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Objective This study aimed to investigate how load expectations modulate neuromuscular and postural strategies in the anticipation of a freestyle lifting task with varying expected loads in individuals with and without chronic low back pain (cLBP). Methods Forty-seven participants, 28 with cLBP pain and 19 without, were recruited and completed a series of freestyle lifting trials (3 sets of box lifted for a total of 36 lifts). Verbal cues were used to modulate their expectations about the boxes’ weight: no expectation, lighter or heavier load expectations. Following each set, participants rated their perceived exertion on a visual analog scale. During the lifting protocol, kinematics (time to maximal flexion, angular velocity and joint angles), electromyography muscle activity (erector spinae and quadriceps) and center of pressure displacement were simultaneously recorded. Results Results showed that time to maximal knee flexion was modulated by load expectations in both groups (mean lighter load expectations = 1.15 ± 0.32 sec.; mean heavier load expectations = 1.06 ± 0.31 sec.). Results also showed a load expectations X group interaction for that time to maximal hip and lumbar flexion. Time to maximal hip flexion decreased with heavier load expectations (mean lighter load expectations = 1.20 ± 0.36; mean heavier load expectations = 1.16 ± 0.33) for cLBP only. Time to maximal lumbar flexion increased with heavier load expectation (mean lighter load expectations = 1.41 ± 0.27 sec.; mean lighter load expectations = 1.46 ± 0.29 sec.) for participants without LBP. However, no difference in lumbar, hip nor knee angles were observed between groups or conditions. Results highlighted significant load expectation effects for erector spinae electromyography activity, as lower muscle activations was observed for both groups with heavier load expectations (mean = 0.32 ± 0.15), compared to lighter load expectations (mean = 0.52 ± 0.27). Force plates analyses did not reveal any significant load expectation effects. Conclusion Present findings showed that load expectations modulate movement strategies and muscle activation similarly but not identically in individuals with chronic low back pain and healthy adults during freestyle lifting. Results of the present study partially differ from previous studies and suggest only minor differences in lifting strategies between healthy individuals and individuals with cLBP experiencing low level of pain and disability. More studies are needed to investigate the potential role of load expectations in the development and persistence of chronic low back pain.

People usually move at a self-selected pace in everyday life. Yet, the principles underlying the formation of human movement vigour remain unclear, particularly in view of intriguing inter-individual variability. It has been hypothesized that how the brain values time may be the cornerstone of such differences, beyond biomechanics. Here, we focused on the vigour of self-paced reaching movement and assessed the stability of vigour via repeated measurements within participants. We used an optimal control methodology to identify a cost of time (CoT) function underlying each participant’s vigour, considering a model of the biomechanical cost of movement. We then tested the extent to which anthropometric or psychological traits, namely boredom proneness and impulsivity, could account for a significant part of inter-individual variance in vigour and CoT parameters. Our findings show that the vigour of reaching is largely idiosyncratic and tend to corroborate a relation between the relative steepness of the identified CoT and boredom proneness, a psychological trait relevant to one’s relationship with time in decision-making.

The primary aim of this study was to determine whether the levels of obsessive passion (OP) and harmonious passion for a suspended leisure activity contribute to pain catastrophizing and pain intensity in patients undergoing the rehabilitation process. The secondary aim was to examine whether the levels of passion associated with a maintained leisure activity offset the contribution of having a leisure activity suspended to pain intensity and catastrophizing. Ninety-one outpatients from functional rehabilitation units (Mage=37, SD=13.44 years) completed measures of pain catastrophizing, pain intensity, and passion about valued leisure activities (one they were prevented from practicing and one they remained able to practice). Correlation analysis showed that the level of OP for a suspended valued leisure activity was positively associated with pain catastrophizing and pain intensity. Results showed that pain catastrophizing mediated the relationship between this level of passion and pain intensity. The levels of harmonious passion and OP for a maintained valued leisure activity did not offset the contribution of OP for a suspended leisure activity to pain-related outcomes. When prevented from practicing a valued leisure activity, only OP contributes to the prediction of pain catastrophizing and pain intensity. The contribution of pain catastrophizing provides a potential explanation for why the level of OP for a suspended leisure activity is related to pain intensity ratings. The benefits of maintaining a valued leisure activity during rehabilitation do not seem sufficient to counterbalance the maladaptive effects of being prevented from the practice of a previous/another valued leisure activity.

Movement vigor is an important feature of motor control that is thought to originate from cortico-basal ganglia circuits and processes shared with decision-making, such as temporal reward discounting. Accordingly, vigor may be related to one’s relationship with time, which may, in turn, reflect a general trait-like feature of individuality. While significant interindividual differences of vigor have been typically reported for isolated motor tasks, little is known about the consistency of such differences across tasks and movement effectors. Here, we assessed interindividual consistency of vigor across reaching (both dominant and nondominant arm), walking, and gazing movements of various distances within the same group of 20 participants. Given distinct neural pathways and biomechanical specificities of each movement modality, a significant consistency would corroborate the trait-like aspect of vigor. Vigor scores for dominant and nondominant arm movements were found to be highly correlated across individuals. Vigor scores of reaching and walking were also significantly correlated across individuals, indicating that people who reach faster than others also tend to walk faster. At last, vigor scores of saccades were uncorrelated with those of reaching and walking, reaffirming that the vigor of stimulus-elicited eye saccades is distinct. These findings highlight the trait-like aspect of vigor for reaching movements with either arms and, to a lesser extent, walking. NEW & NOTEWORTHY Robust interindividual differences of movement vigor have been reported for arm reaching and saccades. Beyond biomechanics, personality trait-like characteristics have been proposed to account for those differences. Here, we examined for the first time the consistency of interindividual differences of vigor during dominant/nondominant arm reaching, walking, and gazing to assess the trait-like aspect of vigor. We found a significant consistency of vigor within our group of individuals for all tested tasks/effectors except saccades.

Background.Through real-time behavioral observation systems, pain behaviors are commonly used by clinicians to estimate pain intensity in patients with low back pain. However, little is known about how clinicians rely on pain-related behaviors to make their judgment. According to the Information Integration Theory (IIT) framework, this study aimed at investigating how clinicians value and integrate information from lumbopelvic kinematics (LK), a protective pain behavior, and facial expression intensity (FEI), a communicative pain behavior, to estimate pain in patients with chronic low back pain (cLBP).Methods.Twenty-one experienced clinicians and twenty-one novice clinicians were asked to estimate back pain intensity from a virtual character performing a trunk flexion-extension task.Results.Results revealed that both populations relied on facial expression and that only half of the participants in each group integrated FEI and LK to estimate cLBP intensity. Among participants who integrated the two pain behaviors, averaging rule predominated among others. Results showed that experienced clinicians relied equally on FEI and LK to estimate pain, whereas novice clinicians mostly relied on FEI.Discussion.The use of additive rule of integration does not appear to be systematic when assessing others’ pain. When assessing pain intensity, communicative and protective pain behaviors may have different relevance.

Epub 2015 Oct 26. Erratum in: Exp Brain Res. 2016 Apr.; This study explored the directional specificity of fear of falling (FoF) effects on the stabilizing function of anticipatory postural adjustments (APA). Participants (N = 71) performed a series of lateral leg raises from an elevated surface in three conditions: in the "Control condition", participants stood at the middle of the surface; in the two test conditions, participants were positioned at the lateral edge of the surface so that the shift of the whole-body centre-of-mass during APA for leg raising was directed towards the edge ("Approach condition") or was directed away from the edge ("Avoidance condition"). Results showed that the amplitude of APA was lower in the "Approach condition" than in the "Control condition" (p < .01); this reduction was compensated for by an increase in APA duration (p < .05), so that both postural stability and motor performance (in terms of peak leg velocity, final leg posture and movement duration) remained unchanged. These changes in APA parameters were not present in the "Avoidance condition". Participants further self-reported a greater FoF (p < .001) and a lower ability to avoid a fall (p < .001) in the "Approach condition" (but not in the "Avoidance condition") than in the "Control condition". The results of this study show that the effects of FoF do not solely depend on initial environmental conditions, but also on the direction of APA relative to the location of the postural threat. These results support the so-called Motivational Direction Hypothesis, according to which approach and avoidance behaviours are primed by emotional state.

Objective Although audio and visual information constitute relevant channels to communicate pain, it remains unclear to what extent observers combine and weight these sources of information when estimating others' pain. The present study aimed to examine this issue through the theoretical framework of the Information Integration Theory. The combination and weighting processes were addressed in view of familiarity with others' pain. Method Twenty-six participants familiar with pain (novice podiatry clinicians) and thirty non-specialists were asked to estimate the level of pain associated with different displayed locomotor behaviors. Audio and visual information (i.e., sound and gait kinematics) were combined across different intensities and implemented in animated human stick figures performing a walking task (from normal to pathological gaits). Results The novice clinicians and non-specialists relied significantly on gaits and sounds to estimate others' pain intensity. The combination of the two types of information obeyed an averaging rule for the majority of the novice clinicians and an additive rule for the non-specialists. The novice clinicians leaned more on gaits in the absence of limping, whereas they depended more on sounds in the presence of limping. The non-specialists relied more on gaits than on sounds. Overall, the novice clinicians attributed greater pain levels than the non-specialists did. Conclusion Depending on a person's clinical experience, the combination of audio and visual pain-related behavior can qualitatively change the processes related to the assessment of others' pain. Non-verbal pain-related behaviors as well as the clinical implications are discussed in view of the assessment of others' pain.

Objectives The main goal of this study was to determine to what extent load expectations modulate neuromechanical adaptations in individuals with and without chronic low back pain (cLBP) when lifting and lowering various loads. The second goal was to assess the feasibility of a simple lifting protocol during which expectations about loads were manipulated. Methods Seventeen participants with cLBP and 18 participants without low back pain were asked to lift and lower boxes of mild to moderate loads. Two kinds of expectations (lighter and heavier) were respectively associated to each experimental block. Self-reported exertion was assessed to control for expectations modulation. Erector spinae and vastus lateralis electromyography (EMG) activity were recorded and kinematics angle calculated. Results The results showed a main effect of expectations, with loads introduced as heavier being associated to a higher exertion compared with loads introduced as lighter. EMG activity analyses revealed significant interaction involving expectations, movement phase, and loads, as well as significant differences between groups. Kinematic angles did not reveal any significant effect of expectations nor group during the lifting phase. Conclusions Psychological factors may contribute to neuromechanical adaptations to low back pain. Our preliminary findings show that expectations about loads may result in neuromechanical differences between individuals with cLBP and those without cLBP. This pilot study showed that testing the manipulation of expectations and EMG records was feasible but highlighted the need to go beyond single infrared markers to assess kinematics.

International audience; This research investigated whether and how self-determined motivation predicts perceived susceptibility to injury during competition (marathon). Two correlational studies including 378 (Study 1) and 339 (Study 2) marathon runners were conducted. Participants filled out a questionnaire the day before the race measuring self-determined motivation, perceived susceptibilities to marathon-related injury and to keep running through pain, and control variables. Study 1 showed that self-determined motivation was negatively related to perceived susceptibility to marathon-related injury. Study 2 replicated this finding and showed that this relationship was partially mediated by perceived susceptibility to keep running through pain during the race. Moreover, results indicated that the predictive role of self-determination was mostly driven by controlled forms of motivation, and more particularly external regulation. These results suggest that self-determined motivation for sport is a protective factor of injury.

This study examined how pleasant and unpleasant emotional states influence the biomechanical organization of both forward and backward step initiation (SI). Participants (N = 31) purposely took a single step toward or away from a screen following the presentation of a pleasant (erotic), unpleasant (mutilation) or neutral (objects and landscapes) image. The main results showed that the reaction time for forward SI was shortened when individuals were exposed to pleasant pictures as compared with unpleasant pictures. The anticipatory whole-body center-ofmass velocity associated with backward SI, as well as the peak of center-of-mass velocity associated with forward SI both reached lower values when individuals were exposed to pleasant pictures as compared with neutral pictures. In contrast, unpleasant pictures did not significantly induce any change in the forward or backward SI parameters. Overall, these results obtained for whole-body approach/avoidance-like behaviors provided mitigated support for the so-called “motivational direction hypothesis.”

Drawing upon both heuristic- and threat-based approaches, we sought to examine whether perceived similarity with injury-prone people and perceived control over injury occurrence would directly contribute to perceived risk and whether these variables would mediate the previous injury-perceived risk relationship. Judokas (n = 207) reported the number of injuries experienced in the past year and then completed measures of perceived similarity, perceived control, and injury risk perception. Analyses revealed that perceived similarity and perceived control directly contributed to perceived risk of injury; only perceived similarity acted as a partial mediator of the injury-perceived risk relationship. These findings are discussed in relation to the potential influence of the sport context, which universally involves the acceptance of a high risk of injury.

International audience; During leg flexion from erect posture, postural stability is organized in advance during "anticipatory postural adjustments" (APA). During these APA, inertial forces are generated that propel the centre of gravity (CoG) laterally towards stance leg side. This study examined how fear of falling (FoF) may influence this anticipatory postural control of medio-lateral (ML) stability. Ten young healthy participants performed a series of leg flexions at maximal velocity from low and high surface heights (6 and 66 cm above ground, respectively). In this latter condition with increased FoF, stance foot was placed at the lateral edge of the support surface to induce maximal postural threat. Results showed that the amplitude of ML inertial forces generated during APA decreased with FoF; this decrease was compensated by an increase in APA duration so that the CoG position at time of swing foot-off was located further towards stance leg side. With these changes in ML APA, the CoG was propelled in the same final (unipodal) position above stance foot as in condition with low FoF. These results contrast with those obtained in the literature during quiet standing which showed that FoF did not have any influence on the ML component of postural control. It is proposed that ML APA are modified with increased FoF, in such a way that the risk of a sideway fall induced by the large CoG motion is attenuated.

International audience; Previous studies have shown how social networks lead athletes to accept pain as a "part of the game," which generates pressure on athletes to continue competing despite being in pain. Little is known, however, about the potential coping strategies that are related to pain behavior in sport. This study of 205 combat athletes examined whether pain coping strategies, including distraction from pain, praying, reinterpreting pain sensations, ignoring pain, and pain catastrophizing, are related to athletes' inclination to play through pain. Results revealed that pain catastrophizing led athletes to reduce their physical involvement in their sport activity. Of particular interest was the moderating effect of ignoring pain such that ignoring pain significantly attenuated the negative effect of pain intensity on athletes' inclination to play through pain. Few studies have tested and supported the contribution of pain coping to the prediction of behavior in real sport situations. By identifying which coping strategies athletes could use to maintain their physical involvement despite being in (sometimes intense) pain, the current study makes an important contribution for tailoring pain management programs for this at-risk population.

In-line skating is increasing in popularity with a concomitant raise in the number of injuries associated with this activity. Studies have emphasized the value of protective gears in reducing the incidence of injuries and the subsequent need to identify the factors and processes involved in decision making about safety gear-wearing. The present study examined the contribution of the theory of planned behaviour (TPB) variables, and perceived susceptibility to and perceived severity of skating injury on the safety gear-wearing intention of adult skaters.Skaters (n=181) completed a questionnaire assessing the constructs of the TPB, perceived susceptibility to and perceived severity of skating injuries, and intention to wear safety gear.Hierarchical regression analyses revealed significant contributions of instrumental attitude and subjective norm to the prediction of safety gear-wearing intention. In addition, perceived susceptibility to and perceived severity of injuries enhanced the prediction of intentions to wear safety gear over and above the contribution of TPB components.As the TPB focuses only on behavioural evaluation, it seems promising to include threat perceptions in this theory as another aspect of health-related cognitions motivating intention formation about safety gear use. Practical implications for future campaigns and countermeasures are discussed.