Muscular Recruitment Research Articles

Strategies for improving the pedaling technique.

Pedaling technique which can be defined as the way the cyclists pedal, has been mostly studied in lab conditions from pedal force kinetic, joints kinematic, and/or muscular activity patterns because it is considered as a main factor for gross efficiency (GE). Although this method is much controversial, its quality has extensively been evaluated from the index of pedal force effectiveness (IFE), i.e. the ratio between the effective to the total pedal force. Over the last thirty years, preferred pedaling technique has been compared between the experienced cyclists and non-cyclists and also often been manipulated by instructing these subjects to improve their effective force production during the downstroke phase ("pushing"), the upstroke phase ("pulling-up") or around top and bottom dead centers ("circling"). It has been shown that PREF pedaling technique is much repeatable across crank cycles in experienced cyclists than in novice cyclists. PULL involves a significant increase of IFE compared to PREF, mainly attributed to the increase of the muscular work of hip (RF) and knee flexors muscles (BF) during the upstroke. This improvement is larger in non-cyclists than in experienced cyclists but it can be optimized in the latter after a short-term training (2-4 weeks) with pedal force feedback or uncoupled cranks. Despite that PULL enhances a lower muscular recruitment of contralateral knee extensors, GE and cycling performance variables are not significantly increased, probably due to the reversal effect of training with normal cranks and the highly robust pedaling technique of experienced cyclists. The question arises, as to whether or not, changes in pedaling technique can improve cycling efficiency if enough time is given for cyclists to adapt to a new pedaling technique. Further studies should investigate the pedaling techniques in more "ecological" conditions, as there is not probably one but several pedaling techniques that could optimize cycling efficiency according to the pedaling conditions (time-trial, uphill, road, off-road and track cycling), and should also focus on the potential effects of long-term training of PULL pedaling technique on cycling efficiency and cycling performance.

Knee Forces During Landing in Men and Women.

Sex differences in biomechanics may provide one explanation for the greater incidence of knee injuries in women, but few studies have compared internal forces. In this study, a musculoskeletal model was used to compare male and female, bilateral and unilateral landings based on motion capture and force plate data. Participants were classified as landing medially or laterally loaded based upon the mediolateral load share at the knee (bilateral: p < 0.001, η2=0.452; unilateral: p < 0.001, η2 = 0.444). Knee kinematics and ground reaction forces were not different between the two groups (p > 0.05, η2 = 0.001 – 0.059), but there were differences in muscular recruitment. Landing strategy did not appear to be dependent on sex. However, for both medially and laterally loaded bilateral landings men had greater gluteal (p = 0.017, η2 = 0.085) and hamstrings forces (p < 0.001, η2 = 0.183), whereas women had greater quadriceps forces (p = 0.004, η2 = 0.116). This study demonstrates an association between muscular recruitment and medially loaded landings. Landing strategy seems to be a function of skill not sex; however, within a particular landing strategy there may be sex differences in muscular activation that contribute to the difference in injury rates.

A Deep Learning Approach to EMG-Based Classification of Gait Phases during Level Ground Walking

Correctly identifying gait phases is a prerequisite to achieve a spatial/temporal characterization of muscular recruitment during walking. Recent approaches have addressed this issue by applying machine learning techniques to treadmill-walking data. We propose a deep learning approach for surface electromyographic (sEMG)-based classification of stance/swing phases and prediction of the foot–floor-contact signal in more natural walking conditions (similar to everyday walking ones), overcoming constraints of a controlled environment, such as treadmill walking. To this aim, sEMG signals were acquired from eight lower-limb muscles in about 10.000 strides from 23 healthy adults during level ground walking, following an eight-shaped path including natural deceleration, reversing, curve, and acceleration. By means of an extensive evaluation, we show that using a multi layer perceptron to learn hidden features provides state of the art performances while avoiding features engineering. Results, indeed, showed an average classification accuracy of 94.9 for learned subjects and 93.4 for unlearned ones, while mean absolute difference ( ± S D ) between phase transitions timing predictions and footswitch data was 21.6 ms and 38.1 ms for heel-strike and toe off, respectively. The suitable performance achieved by the proposed method suggests that it could be successfully used to automatically classify gait phases and predict foot–floor-contact signal from sEMG signals during level ground walking.

Vibration as an adjunct to exercise: its impact on shoulder muscle activation.

There is an interest within elite sport in understanding the impact of a vibrating platform as an adjunct to exercise in the training and rehabilitation of throwing athletes. However, there has been no comprehensive evaluation of its impact on the rotator cuff muscles or its effect on the timing of shoulder muscle recruitment more globally. Twenty healthy participants were recruited with EMG recorded from 15 shoulder girdle muscles. Isometric shoulder flexion at 25% maximal voluntary contraction was performed in three testing scenarios [no vibration; whole body vibration (WBV); and arm vibration (AV)]. A press up and triceps dips with and without vibration were also performed. Muscular recruitment was assessed pre- and post-vibration exposure as participants initiated forward flexion. Activation of the anterior deltoid (p = 0.002), serratus anterior (p = 0.004), and rotator cuff muscles (p = 0.004-0.022) occurred significantly earlier following exposure to vibration. Significantly greater activation was seen in the anterior, middle and posterior deltoid, upper, middle and lower trapezius, serratus anterior, teres major, latissimus dorsi, supraspinatus, and infraspinatus when the isometric contraction was performed with either WBV and/or AV (p = < 0.001-0.040). Similarly, increased activation was also demonstrated during the press up and triceps dips when performed with vibration. The use of vibration as an adjunct to exercise provokes a near global increase in shoulder muscle activation level. Furthermore, exposure to vibration alters muscular recruitment improving readiness for movement. This has potential implications within elite sport for both training and game preparation; however, further longitudinal work is required.

Neuromotor control during stair ambulation in individuals with patellofemoral osteoarthritis compared to asymptomatic controls

BackgroundPatellofemoral OA is characterized by PF pain during activities that load a flexed knee. Stair stepping ability is frequently impaired, yet little is known of the muscular recruitment strategies utilized during this task. Altered recruitment strategies may provide targets for clinical interventions. We aimed to determine if people with PFOA ascend and descend stairs with different muscular recruitment strategies compared to similar aged healthy individuals. MethodsTwenty-two people with PFOA and 20 controls were recruited. Electromyographic recordings from gluteus maximus and medius, medial and lateral hamstrings, vastus medialis and lateralis, medial and lateral gastrocnemius and soleus were acquired during stair ascent and descent. Force plate data was acquired to determine timing of foot placements and characterize dynamic stability. ResultsSeventeen people with PFOA (59 ± 10 years, 73 ± 13 kg, 167 ± 9 cm) and 15 controls (57 ± 10 years, 73 ± 16 kg, 171 ± 11 cm) had complete data. People with PFOA demonstrated: longer vastii activation duration during descent (lateralis: p = 0.01; medialis: p = 0.02); earlier onset of vastus lateralis for ascent (p < 0.01) and descent (p = 0.04); earlier onset of soleus in descent (p = 0.04); and shorter duration of GMax during ascent (p = 0.05). Peak Fz timing (time between the start of the anticipatory postural adjustment and the end of the stepping task) was ∼70ms later during stair descent in PFOA compared to controls (p = 0.01). SignificancePeople with PFOA utilize muscular activation strategies consistent with minimizing knee pain during stair ambulation. Clinical interventions aimed at gluteal and quadriceps activation may be warranted in PFOA.

Muscular recruitment is associated with muscular function and swelling following eccentric contractions of human elbow flexors.

This study investigated the relationship between muscle fiber recruitment and the magnitude of muscle damage by isotonic eccentric contractions (ECCs). Ten healthy men (age: 27.2±6.0 y, height: 174. 0±5.3 cm, body mass 70.1±2.1 kg) were recruited in this study. Subjects performed 30 ECCs of the elbow flexors using a dumbbell adjusted to 40% and 80% one repetition maximum of each individual. The dependent variables maximal voluntary isometric contraction (MVC) torque, Range of Motion (ROM), delayed onset muscle soreness (DOMS), cross-sectional area (CSA) and transverse relaxation time (T2) of magnetic resonance imaging (MRI) were measured immediately before, immediately after and 1, 3, and 5 days after each exercise. The decreased MVC and limited ROM were significantly greater for 80% than that 40% (P<0.05) at immediately after ECCs. However, no significant difference between 40% and 80% was found for DOMS. CSA at 5 days after ECCs was significantly higher 80% (P<0.05) than 40% (P<0.05). No significant changes in post T2 (acute T2) was found for 40%, but an increased acute T2 was observed in 80% (P<0.05). We found a significant correlation between the change in T2 at immediately after and MVC at immediately after (r=0.77, P<0.05). In addition, a significant correlation between the change in T2 at immediately after and change in CSA at 3 days after (r=-0.83, P<0.05) was found. We conclude that the muscle strength loss and swelling following ECCs are related to the muscle fiber recruitment.

Pre-exhaustion Exercise Differentially Influences Neuromuscular Fatigue Based on Habitual Physical Activity History.

Harlan, KG, Merucci, RB, Weaver, JJ, Windle, TC, and Malek, MH. Pre-exhaustion exercise differentially influences neuromuscular fatigue based on habitual physical activity history. J Strength Cond Res 35(3): 739-745, 2021-Although there is anecdotal evidence of a potential physiological benefit of pre-exhaustion exercise to enhance muscular recruitment, few studies have systematically examined the effect on neuromuscular activity. Moreover, a subject's habitual physical activity history may, in part, contribute to the muscle's response on a subsequent workbout after a single pre-exhaustion workbout. To date, no studies have examined the effect of pre-exhaustion exercise on the electromyographic fatigue threshold (EMGFT). The purpose of this study, therefore, is to determine whether pre-exhaustion exercise influences the EMGFT. Specifically, we were interested in determining whether or not there is a dichotomous response to pre-exhaustion exercise based on the individual's habitual physical activity history. Thus, we hypothesized that healthy active subjects would have reduced EMGFT values, whereas elite runners would have increased EMGFT values as a result of the pre-exhaustion exercise. Eight healthy college-aged men (mean ± SEM, age = 24.5 ± 0.3 years; body mass = 83.1 ± 3.0 kg; and height = 1.80 ± 0.02 m) and 9 elite runners (mean ± SEM, age = 23.4 ± 0.7 years; body mass = 70.3 ± 2.7 kg; and height = 1.79 ± 0.03 m) participated in current study. Each subject visited the laboratory on 2 occasions separated by 7 days and performed the single-leg knee-extensor ergometry test. For one of the visits, the subjects performed the Thorstensson test (50 continuous, concentric knee extensions) before the single-leg knee-extensor ergometry. The EMGFT was measured on both visits for all subjects. For healthy subjects, we found that the EMGFT was significantly reduced after performing the 50 isokinetic knee extensions (control: 27 ± 6 W vs. Thorstensson: 21 ± 6.0 W; p = 0.001), whereas for elite runners, there was no significant mean differences between the 2 visits (control: 38 ± 3 W vs. Thorstensson: 39 ± 2 W; p = 0.813). These results suggest that 50 repetition of isokinetic muscle action, as a method of pre-exhausting the quadriceps femoris muscles, may be influenced by the subject's habitual exercise history.

Friday, September 28, 2018 4:05 PM–5:05 PM abstracts: cervical myelopathy and deformity: 255. Neuromuscular activity during gait in patients with cervical spondylotic myelopathy

BACKGROUND CONTEXT Gait impairment is a hallmark of cervical spondylotic myelopathy (CSM) and has been shown to affect quality of life. Some studies describe the gait as spastic, while others suggest a paretic component. Further electromyographic (EMG) characterization of the gait cycle may help elucidate the true neuromuscular pathology with implications on prognosis and rehabilitation techniques. PURPOSE To compareneuromuscular activity in CSM patients to healthy, age-matched controls. STUDY DESIGN/SETTING Nonrandomized, prospective, concurrent control cohort study. PATIENT SAMPLE Forty patients with symptomatic CSM prior to any surgical intervention and 25 healthy controls. OUTCOME MEASURES Integrated electromyography (iEMG), peak EMG, time to peak EMG, mean power frequency and time of muscle onset. METHODS Forty patients with symptomatic CSM prior to any surgical intervention and 25 healthy controls had neuromuscular activity measured during a series of over-ground gait trials at a self-selected speed. External Oblique (EO), Multifidus (Mf), Erector Spinae (ES), Rectus Femoris (RF), Semitendinosus (ST), Tibialis Anterior (TA), Medial Gastrocnemius (MG) and Medial Deltoid (MD) were assessed. Differences in integrated electromyography (iEMG), peak EMG, time to peak EMG, mean power frequency and time of muscle onset were assessed using one-way ANOVA. RESULTS Compared to controls, patients with CSM demonstrated significantly less activation amplitude of the EO (0.72±0.79 vs. 1.52±2.05mV; p=.034), ST (3.02±5.37 vs. 5.86±9.19mV; p=.05), and MD (0.876±0.81 vs. 2.6±3.77mV; p=.008). They demonstrated significantly higher peak EMG muscle activity in the MD (0.06±0.044 vs. 0.03±0.021mV; p=.031) and significantly longer time to peak EMG muscle activity in the Mf (20.2±8.5 vs. 16.8±8.9ms, p=0.050), ES (18.2±6.7 vs. 8.9±7.2ms; p CONCLUSIONS Patients with CSM often present with a gait disturbance that has significant implications on quality of life. This study's findings demonstrate difficulty with muscular recruitment in lower extremity stabilizing musculature, coupled with increased peak EMG activity in the MD, representing compensatory mechanisms in the upper extremities, as well. This study contributes to existing knowledge on EMG muscle activity in patients with untreated CSM and will be useful in future studies investigating neuromuscular function in patients with CSM after surgical decompression.

An interactive tool for the analysis of muscular recruitment during walking task

The present work proposes an interactive software tool for surface electromyography signal processing and analysis, focused on the assessment of muscular activations during walking and easy-to-use also for users without signal treatment knowledge. The tool is based on two logical steps: first, an automatic detection of muscle activations is provided; then, the user can tune the value of each processing parameter, with a real-time visual feedback. A stride-to-stride evaluation of muscular recruitment and a co-contraction recognition are available, together with the computation of an average myoelectric activation pattern. The tunable signal processing tailors the analysis to any considered application, allowing to extract information from low-quality signals. A muscle activity characterisation from the single stride to the whole walking trial is also provided. Beyond gait analysis and muscles activation timing identification, this tool could be valuable also in an educational scenario, considering the interactive characteristics of the graphical user interface.

A comparative study on the recruitment of shoulder stabilizing muscles and types of exercises.

The shoulder is susceptible to disturbances caused by microtraumas due to direct contact of the surrounding skeletal structures or failure of the soft parts of the rotator cuff and other muscles inserted into the glenohumeral joint. The purpose of the study was to compare the electromyographic signal in the stabilizing muscles of the shoulder during the diagonal elevation exercise as recommended by the proprioceptive neuromuscular facilitation (PNF) method and dumbbell exercise. This study is classified as Quase-experiment. Subjects were instructed to perform diagonal standard exercises and the electromyographic signal was detected from pectoralis muscles, middle and upper trapezius of dominant limb in each subject. We observed greater muscular recruitment when the PNF method was adopted in comparison with the dumbbell workouts for the trapezius upper and middle fiber muscles and for the major pectoralis (267,30 μv/181,02 μv; 235,76 μv/;164,47 μv; 299,87 μv/148,69 μv; P<0.001). The PNF method promotes a greater recruitment of the shoulder dynamic stabilizing muscles during diagonal elevation exercises. Being so, such kinesiotherapeutic technique may be effectively used in the prevention, treatment and rehabilitation of shoulder disorders.

Impact of Stability Ball Sitting during Semi-recumbent Exercise

Purpose: This study determined if sitting on a stability ball (B), when compared to sitting on a chair (C), affects cardiorespiratory and muscular recruitment during semi-recumbent exercise. Methods: Participants sat on B or C behind a cycle ergometer using the bike seat for hand griping. Open-circuit spirometry and HR were monitored continuously during graded exercise. Initial two stages of exercise also had hip movements and the right arm, trunk, and leg EMGs recorded. Eighteen apparently healthy adults exercised twice, one trial on B and the other trial on C (order randomized). ANOVA for repeated measures (α < 0.05) was used for statistical analysis. Results: Only at peak was VO2 significantly higher (P = 0.001) for B compared to C. There was no significant (P = 0.291) difference between B and C for HR. Stage 2 hip movements were significantly (P < 0.001) higher while some leg EMGs were significantly (P < 0.019) lower on B compared to C. In addition, flexor digitorum EMG was significantly (P < 0.036) higher on B compared to C. Conclusion: The stability ball increases hip motion and may alter muscular recruitment pattern during semi-recumbent exercise with little impact on cardiorespiratory parameters.

Kinematic and electromyographic analysis of school children gait with and without load in the backpack

AbstractIntroduction: Excessive load on the backpacks can lead to musculoskeletal injuries and gait alterations. The objective of this study was to analyze the electromyographic (EMG) activity in association to the kinematic during the stance and balance phases of gait performed with and without the use of the backpack. Methods Twelve volunteers have executed a gait cycle in 3 tasks: without the school backpack (SM), with a backpack with load equivalent to 10% (M10) and 20% (M20) of the body weight (BW). It was evaluated the ankle, knee and hip angular excursion (AE), linear displacement (LD) of the toe and ankle, knee, hip, shoulder, head and EMG activity of the tibialis anterior (TA), vastus medialis (VM), rectus abdominis (RA), gastrocnemius lateral (GL), biceps femoris (BF) and spinal erector (EE) muscles. Results In the LD in the stance phase there was an AP increase for the toe and ankle, hip and head (p<0.043). In the balance phase for VT (vertical) direction, the shoulder presented a smaller displacement as well as the toe, ankle, knee, hip, shoulder and head in the ML direction. In the AP direction, the toe displacement was smaller as well as the ankle (p < 0.038). The AE in both phases was smaller for the hip (p <0.006). In the balance phase the IEMG was higher for the RA (p = 0.034). Conclusion These results suggest that the transport of school backpacks with loads of more than 10%BW causes changes in the kinematic and in the muscular recruitment pattern.

FES Bike Race preparation to Cybathlon 2016 by EMA team: a short case report.

FES-assisted cycling has been recommended to people struggling to emerge from a disability to more functioning life after spinal cord injury. Recommendations issued by a gowing number of scientific papershas promised toimprove body composition and physical activity levels, as well as to controlinvoluntary muscle response; favoring activity and participation which break new grounds in expanding locomotion, leisure and occupational options for people with paraplegia and tetraplegia. In this report we described our experience to select and prepare a pilot to compete in the FES Bike Race modality at Cybathlon 2016 in Kloten (Zurick). He was a man, 38 years old, with a complete spinal cord injury, level T9, three years of injury. He took part in a two preparation phases lasting respectively 18 and 12 weeks each: (1st) pre-FES-cycling and a (2nd) FES-cycling. The 1st phase aimed to explore electrical stimulation response in the quadricps, hamstrings and gluteus muscles; searching for a standard muscular recruitment enable to propel the pedals of a trike. Following, in the 2nd phase, stationary to mobile FES-cycling was performed at the same time the development of the automation and control systems were being incorporated in the trike. We adapted a commercial tadpole trycicle anda pilot controlled system. Although we had planned a three session by week protocol, for reasons of term and time to finish the trike development and be prepared to compete, in the last two weeks before the Cybatlhon an intense level of exercise was maintained. After the race, we noticedinflammatory signs on the left knee which later revealed a patella fracture. The video footage analysis confirmed ithappened during the race’s first lap.

Effects of trapezius kinesio taping on scapular kinematics and associated muscular activation in subjects with scapular dyskinesis

Study DesignCrossover repeated-measure design. IntroductionScapular dyskinesis rehabilitation programs that focus on inhibiting upper trapezius (UT) and activating the lower trapezius (LT) may assist in restoring scapular movements. We hypothesized that taping may be able to normalize scapular movements and associated muscular recruitment. Purpose of the StudyThe purpose of this study was to investigate the immediate effects of kinesio taping over trapezius on scapular kinematics and muscular activation in different dyskinesis patterns. We expected that taping can improve scapular kinematics and muscular activation in subjects with dyskinesis. MethodsFifty-four participants with inferior angle prominence (pattern I), medial border prominence (pattern II), and mixed pattern (pattern I + II) were recruited. Kinesio taping was applied over 3 parts of trapezius muscles, including UT, middle trapezius (MT), and LT. The scapular kinematics and electromyographic data of trapezius and serratus anterior were collected during scapular plane elevation without taping and after each taping application. ResultsUT taping decreased UT activity (5%-7%; P = .001-.003) in 72% of participants with pattern II and pattern I + II dyskinesis, with increased posterior tipping (2.2°-2.5°; P = .003) in pattern II dyskinesis. MT taping increased UT activity (3%; P = .003) in 48% of participants with pattern II dyskinesis. DiscussionThe taping over the trapezius muscle may help to restore coordinated scapular muscle balance and increased upward rotation of the scapula, especially in pattern II dyskinesis. Although no electromyography or kinematic difference was found with LT taping in each dyskinesis pattern, methods of applying LT taping need to be further investigated. ConclusionReduced UT muscle activity and scapular posterior tipping are appropriate when applying taping over UT muscle in patterns II and I + II dyskinesis. Caution should be taken when applying taping over MT and LT muscles in terms of increased UT activity, especially in pattern II dyskinesis.

Co-contraction activity of ankle muscles during walking: A gender comparison

The study aimed to assess possible differences between healthy, young males and females in co-contraction activity of tibialis anterior and gastrocnemius lateralis during gait at self-selected speed and cadence. The Statistical-Gait-Analysis methodology, allowing a statistical characterization of gait by averaging spatial-temporal and sEMG-based parameters over hundreds of strides per walking trial, was applied on thirty age-matched subjects: 15 males and 15 females. Co-contractions were assessed as the overlapping periods between muscular activities. Results showed the occurrence of four different co-contractions during gait cycle, for both groups. No significant differences in activation instants (ON-OFF) were detected between groups. Otherwise, all the co-contractions occurred in higher number of strides (%) in females, respect to males: in early stance (40.7 ± 18.7% vs. 18.9 ± 11.0%, p < 0.001), mid-stance (41.5 ± 15.2% vs. 26.0 ± 22.8%, p < 0.005), pre-swing (16.6 ± 7.3% vs. 7.1 ± 4.7%, p < 0.001), and swing (79.4 ± 13.7% vs. 55.6 ± 19.3%, p < 0.001). This overall higher occurrence of ankle-muscle co-contractions, associated to a more complex muscular recruitment, seems to reflect a female need for a higher level of ankle-joint stabilization. Thus, present findings indicated gender as a not negligible factor in the interpretation of muscular co-contraction variability during walking and suggested the suitability of gender-based approaches in clinical studies and in developing reference frameworks.

Efeitos agudos da utilização de dispositivos geradores de instabilidade externa sobre o desempenho neuromuscular

DOI: http://dx.doi.org/10.5007/1980-0037.2016v18n6p722 Physical training with the use of instability generator devices has become popular in the health area, in sport training and clinical practice (mainly in the prevention and treatment of injuries). To understand how the process of using these devices occurs and the results of their acute effects is important to guide professionals in choosing the appropriate device. The aim of this review was to present the main features of instability devices and analyze their acute effects on core muscle activation, neuromuscular performance and activation of lower and upper limbs. Studies have shown that the main acute effects of exercises performed with these devices are: 1) increased activation / muscular recruitment (especially in the middle zone or core); 2) greater co-activation of antagonist muscles (trunk, upper and lower limbs), with increased stiffness and joint stability; 3) lower force output, power and speed in extremities.

Assessing the effect of manual physical activity on proximal hand phalanges using Hellenistic and modern skeletal samples from Greece

In humans, physical activity is an important regulator of bone size. Furthermore, hand bones have been proposed as a potential avenue for assessing patterns of manual activity. However, there are very few studies presenting a metric comparison of proximal hand phalanges among different populations. Moreover, an osteoarchaeological approach to the manual activities performed by an ancient population is yet to be made. In this framework, this study aims at assessing and interpreting the metric variation in these bones between a documented modern Greek sample (20th century) and a Hellenistic sample from Demetrias (3rd–1st century BCE), in terms of size and sexual dimorphism. Ancient males were significantly larger than females for ten phalangeal measurements out of 35. Even though the degree of sexual dimorphism was lower in the Hellenistic material (the maximum sexual dimorphism observed – 12.46%) than in modern sample (the maximum observed – 21.19%), the ranking of rays and bone parts by sexual dimorphism was similar in both populations. No metric difference was observed between modern and ancient males, whereas ancient females were larger than modern females in seven dimensions (the maximum variation observed was 11.58%), which involved the bases and midshafts of phalanges. Given that these dimensions are affected by the degree of muscular recruitment for the formation of various hand grips, it is suggested that ancient females were involved in manual activities of greater grasping variance than modern females. Indeed, the historical and archaeological sources suggest that sexual distribution of labour in the Hellenistic society seems to explain the differences estimated between the sexes and the two populations under study.

Limb and back muscle activity adaptations to tripedal locomotion in dogs.

Alterations in muscle recruitment are key to the functional plasticity of the mammalian locomotor system. One particularly challenging situation quadrupeds may face is when the functionality of a limb is reduced or lost. To better understand how mammals manage in such situations and which muscular adaptations they exhibit when locomoting on three legs, we recorded the activity patterns of two limb and one back extensor muscle in nine dogs using surface electromyography. We compared the timing and the level of recruitment before and after the loss of a hindlimb was simulated. Both the intensity and the timing of the activity changed significantly in the m. vastus lateralis of the remaining hindlimb, consistent with this limb bearing a greater proportion of the body weight as well as with previously reported kinematic changes. In accordance with the greater body weight supported by the forelimbs, the m. triceps brachii showed first and foremost an increased level of excitation. The very asymmetrical changes in the timing and the level of activity in the m. longissimus dorsi reflects the highly asymmetrical functional requirements imposed on the trunk and the pelvis when one hindlimb is no longer involved in the production of locomotor work while the other hindlimb partially compensates the loss. Integration of our electromyographical findings with kinetic and kinematic results illustrates that dogs exhibited a well-coordinated response to the functional requirements of tripedalism and underlines the importance of moment-to-moment modulation in muscular recruitment for the functional plasticity of the mammalian locomotor system.

A 3-D Stability-Based Dynamic Computational Model of Human Trunk Movement: Towards the Development of a Paradigm for Forensic Spinal Injury Biomechanical Analysis

Background: Spinal injuries and associated litigation continue to pose significant human and economic challenges globally. Biomechanical predictive simulation models of the spine provide time and cost effective tools for forensic injury biomechanical quantitative analysis.Methods: A 3-D computational model that includes 18 muscles was developed to simulate the motion of the human trunk. Three physiologically based performance indices were used to model the optimal trajectories associated with trunk movement. The moment generated around the lumbosacral joint was computed using inverse dynamics. The contribution of muscles to the moment was evaluated by performing static stability-based optimization, where trunk movement from an upright position to 60 degrees of flexion was simulated. Contribution of the intrinsic mechanism to spinal stability was addressed by adding stability constraints to the optimization routine while allowing for an increase in the activity of the antagonistic muscles.Results: Co-contraction of agonistic and antagonistic muscles in the resulting computational model increases joint stiffness around the L5/S1 joint. Muscle spindles provide reflexive feedback to control the trunk position during the execution of the optimal trajectory. Increasing the time delay in the reflex mechanism reduces spinal stability.Conclusion: The main contribution of this work is two-fold: 1. The novel use of three physiologically plausible indices of performance to simulate spinal motion with and without stability constraints, and 2. The incorporation of several well established feed forward and feedback controls in the model. The indices of trunk performance resulted in different motion patterns and muscular recruitment patterns. The model predicted that imposing trunk stability causes higher spinal stiffness by increasing muscular recruitment in alignment with experimental data. This study provides a computational framework for modeling and predicting spinal movement that can be used towards quantitative forensic spinal injury biomechanical analysis.

Muscular fatigue of the lower limb and subsequent joint angle adaptations during a 16.1km cycling time trial

Background: Effective muscular recruitment during cycling is crucial to optimising performance.  As such, much research has examined when muscles are active during the pedal revolution and how muscle co-activation may influence pedalling technique but little evidence associated with the effect of fatigue on lower limb joint angles and its subsequent effect on power output and muscle recruitment.  Purpose: Are changes in muscular recruitment patterns and changes in lower limb kinematics detrimental to performance?  Methods: A preliminary case study of a well-trained veteran cyclist (V I‡O2peak  49.9 ml . kg-1 . min-1 and PPO of 400W) conducted a 16.1km simulated cycling time trial on a Wattbike Pro at 80% PPO with a cadence of 98 rpm.  Bilateral surface EMG were employed using pairs of Ag/AgCl electrodes adhered to both right and left vastus medialis (VM), biceps femoris (BF), tibialis anterior (TA) and gastrocnemius (GM).  Intervals of sixty seconds in duration, of 3D kinematic and electromyography (EMG) data were synchronised using a Vicon motion capture system throughout the time trial.  Ten consecutive pedal revolutions per 60 s interval were processed for subsequent analysis.    Kinematic and EMG data signals were imported into Visual 3D v.5 and Matlab for processing.  Results: There were statistically significant changes (p<0.05) in all kinematic data across nine time points.  Fundamental changes occurred between minute 10-12 with a decrease in flexion angle for the left hip (z = -9.56, p<0.05, r = 0.55), and the right hip, (z = -7.67, p<0.05, r = 0.44).  The left ankle starts to have a greater planter flexion (z = -9.69, p<0.05, r = 0.56) between minutes 10-12 and this continues to have a significant change between time points for the remainder of the trial.  The magnitude of EMG data revealed that there were statistically significant changes (p<0.05) in all muscles across seven time points.  Decreases in the magnitude of activation were observed between minutes 8-10 for both the left (z = -9.17, p<0.05, r = 0.53) and right (z = -8.21, p<0.0005, r = 0.48) TA.  The frequency domain EMG analysis indicated a trend towards lower frequencies being recorded for the left and right TA and GM with a trend towards higher frequencies being recorded for the left and right VM.  Analysis of the Wattbike data indicated that there were statistically significant differences from minutes 1 to 20 between left and right angle to peak force applied to the crank (t(19) = 20.89, p<0.05) with no statistical significance between left and right limb percentage use (95% CI 2.81, 3.31%).  Indications showed that there was a higher magnitude of activation for the left leg across all muscles tested and the Wattbike data indicates greater power generation on the left side of the pedal revolution.  Discussion: Based on the results from this study there were decreases in the ankles range of motion (ROM) with increases in hip flexion from minute 10-12 with changes in neuromuscular activity between minutes 8-10 then there were smaller effect changes for the remainder of the time trial.  The alterations in the EMG median frequency indicated a trend towards muscular fatigue for TA and GM with increases in neuromuscular activity in both VM’s possibly counteracting fatigue.  The ankle’s decrease in ROM may be a product of fatigue associated with the TA and GM but by becoming stiffer it may optimise the foot/pedal interface.  Even with these changes in kinematic and EMG data the power output remained constant.  Conclusion: As this was a case study further work in this area needs to be considered in establishing variability in joint angles and how they may be beneficial/detrimental in generating the same level of power output when fatigued.  An association of muscular fatigue in cycling and changes to lower limb joint angle variability requires further investigation examining joint coupling patterns, independent pedal power analysis and cross reference to physiological parameters for fatigue to establish strategies that may be beneficial in improving cycling performance.