Evolutionary accounts of empathy often focus on the ways in which empathy-motivated helping can give rise to indirect fitness benefits. These accounts posit that empathy is adaptive insofar as it motivates strategic helping behavior, but they neglect a key feature of the empathic process – it can prepare one to act effectively within a shared environment. In particular, adopting the affective and motivational states of others provides a rapid and automatic way to avoid danger and threat, which play a disproportionately large role in shaping behavior. Based on the idea that empathic processes facilitate adaptive reactions to threat, I conducted four experiments to test the hypothesis that empathic reactions reflect withdrawal motivation. In the first experiment I used electroencephalography (EEG) to measure baseline right-frontal cortical asymmetry, a reliable neural correlate of withdrawal motivation. I then assessed empathic reactions to images of children ostensibly taken from a charity campaign. Participants who showed greater right-frontal cortical asymmetry also showed stronger empathic reactions to the images. In the second study I used self-report measures fear and anger to assess dispositional withdrawal- and approach-motivation, respectively. This time, participants indicated their empathic reactions to targets experiencing happiness and targets experiencing sadness. Empathy for both types of targets was positively related to fear and negatively related to physical aggression, again supporting a link between empathy and withdrawal motivation. In the third study I measured state withdrawal motivation by using facial electromyography (EMG) to assess disgust expressions towards charity images. These expressions were positively correlated with empathic reactions, demonstrating that state withdrawal motivation is also positively related to empathy. In the final study I manipulated approach and withdrawal emotions by having participants make emotional facial expressions. Focusing on fear and anger, I found that participants were more empathic when making fearful faces than when making angry faces, although these results must be interpreted with caution, as the manipulation may not have had the intended effects on emotional state. Taken together, these four studies provide converging evidence of an association between withdrawal motivation and empathy, supporting the idea that empathy plays a role in the adaptive response to threat.

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Purpose: Biomechanical differences between people with low back pain (LBP) and healthy controls have been shown previously. LBP has been associated with standing postures in occupational settings. A transient pain-generating model allows for comparisons between pain developers (PD) and non-pain developers (NPD). The first objective was to utilize a multifactorial approach to characterize differences between PD and NPD individuals. The second objective was to investigate the impact of exercise on LBP during standing. Methods: Forty-three participants without any history of LBP volunteered for this study. Participants performed pre- and post-standing functional movements and 2-hours of standing. Continuous electromyography (EMG) data were collected from 16 trunk and hip muscles, kinematic and kinetic data were used to construct an 8-segment rigid link model. Vertebral joint rotation stiffness (VJRS) measures were calculated. Participants completed visual analog scales (VAS) rating LBP every 15 minutes during the 2-hr standing. Participants were classified as PD or NPD based on greater than 10 mm increase in VAS. Participants were assigned to exercise (EX) or control (CON) groups. All participants returned for a second data collection following 4-weeks. Results: Forty percent of participants developed LBP during standing. The PD group had elevated muscle co-activation prior to reports of pain (p < 0.05). Following standing, there was a decrease in VJRS about the lateral bend axis during unilateral stance. PDEX had decreased VAS scores during the second data collection (p = 0.007) compared with PDCON. Male PDEX had decreased gluteus medius co-activation during standing (p < 0.05). Between-day repeatability for the CON groups was excellent with intraclass correlation coefficients > 0.80 for the majority of the outcome measures. Conclusions: There were clear differences between PD/NPD groups in muscle activation patterns, prior to subjective reports of LBP, supporting the hypothesis that some of the differences observed between these groups may be predisposing rather than adaptive. An exercise intervention resulted in positive changes in the PD group, both in subjective pain scores as well as muscle activation profiles. Elevated muscle co-activation in the first 15-30 minutes of standing may indicate that an individual is at increased risk for LBP during standing.

Purpose: Biomechanical differences between people with low back pain (LBP) and healthy controls have been shown previously. LBP has been associated with standing postures in occupational settings. A transient pain-generating model allows for comparisons between pain developers (PD) and non-pain developers (NPD). The first objective was to utilize a multifactorial approach to characterize differences between PD and NPD individuals. The second objective was to investigate the impact of exercise on LBP during standing. Methods: Forty-three participants without any history of LBP volunteered for this study. Participants performed pre- and post-standing functional movements and 2-hours of standing. Continuous electromyography (EMG) data were collected from 16 trunk and hip muscles, kinematic and kinetic data were used to construct an 8-segment rigid link model. Vertebral joint rotation stiffness (VJRS) measures were calculated. Participants completed visual analog scales (VAS) rating LBP every 15 minutes during the 2-hr standing. Participants were classified as PD or NPD based on greater than 10 mm increase in VAS. Participants were assigned to exercise (EX) or control (CON) groups. All participants returned for a second data collection following 4-weeks. Results: Forty percent of participants developed LBP during standing. The PD group had elevated muscle co-activation prior to reports of pain (p < 0.05). Following standing, there was a decrease in VJRS about the lateral bend axis during unilateral stance. PDEX had decreased VAS scores during the second data collection (p = 0.007) compared with PDCON. Male PDEX had decreased gluteus medius co-activation during standing (p < 0.05). Between-day repeatability for the CON groups was excellent with intraclass correlation coefficients > 0.80 for the majority of the outcome measures. Conclusions: There were clear differences between PD/NPD groups in muscle activation patterns, prior to subjective reports of LBP, supporting the hypothesis that some of the differences observed between these groups may be predisposing rather than adaptive. An exercise intervention resulted in positive changes in the PD group, both in subjective pain scores as well as muscle activation profiles. Elevated muscle co-activation in the first 15-30 minutes of standing may indicate that an individual is at increased risk for LBP during standing.

Neurological and morphological adaptations are responsible for the increases in strength that occur following the completion of resistance exercise training interventions. There are a number of benefits that can occur as a result of completing resistance exercise training interventions, these include: (i) reduced risk of developing metabolic health issues; (ii) decreased risk and incidence of falling; (iii) improved cardiovascular health; (iv) elevated mobility; (v) enhanced athletic performance; and (vi) injury prevention. Traditional resistance exercise (constant load resistance exercise (CL)) involves equally loaded eccentric and concentric phases, performed in an alternating manner. However, eccentric muscle actions have unique physiological characteristics, namely greater force production capacity and lower energy requirements, compared to concentric actions. These characteristics have led to the exploration of eccentric-focused resistance exercise for the purposes of injury prevention, rehabilitation, and enhancement of functional capacity. Accentuated eccentric load resistance exercise (AEL) is one form of eccentric-focused resistance exercise. This type of resistance exercise involves a heavier absolute external eccentric phase load than during the subsequent concentric portion of a repetition. Existing training study interventions comparing AEL to CL have demonstrated enhancements in concentric, eccentric, and isometric strength with AEL. However, no differences in strength adaptations have been reported in other AEL vs. CL training studies. Only 7 d intensified AEL training interventions have measured neuromuscular variables, providing evidence that enhanced neuromuscular adaptations may occur when AEL is compared to CL. Therefore, a lack of information is currently available regarding how AEL may differentially affect neuromuscular control when compared to CL. Furthermore, the equivocal findings regarding the efficacy of AEL make it difficult for exercise professionals to decide if they should employ AEL with their athletes or patients and during which training phase this type of resistance exercise could be implemented. Therefore, the aims of this thesis were: (i) to examine differences in acute neuromuscular, kinetic, and kinematic responses between AEL and CL during both lower-body single-joint resistance exercise and multiple-joint free weight resistance exercise; (ii) to assess acute force production and contractile characteristics following AEL and CL conditions; (iii) to investigate the influence of eccentric phase velocity (and time under tension) on acute force production and contractile characteristics following AEL and CL conditions; and (iv) to compare common drive and motor unit firing rate responses after single- and multiple-joint AEL and CL. Before investigating neuromuscular, kinetic, and kinematic responses to AEL it was deemed necessary to evaluate normalisation methods for a multiple-joint free weight resistance exercise that would permit the implementation of AEL. Therefore, the aim of the first study of the thesis was to evaluate voluntary maximal (dynamometer- and isometric squat-based) isometric and submaximal dynamic (60%, 70%, and 80% of three repetition maximum) electromyography (EMG) normalisation methods for the back squat resistance exercise. The absolute reliability (limits of agreement and coefficient of variation), relative reliability (intraclass correlation coefficient), and sensitivity of each method was assessed. Strength-trained males completed four testing sessions on separate days, the final three test days were used to evaluate the different normalisation methods. Overall, dynamic normalisation methods demonstrated better absolute reliability and sensitivity for reporting vastus lateralis and biceps femoris EMG compared to maximal isometric methods. Following the methodological study conducted in Chapter 2, the next study began to address the main aims of the thesis. The purpose of the third chapter of the thesis was to compare acute neuromuscular, kinetic, and kinematic responses between single-joint AEL and CL knee extension efforts that included two different eccentric phase velocities. Ten males who were completing recreational resistance exercise attended four experimental test day sessions where knee extension repetitions (AEL or CL) were performed at two different eccentric phase velocities (2 or 4 s). Elevated vastus lateralis eccentric neuromuscular activation was observed in both AEL conditions (p= 0.004, f= 5.73). No differences between conditions were detected for concentric neuromuscular or concentric kinematic variables during knee extension efforts. Similarly, no differences in after-intervention rate of torque development or contractile charactersitics were observed between conditions. To extend the findings of the third chapter of the thesis and provide mechanistic information regarding how AEL may differentially effect acute neuromuscular variables that have been reported to be undergo chronic adaptations, additional measures that were taken before and after the intervention described in the previous chapter were analysed. Therefore, the purpose of the fourth chapter of the thesis was to compare motor unit firing rate and common drive responses following single-joint AEL and CL knee extension efforts during a submaximal isometric knee extension trapezoid force trace effort. In addition, motor unit firing rate reliability during the before-intervention trapezoid force trace efforts was assessed. No differences in the maximum number of detected motor units were observed between conditions. A condition-time-point interaction effect (p= 0.025, f= 3.65) for firing rate in later-recruited motor units occurred, with a decrease in firing rate observed in after-intervention measures in the AEL condition that was completed with a shorter duration eccentric phase. However, no differences in common drive were detected from before- to after-intervention measures in any of the conditions. The time period toward the end of the plateau phase of before-intervention trapezoid force trace efforts displayed the greatest absolute and relative reliability and was therefore used for motor unit firing rate and common drive analysis. The purpose of the fifth chapter was to compare acute neuromuscular and kinetic responses between multiple-joint AEL and CL back squats. Strength-trained males completed two experimental test day sessions where back squat repetitions (AEL or CL) were performed. Neuromuscular and kinetic responses were measured during each condition. No differences in concentric neuromuscular or concentric kinetic variables during back squat repetitions were detected between conditions. Elevated eccentric phase neuromuscular activation was observed during the AEL compared to the CL condition in two to three of the four sets performed for the following lower-body muscles: (i) vastus lateralis (p< 0.001, f= 15.58); (ii) vastus medialis (p< 0.001, f= 10.77); (iii) biceps femoris (p= 0.003, f= 6.10); and (iv) gluteus maximus (p= 0.001, f= 7.98). There were no clear differences in terms of the neuromuscular activation contributions between muscles within AEL or CL conditions during eccentric or concentric muscle actions. Following the investigation of acute motor unit firing rate and common drive responses to lower limb single-joint AEL and CL in the fourth chapter of the thesis, the question arose as to whether or not similar responses would occur in a more complex model, such as a multiple-joint resistance exercise. Multiple-joint resistance exercise poses different neuromuscular activation, coordination, and stabilisation demands. Therefore, the purpose of the sixth chapter of the thesis was to compare acute motor unit firing rate and common drive responses following multiple-joint lower-body free weight AEL and CL.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

Women have higher rates of noncontact musculoskeletal injuries compared to men, as well as at certain times in their menstrual cycles compared to others. The purpose of this study was two-fold: i) to examine the neuromuscular activation patterns of trunk musculature between men and women and ii) within women at different times in their menstrual cycle, during the trunk stability test (TST). The TST is a dynamic lower limb exercise that challenged the trunk musculature to maintain lumbopelvic stability. Surface electromyograms for 24 muscle sites and three-dimensional pelvic motion data were collected during the TST for 18 male and 19 female subjects, as well as for nine female subjects at different times in their menstrual cycles. Through analysis of amplitude and temporal characteristics of the EMG waveforms it was determined that women respond to the TST task with a less coordinated response than men, mainly relying on more co-activation. It was further determined that women have differences in their neuromuscular control patterns during the TST at different points in their menstrual cycle.

The visual grasp reflex provides automatic orienting of gaze (the visual axis in space) to novel visual stimuli. Previous studies have demonstrated activation of neck muscles of awake monkeys appearing at a short fixed latency (55 to 95 ms) after visual target presentation, regardless of whether or when saccades are made. The purpose of these early visually-driven muscle activations may be to prime head rotation required as a part of the coordinated eye-head movement to the target. Similar orienting responses might be found for visually guided reaching. Here, we explore early visually-driven muscle activations of the human upper limb immediately preceding planar reaching movements. Subjects performed reaches towards small visual peripheral targets while upper limb kinematics were recorded and intramuscular electromyography was collected from four shoulder and elbow muscles. Subjects maintained their right hand at a central fixation marker that was extinguished for a gap period (200 ms) prior to appearance of a peripheral target. Subjects were instructed to reach to the target as quickly as possible. Some subjects exhibited a short burst of muscle activity (about 20 ms duration) time-locked to visual target onset. This burst occurred around 85 ms to 105 ms after target onset and preceded the onset of muscle activity associated with volitional arm motion by about 100 ms. Notably, this burst was dependent on target location: visually-driven muscle activity occurred in right shoulder extensor muscles for rightward targets and was absent for leftward targets. In order to better dissociate the visual burst from volitional motor activity, we employed a delay paradigm. No time-locked muscle activity was present in the delay task either after the target appeared or after the fixation marker was extinguished. This suggests that the visual burst is dependent on the imminence of voluntary movement and the laterality of the target. We conclude that the appearance of a visual target can result in short-latency activity on the arm musculature that is appropriate for orienting the arm to the target. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2007-09-27 09:42:55.337

The purposes of the present work were: 1) to develop a computerized model that could predict the personal lift-assist device (PLAD) spring excursion and control spring stiffness for various individuals based on their anthropometry and working posture and 2) to test the PLAD’s (Version 6) effectiveness and user acceptability during static forward bending in an automotive assembly plant. Study 1 required 30 subjects to carry out a protocol that simulated unloaded stoop, squat, and freestyle lifting. Trunk inclination and knee angles were determined via 3 FastrakTM sensors, whereas a displacement transducer attached in-line with the PLAD determined excursion when the trunk or knees flexed. A model was created to determine spring excursion, and it was successfully validated with 10 additional subjects. A computerized model applying the excursion model and mathematical equations was also developed to calculate the required spring stiffness for offsetting a proportion of the L4/L5 bending moment for each individual in various postures. Study 2 investigated the effectiveness and user acceptability of the PLAD at an automotive manufacturing facility, using operators who performed an assembly process requiring forward bending and static holds. Surface EMG data were collected at six sites on the low back and abdomen, and a tri-axial accelerometer was mounted on each subject’s sternum to measure trunk inclination. A 20% reduction in the L4/L5 bending moment was provided to each wearer using the aforementioned computerized model. The PLAD was able to significantly reduce low back muscular activity, predicted-compression, and ratings of perceived exertion, without significantly changing abdominal activity or trunk inclination. Workers had positive opinions about the device, and 80% said they would wear the device everyday on-line. Additionally, the computerized model developed in Study 1 was effective, as worker low back muscular activity was reduced by approximately 20% when wearing the PLAD. With slight alterations, the PLAD appears to be beneficial in reducing low back forces and discomfort in many tasks that place excessive biomechanical loading on the low back. / Thesis (Master, Kinesiology & Health Studies) -- Queen's University, 2008-08-18 15:55:16.757

The wrist extensor muscles have been implicated in a work-related upper limb disorder referred to as non-specific arm pain (NSAP), which has an unknown pathophysiology. The primary objective of this thesis was to perform an electrophysiological evaluation of NSAP to gain a better understanding of the underlying pathophysiology. Secondary objectives were to determine the utility and reliability of the decomposition-based quantitative electromyography (DQEMG) system used to examine NSAP. The utility of the DQEMG system was first tested to determine whether physiological changes in muscles of healthy individuals performing low-level fatiguing contractions could be detected using this approach. Next, the reliability of the outcome variables produced through this system was tested on healthy individuals performing low-level non-fatiguing contractions. A case-control study was then performed using DQEMG to determine whether there were measurable changes in electrophysiological variables that suggest whether NSAP is myopathic or neuropathic in nature. Finally, the case control study was repeated using a less invasive approach of electrophysiological evaluation to determine if this method might be equally useful in determining the pathophysiology of NSAP. Results revealed DQEMG can be effectively and reliably used to detect changes in the physiological characteristics of motor units that accompany fatigue. Specifically, decreases in mean motor unit firing rates along with increases in amplitude, duration, and area parameters of needle- and surface-detected motor unit potentials (MUPs) suggest that recruitment is a main cause of increased electromyographic amplitude parameters with fatigue. Results of the reliability study suggested that DQEMG provides sufficiently consistent results to allow it to be effectively used for quantitative electromyographic (QEMG) analysis. In the first case control study, the QEMG parameters suggested that the underlying pathophysiology in NSAP may be myopathic in nature; specifically, QEMG findings for the NSAP group revealed smaller MUPs compared to the other groups. Lastly, the case control study using spike shape analysis across different levels of isometric wrist extension contractions was deemed to be useful in determining differences among the groups. This research suggests that NSAP may be myopathic in nature, since the NSAP group showed significantly lower mean spike amplitude and mean spike slope values compared to healthy subjects. / Thesis (Ph.D, Rehabilitation Science) -- Queen's University, 2008-08-27 14:53:55.892