmet configurations. These data were input into an EMG-driven musculoskeletal model of the neck to generate time series of C6-C7 compression and shear. Rotation-specific ANNs were trained to predict the EMG-driven model outputs, given only the head-trunk kinematics and C6-C7 moments as inputs.Results: ANNs for pitch rotations were successful in estimating peak and cumulative compression and shear, with an absolute error that was lower than absolute differences in joint contact forces between relevant helmet conditions. ANNs for yaw rotations were similarly successful in differentiating between C6-C7 compression and cumulative C6-C7 shear, but less so for peak C6-C7 shear.Conclusions: When combined with biomechanical data readily available from digital human modeling software, use of an ANN surrogate for joint musculoskeletal modeling can permit evaluation of joint contact forces associated with novel helmet designs during upstream design. Improved consideration of joint contact forces during a virtual helmet design process will assist in identifying helmet designs that reduce biomechanical exposures of the cervical spine during helicopter flight.

Exploring the prospective efficacy of waste bag-body contact allowance to reduce biomechanical exposure in municipal waste collection.

Municipal waste collectors must avoid bag-body contact, requiring waste bags to be held further from the body. Donning sharps-proof clothing would permit bag-body contact, allowing the bag to be closer to the body, reducing biomechanical exposures. To test this hypothesis, 25 participants loaded waste bags into a simulated garbage truck hopper under two lifting (contact allowed, no contact) and bag mass (7 kg and 20 kg) conditions. Bottom-up rigid-link biomechanical modelling results including peak low back compression force, antero-posterior shear force and peak low back flexion angle were not different between the lifting conditions, but cumulative compression was decreased with bag-body contact, although only at the 20 kg mass. Bag mass had significant effects on outcome measures, causing compression to increase to 4663 (±697) N, exceeding recommended thresholds. Sharps-proof clothing and municipally mandated 23 kg maximum allowable bag mass restrictions may not sufficiently reduce biomechanical exposures to prevent MSD.

Resting MAPK expression in chronically trained endurance runners.

PURPOSE: There is a paucity of research investigating the expression of mitogen-activated protein kinases (MAPK) in chronically trained (CT) athletes. Thus, it is unclear how MAPK may contribute to performance and muscle adaptation in CT subjects. The purpose of this study was to determine MAPK total protein, and phosphorylated expression of extracellular signal-regulated kinases 1 and 2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38-MAPK (p38) between untrained, and chronically trained runners. METHODS: Tissue samples were analysed from sedentary (SED; n = 5) controls and chronically trained runners (CT; n = 5). Resting muscle biopsy samples were analysed for total-MAPK - and ratio of phosphorylated/total (p-MAPK) - ERK1/2, JNK, and p38-MAPK via western blotting. Mann-Whitney U tests and effect sizes were utilized to determine differences in total MAPK protein content and phosphorylation status between SED and CT subjects. RESULTS: There was no difference in total-MAPK expression between SED and CT (p > .05). p-p38-MAPK tended to be greater for CT compared to SED (p = .07). There were moderate effect sizes of decreased pERK/total-ERK (d = -0.69) and increased pJNK/total-JNK (d = 0.54) in CT compared to SED. There was a positive correlation between p-p38-MAPK/total-MAPK and the percentage of type I fibres (r = 0.73, p = .016). CONCLUSION: Contrary to previous studies, chronic endurance training does not greatly influence total MAPK protein expression in chronically trained runners. However, resting phosphorylation of p38-MAPK may contribute to enhanced oxidative metabolism at chronically trained levels. These alterations are likely involved in the different physiological adaptations that occur following long-term training or at highly competitive levels.

Changes in resting mitogen-activated protein kinases following resistance exercise overreaching and overtraining.

PURPOSE: Many physiological maladaptations persist after overreaching and overtraining resistance exercise (RE). However, no studies have investigated changes in mitogen-activated protein kinases (MAPK) after overtraining in humans, despite their critical role regulating exercise-induced muscular adaptations. The purpose of this study was to describe the changes in total and resting phosphorylation status of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun NH2-terminal kinase (JNK) and p38-MAPK following a period of RE overreaching or overtraining. METHODS: Following 2-4 weeks of normal training (low volume/low intensity), two groups of males performed either a high-power overreaching protocol (HPOR n = 6, mean ± SD, age 23 ± 3.4 years, mass 86.5 ± 17.7 kg, height 1.77 ± 0.06 m) or high-intensity overtraining protocol (HIOT n = 8, age 19.8 ± 1.8 years, mass 76.8 ± 6.7 kg, height 1.8 ± 0.06 m). Resting muscle biopsies were obtained at baseline (BL; end of normal training period) and 24 h after the final session of stressful training (i.e., HPOR or HIOT programs). Total MAPK and ratio of phosphorylated/total (p-MAPK)- ERK1/2, JNK, and p38-MAPK were analyzed via western blotting. 2 × 2 (group × time) ANOVA determined differences in MAPK between BL and post-training protocols. RESULTS: Compared to BL, total-ERK increased after HPOR, but decreased after HIOT (p ≤ 0.05). p-ERK1/2/total-ERK increased after HIOT (p ≤ 0.05). The ratio of p-JNK/total-JNK and p-ERK1/2/total-ERK decreased after HPOR (p ≤ 0.05); however, this result was primarily due to increased total MAPK content. p-p38-MAPK decreased after HPOR (p ≤ 0.05). CONCLUSION: Total and p-MAPK are differentially expressed after HPOR and HIOT RE. These changes are likely involved in the maladaptation reported in overreaching and overtraining exercise. This is the first study describing altered MAPK in RE overtrained and overreached humans.

Resting extracellular signal-regulated protein kinase 1/2 expression following a continuum of chronic resistance exercise training paradigms.

Extracellular signal-regulated protein kinase 1/2 (ERK1/2) moderates skeletal muscle growth; however, chronic responses of this protein to unique resistance exercise (RE) paradigms are yet to be explored. The purpose of this investigation was to describe the long-term response of ERK1/2 following circuit weight training (CWT), recreationally weight training (WT), powerlifting (PL) and weightlifting (WL). Independent t-tests were used to determine differences in trained groups compared to sedentary controls. Total ERK1/2 content was lower in PL and WL compared to their controls (p ≤ 0.05). Specific trained groups displayed large (WL: pERK/total-ERK; d = 1.25) and moderate (CWT: total ERK1/2; d = 0.54) effect sizes for altered kinase expression compared to controls. The results indicate ERK1/2 expression is down-regulated after chronic RE in well-trained weightlifters and powerlifters. Lower expression of this protein may be a method in which anabolism is tightly regulated after many years of high-intensity RE.

Data-driven subclassification of speech sound disorders in preschool children.

PURPOSE: The purpose of the study was to determine whether distinct subgroups of preschool children with speech sound disorders (SSD) could be identified using a subgroup discovery algorithm (SUBgroup discovery via Alternate Random Processes, or SUBARP). Of specific interest was finding evidence of a subgroup of SSD exhibiting performance consistent with atypical speech motor control. METHOD: Ninety-seven preschool children with SSD completed speech and nonspeech tasks. Fifty-three kinematic, acoustic, and behavioral measures from these tasks were input to SUBARP. RESULTS: Two distinct subgroups were identified from the larger sample. The 1st subgroup (76%; population prevalence estimate = 67.8%-84.8%) did not have characteristics that would suggest atypical speech motor control. The 2nd subgroup (10.3%; population prevalence estimate = 4.3%-16.5%) exhibited significantly higher variability in measures of articulatory kinematics and poor ability to imitate iambic lexical stress, suggesting atypical speech motor control. Both subgroups were consistent with classes of SSD in the Speech Disorders Classification System (SDCS; Shriberg et al., 2010a). CONCLUSION: Characteristics of children in the larger subgroup were consistent with the proportionally large SDCS class termed speech delay; characteristics of children in the smaller subgroup were consistent with the SDCS subtype termed motor speech disorder-not otherwise specified. The authors identified candidate measures to identify children in each of these groups.

Kansas squat test: a reliable indicator of short-term anaerobic power.

The purposes of this study were to establish stability reliability of a measure of lower-body anaerobic power, the Kansas squat test (KST), and to compare the KST with the commonly used Wingate anaerobic test (WAnT) for lower-body power. Fourteen resistance-trained men (mean ± SD; age = 24.2 ± 3.6 years) performed both the KST and the WAnT twice on separate occasions. The KST consisted of using an external dynamometer to measure mean repetition power while performing 15 repetitions of speed squats using 70% of 1 repetition maximum system mass (barbell + body mass), initiating each repetition at 6-second intervals. Repetition power, mean power for all 15 repetitions, and % fatigue for the KST were all reliable (intraclass correlation coefficient = 0.754-0.937; p ≤ 0.05). There were no differences between tests for the mean power for all repetitions or relative fatigue (p ≤ 0.05) and no significant differences between tests for any individual repetition (test × repetition interaction, p < 0.05). Although absolute values were different (p > 0.05), significant correlations were found between the KST and WAnT for mean (r = 0.752) and maximum (r = 0.775) test powers but not for relative fatigue (r = 0.174). Lactate (HLa) responses were greater for the WAnT compared with the KST. These data indicate that the KST is reliable for resistance-trained men, and that measures of maximum and mean test powers for the KST are highly correlated to those values for the WAnT, but fatigue rates and HLa responses were not correlated. It appears that the KST is a lifting-specific anaerobic power and power endurance test that emphasizes phosphagen metabolism and may be used to assess training-induced changes in lower-body power.

Indirect estimates of jaw muscle tension in children with suspected hypertonia, children with suspected hypotonia, and matched controls.

PURPOSE: In this study, the authors compared indirect estimates of jaw-muscle tension in children with suspected muscle-tone abnormalities with age- and gender-matched controls. METHOD: Jaw movement and muscle activation were measured in children (ages 3 years, 11 months, to 10 years) with suspected muscle-tone abnormalities (Down syndrome or spastic cerebral palsy; n = 10) and controls (n = 11). Two measures were used to infer jaw tension: a kinematic index of mass-normalized stiffness and electromechanical delay (EMD). The kinematic index used video-based kinematics to obtain the slope of the peak velocity-displacement relationship. The EMD was derived from the interval between the onset of suprahyoid muscle activity and the onset of jaw depression. RESULTS: Neither measure differentiated the groups. The kinematic index revealed differences between stressed and unstressed syllables in 3-syllable productions by the participants with cerebral palsy and controls, but not in 2-syllable productions by the participants with Down syndrome and controls. CONCLUSION: This preliminary investigation included the novel application of 2 measures to infer the jaw-muscle tension of children with suspected tone abnormalities. Although the results do not support the hypothesis that suspected muscle-tone abnormalities affect jaw movement sufficiently to influence speech production, considerations for interpreting the findings include methodological limitations and possible compensatory muscle coactivation.

Distinct developmental profiles in typical speech acquisition.

Three- to five-year-old children produce speech that is characterized by a high level of variability within and across individuals. This variability, which is manifest in speech movements, acoustics, and overt behaviors, can be input to subgroup discovery methods to identify cohesive subgroups of speakers or to reveal distinct developmental pathways or profiles. This investigation characterized three distinct groups of typically developing children and provided normative benchmarks for speech development. These speech development profiles, identified among 63 typically developing preschool-aged speakers (ages 36-59 mo), were derived from the children's performance on multiple measures. These profiles were obtained by submitting to a k-means cluster analysis of 72 measures that composed three levels of speech analysis: behavioral (e.g., task accuracy, percentage of consonants correct), acoustic (e.g., syllable duration, syllable stress), and kinematic (e.g., variability of movements of the upper lip, lower lip, and jaw). Two of the discovered group profiles were distinguished by measures of variability but not by phonemic accuracy; the third group of children was characterized by their relatively low phonemic accuracy but not by an increase in measures of variability. Analyses revealed that of the original 72 measures, 8 key measures were sufficient to best distinguish the 3 profile groups.

Hemostasis with a bipolar sealer during surgical correction of adolescent idiopathic scoliosis.

STUDY DESIGN: Retrospective before-after comparison study. OBJECTIVE: The primary aim of this study was to evaluate the effectiveness of a radiofrequency-based bipolar hemostatic sealer during surgical correction of adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA: Spinal reconstructive surgery is commonly associated with excessive blood loss. Perioperative bleeding is of particular concern during correction of AIS, which often requires allogeneic or autologous transfusion. However, there are specific risks and limitations that often preclude the utilization of transfusions. Alternatives include the use of antifibrinolytic drugs and topical fibrin-based and thrombin-based agents, although safety and effectiveness are yet to be fully established. There is a clear need for assessing alternative methods of hemostasis. METHODS: One hundred seventy-six AIS patients undergoing corrective spinal surgery were included in this study. Seventy-six consecutive patients were treated intraoperatively with a standard method of hemostasis consisting of hypotensive anesthesia, thrombin-soaked sponges, and intraoperative blood salvage (Control). Subsequently, an additional 100 consecutive patients were treated after the introduction of a bipolar sealer (Aquamantys 2.3 Bipolar Sealer, Salient Surgical Technologies, Portsmouth, NH). The outcomes of this study were estimated blood loss (total and per level) and transfusion rate. RESULTS: Blood loss was reduced by 57% after the introduction of the bipolar sealer compared with the Control (bipolar sealer: 435±192 mL, Control: 1009±392 mL; P<0.001). There was a statistically significant difference between groups for blood loss per fusion level (bipolar sealer: 39±17 mL, Control: 95±33 mL; P<0.001). Five (6.6%) Control patients required blood transfusions versus none treated with the bipolar sealer (P=0.014). Complication rates were similar between the groups. CONCLUSIONS: These findings suggest that the Aquamantys 2.3 bipolar sealer effectively supports hemostasis and reduces the need for transfusions during surgical correction of AIS.

An examination of the relationships among myosin heavy chain isoform content, isometric strength, and mechanomyographic median frequency.

The purpose of the present study was to determine if the combination of isometric knee extension strength and mechanomyographic (MMG) median frequency (MDF) could be used to estimate the percent (%) myosin heavy chain (MHC) Type II isoform content of the vastus lateralis. Five resistance-trained (mean +/- SD age = 23.2 +/- 3.7 years) and 5 aerobically trained (mean +/- SD age = 32.6 +/- 5.2 years) men volunteered to perform a 6-second isometric maximum voluntary contraction (MVC) of the dominant knee extensors at a joint angle of 90 degrees between the thigh and leg. During the isometric MVC, the surface MMG signal was detected from the vastus lateralis, and the MDF was calculated with the discrete Fourier transform. Following the isometric MVC and MMG measurements, muscle biopsies were taken from the vastus lateralis and analyzed for % MHC Type II isoform content. The results showed that neither isometric knee extension strength nor MMG MDF alone was significantly correlated with the % MHC Type II isoform content. The combination of isometric knee extension strength and MMG MDF, however, explained a significant proportion (i.e., 59.8%) of the variance in % MHC Type II isoform content, with a multiple correlation of R = 0.773 and a standard error of the estimate (SEE) of 15.4%. These findings indicated that a simple, time-efficient, and noninvasive test that simultaneously measures isometric strength and MMG MDF could be useful for estimating the % MHC Type II isoform content in well-trained men.

Mandibular motor control during the early development of speech and nonspeech behaviors.

PURPOSE: The mandible is often portrayed as a primary structure of early babble production, but empiricists still need to specify (a) how mandibular motor control and kinematics vary among different types of multisyllabic babble, (b) whether chewing or jaw oscillation relies on a coordinative infrastructure that can be exploited for early types of multisyllables, and (c) whether the organization of motor control and associated kinematics varies across the nonspeech behaviors that are candidate motor stereotypies for speech. METHOD: Electromyographic signals were obtained from mandibular muscle groups, and associated kinematics were measured longitudinally from a typically developing infant from 9 to 22 months during jaw oscillation, chewing, and several types of early multisyllabic babble. RESULTS: Measures of early motor control and mandibular kinematics for multisyllabic productions indicated task-dependent changes across syllable types and significant differences across babble and nonspeech behaviors. Differences in motor control were also observed across nonspeech behaviors. CONCLUSIONS: Motor control for babble appears to be influenced by the balanced interaction between developing motor and linguistic systems, such that variation in linguistic complexity systematically evinces changes in motor organization apparently to meet these demands. This same effect was noted among chewing and jaw oscillation; task-dependent changes in mandibular control were noted across behaviors.

A nonword repetition task for speakers with misarticulations: the Syllable Repetition Task (SRT).

PURPOSE: Conceptual and methodological confounds occur when non(sense) word repetition tasks are administered to speakers who do not have the target speech sounds in their phonetic inventories or who habitually misarticulate targeted speech sounds. In this article, the authors (a) describe a nonword repetition task, the Syllable Repetiton Task (SRT), that eliminates this confound and (b) report findings from 3 validity studies. METHOD: Ninety-five preschool children with speech delay and 63 with typical speech completed an assessment battery that included the Nonword Repetition Task (NRT; C. Dollaghan & T. F. Campbell, 1998) and the SRT. SRT stimuli include only 4 of the earliest occurring consonants and 1 early occurring vowel. RESULTS: Study 1 findings indicated that the SRT eliminated the speech confound in nonword testing with speakers who misarticulate. Study 2 findings indicated that the accuracy of the SRT to identify expressive language impairment was comparable to findings for the NRT. Study 3 findings illustrated the SRT's potential to interrogate speech processing constraints underlying poor nonword repetition accuracy. Results supported both memorial and auditory-perceptual encoding constraints underlying nonword repetition errors in children with speech-language impairment. CONCLUSION: The SRT appears to be a psychometrically stable and substantively informative nonword repetition task for emerging genetic research and other research with speakers who misarticulate.

A wavelet-based analysis of surface mechanomyographic signals from the quadriceps femoris.

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to examine the MMG responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Fifteen healthy men [age (mean +/- SD): 26.4 +/- 6.1 years] volunteered to perform isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). During each muscle action, surface MMG signals were detected from the VL, RF, and VM and processed with the MMG wavelet analysis. The results show that, for the VL and VM muscles, there was compression of the total MMG intensity spectra toward low frequencies for most force levels above 20% MVC. For the RF, however, the peak of the total MMG intensity spectrum occurred at approximately 30-40 HZ for all force levels. Because the VL, RF, and VM are all innervated by the femoral nerve, the discrepancies among the three muscles for total MMG intensity in each wavelet band may have been due to differences in architecture, muscle stiffness, and/or intramuscular pressure.

Respiratory movement patterns during vocalizations at 7 and 11 months of age.

PURPOSE: The present investigation was designed to study the modulation of abdomen and rib cage movements during vocalization over a period of development associated with rapid decreases in the compliance of the chest wall. METHOD: Rib cage and abdominal kinematics were recorded during spontaneous vocalizations in 7- and 11-month old infants. Principal component analysis was used to represent each infant's abdomen and rib cage traces as the weighted sum of a small number of principal component (PC) waveforms. RESULTS: The fundamental periods of infants' PC waveforms in the 11-month group were significantly shorter than those in the 7-month group. In addition, the variance contributed by PCs describing unidirectional patterns of respiratory movement decreased in the 11-month group, whereas the variances contributed by PCs describing modulated patterns of movement increased. Lastly, the extent to which abdomen and rib cage movements predicted the duration of corresponding vocalizations also increased significantly in the 11-month group compared with the 7-month group. CONCLUSIONS: The findings of the present study were consistent with the hypothesis that decreases in the compliance of the chest wall result in more rapid modulation of chest wall movements and greater control of those movements by the developing neuromuscular system.

Task specificity in early oral motor development.

This article addresses a long-standing clinical and theoretical debate regarding the potential relationship between speech and nonspeech behaviors in the developing system. The review is motivated by the high popularity of nonspeech oral motor exercises (NSOMEs), including alimentary behaviors such as chewing, in the treatment of speech disorders in young children. The similarities and differences in the behavioral characteristics, sensory requirements, and task goals for speech and nonspeech oromotor behaviors are compared. Integrated theoretical paradigms and empirical data on the development of early oromotor behaviors are discussed. Although the efficacy of NSOMEs remains empirically untested at this time, studies of typical developmental speech physiology fail to support a theoretical framework promoting the use of NSOMEs. Well-designed empirical studies are necessary, however, to establish the efficacy of NSOMEs for specific clinical population and treatment targets.

Kinetic comparison of free weight and machine power cleans.

The purpose of this investigation was to compare the kinetic characteristics of the power clean exercise using either free weight or machine resistance. After familiarization, 14 resistance trained men (mean +/- SD; age = 24.9 +/- 6.2 years) participated in two testing sessions. During the initial testing session, one-repetition maximum performance (1RM) was assessed in either the free weight or machine power clean from the midthigh. This was followed by kinetic assessment of either the free weight or the machine power clean at 85% of 1RM. One week after the initial testing session, 1RM performance, as well as the subsequent kinetic evaluation, were performed for the alternate exercise modality. All performance measures were obtained using a computer-interfaced FiTROdyne dynamometer (Fitronic; Bratislava, Slovakia). Maximum strength (1RM) and average power were significantly greater for the free weight condition, whereas peak velocity and average velocity were greater for the machine condition (p < 0.05). Although peak power was not different between modalities, force at peak power (free weights = 1445 +/- 266 N, machine = 1231 +/- 194 N) and velocity at peak power (free weights = 1.77 +/- 0.28 m x s(-1), machine = 2.20 +/- 0.24 m x s(-1)) were different (p < 0.05). It seems that mechanical limitations of the machine modality (i.e., lift trajectory) result in different load capacities that produce different kinetic characteristics for these two lifting modalities.

Babbling, chewing, and sucking: oromandibular coordination at 9 months.

PURPOSE: The ontogeny of mandibular control is important for understanding the general neurophysiologic development for speech and alimentary behaviors. Prior investigations suggest that mandibular control is organized distinctively across speech and nonspeech tasks in 15-month-olds and adults and that, with development, these extant forms of motor control primarily undergo refinement and rescaling. The present investigation was designed to evaluate whether these coordinative infrastructures for alimentary behaviors and speech are evident during the earliest period of their co-occurrence. METHOD: Electromyographic (EMG) signals were obtained from the mandibular muscle groups of 15 typically developing 9-month-old children during sucking, chewing, and speech. RESULTS: Unlike prior investigations of 12- and 15-month-olds and adults, 9-month-olds' analyses of peak correlations among agonist and antagonist comparisons of mandibular EMG data revealed weak coupling during sucking, chewing, and babble; associated lag values for antagonist muscle groups indicated greater synchrony during alimentary behaviors and less synchrony during babble. Unlike the speech data of 15-month-olds, 9-month-olds exhibited consistent results across speech subtasks. CONCLUSION: These findings were consistent with previous results in which mandibular coordination across behaviors was more variable for younger age groups, whereas the essential organization of each behavior closely reflected that seen in older infants and adults.

The influence of myosin heavy chain isoform composition and training status on the patterns of responses for mechanomyographic amplitude versus isometric torque.

The purpose of this study was to examine the influence of myosin heavy chain (MHC) isoform composition and training status on the mechanomyographic (MMG) amplitude versus isometric torque relationship for the vastus lateralis. Five resistance-trained (mean +/- SD age = 23.2 +/- 3.7 years), 5 aerobically trained (mean +/- SD age = 32.6 +/- 5.2 years), and 5 sedentary (mean +/- SD age = 23.4 +/- 4.1 years) men performed isometric muscle actions of the leg extensors in 20% increments from 20% to 100% of the maximum voluntary contraction. Biopsies from the vastus lateralis revealed that the MHC composition for the resistance-trained subjects was 59.0 +/- 4.2% Type IIa, 0.1 +/- 0.1% Type IIx, and 40.9 +/- 4.3% Type I. The aerobically-trained subjects had 27.4 +/- 7.8% Type IIa, 0.0 +/- 0.0% Type IIx, and 72.6 +/- 7.8% Type I MHC. The sedentary subjects had 42.1 +/- 7.8% Type IIa, 17.8 +/- 6.4% Type IIx, and 40.1 +/- 10.9% Type I MHC. There were no consistent patterns of responses for the resistance-trained, aerobically trained, or sedentary subjects for MMG amplitude versus torque. Thus, differences in MHC isoform composition and training status did not explain the unique torque-related patterns for MMG amplitude.

Comparison of mid-term clinical outcomes after primary total hip arthroplasty with Oxinium vs cobalt chrome femoral heads.

The purpose of this investigation was to assess the midterm clinical outcomes after implantation of Oxinium (OX) vs cobalt-chrome (CC) femoral heads. Primary total hip arthroplasty (THA) procedures were performed in 100 patients. After randomization, half of the patients received OX femoral heads and half received CC femoral heads. At a minimum follow-up of 2-years, stem survival was 98% for both groups. The mean Harris Hip score was 92 for OX and 92.5 for CC, with mean WOMAC scores of 84.9 and 87, respectively. For SF-12, the OX group had mean physical and mental component scores of 45.2 and 53.8 and the CC group 49.2 and 52.6, respectively. At a minimum follow-up of 2 years, clinical outcomes for THA procedures using OX and CC femoral heads appear equivalent.