Effects of postural threat on the scaling of anticipatory postural adjustments in young and older adults.

Introduction: The ability to scale anticipatory postural adjustments (APAs) according to the predicted size of the upcoming movement is reduced with aging. While age-related changes in central set may be one reason for this effect, an individual's emotional state might also contribute to changes in anticipatory postural control. Therefore, the purpose of this study was to determine whether an altered emotional state, as elicited through postural threat, alters the scaling of APAs during a handle pull movement in young and older adults.

Postural threat increases sample entropy of postural control.

Introduction: Postural threat elicits modifications to standing balance. However, the underlying neural mechanism(s) responsible remain unclear. Shifts in attention focus including directing more attention to balance when threatened may contribute to the balance changes.

The effect of acute low-load resistance exercise with the addition of blood flow occlusion on muscle function in boys and men.

Purpose: In adults, low-load resistance training with blood flow occlusion (BFO) mimics strength increases that occur from high-load training, without the need to experience high mechanical stress. In view of child-adult differences in exercise responses, this study examined whether BFO during exercise elicits differential changes in maximal voluntary contraction (MVC) and electromyographical (EMG) activity in children and adults.

Methods: Sixteen men (24.

The effects of perturbation type and direction on threat-related changes in anticipatory postural control.

The purpose of this study was to determine whether the type and direction of postural perturbation threat differentially affect anticipatory postural control. Healthy young adults stood on a force plate fixed to a translating platform and completed a series of rise-to-toes movements without (No Threat) and with (Threat) the potential of receiving a postural perturbation to either their feet (15 participants) or torso (16 participants). Each type of perturbation threat was presented along the anteroposterior (A-P) or mediolateral (M-L) axis.

Motor learning induces time-dependent plasticity that is observable at the spinal cord level.

Key Points: The spinal cord is an important contributor to motor learning It remains unclear whether short-term spinal cord adaptations are general or task-specific Immediately after task acquisition, neural adaptations were not specific to the trained task (i.e. were general) Twenty-four hours after acquisition, neural adaptations appeared to be task-specific The neural reorganization and generalization of spinal adaptations appears to be time-dependent.

The effects of distraction on threat-related changes in standing balance control.

Research indicates that threat-induced changes in standing balance are associated with shifts in attention focus. This study investigated whether distracting attention modifies threat-induced changes in standing balance. Twenty-five healthy young adults stood without (No Threat) and with (Threat) the possibility of receiving a temporally unpredictable anteroposterior support surface translation.

Examining changes in corticospinal excitability and balance performance in response to social-comparative feedback.

Background: Social-comparative feedback informs an individual that their performance was better or worse than the group. Previous studies have found that compared to knowledge of results alone, social-comparative feedback produces a valence response that results in larger improvements in balance performance. However, the neural processes contributing to these motor improvements have not yet been examined.

Isometric-based test improves EMG-threshold determination in boys vs. men.

Background: Children have been hypothesized to utilize higher-threshold (type-II) motor units (MUs) to a lesser extent than adults. Two recent studies, using a cycling-based EMG-threshold (EMG) protocol, supported the hypothesis, showing children's EMG intensities to be higher than adults'. Conclusions, however, were hampered by children's low EMG detection rates.

Repeated exposure to the threat of perturbation induces emotional, cognitive, and postural adaptations in young and older adults.

Threat-related changes in postural control and their associations with changes in emotional and cognitive states are influenced by postural threat experience, however, limited work has explored individuals' capacity to adapt threat-related responses over longer periods of threat exposure. This study examined the effects of initial and repeated postural threat exposure on emotional, cognitive, and postural responses. Twenty-seven young and twenty-seven older adults stood on a force plate fixed to a translating platform.

Age-related reversal of spinal excitability during anticipatory postural control.

Introduction: An internal perturbation of standing balance activates muscles critical for maintaining balance and is preceded by anticipatory postural adjustments (APAs). In healthy younger adults, a measure of spinal excitability in the form of the Hoffmann (H) reflex becomes depressed during APAs but how aging affects the reflex control of APAs is unknown.

Methods: We compared H reflex excitability profiles in the right soleus muscle, indirectly indicating APA, between younger (n = 11, age 19-24 years), middle-aged (n = 10, age 37-56 years), and older healthy adults (n = 11, age 63-78 years).

Alterations in the cortical control of standing posture during varying levels of postural threat and task difficulty.

Cortical excitability increases during the performance of more difficult postural tasks. However, it is possible that changes in postural threat associated with more difficult tasks may in themselves lead to alterations in the neural strategies underlying postural control. Therefore, the purpose of this study was to examine whether changes in postural threat are responsible for the alterations in corticospinal excitability and short-interval intracortical inhibition (SICI) that occur with increasing postural task difficulty.

Effects of Plyometric and Resistance Training on Muscle Strength, Explosiveness, and Neuromuscular Function in Young Adolescent Soccer Players.

McKinlay, BJ, Wallace, P, Dotan, R, Long, D, Tokuno, C, Gabriel, D, and Falk, B. Effects of plyometric and resistance training on muscle strength, explosiveness, and neuromuscular function in young adolescent soccer players. J Strength Cond Res 32(11): 3039-3050, 2018-This study examined the effect of 8 weeks of free-weight resistance training (RT) and plyometric (PLYO) training on maximal strength, explosiveness, and jump performance compared with no added training (CON), in young male soccer players.

Exploring the relationship between threat-related changes in anxiety, attention focus, and postural control.

Individuals report directing attention toward and away from multiple sources when standing under height-related postural threat, and these changes in attention focus are associated with postural control modifications. As it is unknown whether these changes generalize to other types of threat situations, this study aimed to quantify changes in attention focus and examine their relationship with postural control changes in response to a direct threat to stability. Eighty young adults stood on a force plate fixed to a translating platform.

The medium latency muscle response to a vestibular perturbation is increased after depression of the cerebellar vermis.

Introduction: Galvanic vestibular stimulation (GVS) is able to evoke distinct responses in the muscles used for balance. These reflexes, termed the short (SL) and medium latency (ML) responses, can be altered by sensory input; decreasing in size when additional sensory cues are available. Although much is known about these responses, the origin and role of the responses are still not fully understood.

Preparatory cortical and spinal settings to counteract anticipated and non-anticipated perturbations.

Little is known about how the central nervous system prepares postural responses differently in anticipated compared to non-anticipated perturbations. To investigate this, participants were exposed to translational and rotational perturbations presented in a blocked (anticipated) and a random (non-anticipated) design. The preparatory setting ('central set') was measured by H-reflexes, motor-evoked potentials (MEPs), and short-interval intracortical inhibition (SICI) shortly before perturbation onset in the soleus of 15 healthy adults.

Does spinal excitability scale to the difficulty of the dual-task?

Purpose: This study examined whether spinal excitability, as measured by the soleus Hoffmann reflex (H-reflex), is scaled to the difficulty level of the dual-task being performed.

Methods: Twenty-two participants completed a combination of three balance task and three secondary cognitive (visuo-motor) task difficulty levels for a total of nine dual-task conditions. An additional eight participants were tested while performing the same three balance task difficulty levels on its own (i.

The effects of foot cooling on postural muscle responses to an unexpected loss of balance.

The purpose of this study was to examine the role of foot sole somatosensory information during reactive postural control. Twenty young adults (22.0±1.

Isometric and dynamic strength and neuromuscular attributes as predictors of vertical jump performance in 11- to 13-year-old male athletes.

In explosive contractions, neural activation is a major factor in determining the rate of torque development, while the latter is an important determinant of jump performance. However, the contribution of neuromuscular activation and rate of torque development to jump performance in children and youth is unclear. The purpose of this study was to examine the relationships between the rate of neuromuscular activation, peak torque, rate of torque development, and jump performance in young male athletes.

The threat of a support surface translation affects anticipatory postural control.

This study examined how postural threat in the form of a potential perturbation affects an individual's ability to perform a heel raise. Seventeen adults completed three conditions: i) low threat, where participants performed a heel raise in response to a "go" tone, ii) high threat, where participants either heard the same "go" tone, for which they performed a heel raise, or experienced a support surface translation in the medio-lateral direction that disturbed their balance, and iii) choice reaction time task, where participants either completed a heel raise in response to the same "go" tone or a toe raise in response to a lower pitched tone. For all heel raise trials, anticipatory postural adjustments (APAs) were quantified from center of pressure (COP) recordings and electromyographic (EMG) activity from the tibialis anterior (TA) and soleus (SOL).

The direction of the postural response to a vestibular perturbation is mediated by the cerebellar vermis.

When an electrical stimulus is applied to perturb the vestibular system, a postural response is generated orthogonal to head orientation. It has previously been shown that there is a convergence of neck proprioceptive and vestibular input within the cerebellum to provide a head-on-body reference frame (Manzoni et al. in Neuroscience 93:1095-1107, 1999).

The Electromyographic Threshold in Girls and Women.

Background: The electromyographic threshold (EMG) is thought to reflect increased high-threshold/type-II motor-unit (MU) recruitment and was shown higher in boys than in men. Women differ from men in muscular function.

Purpose: Establish whether females' EMG and girls-women differences are different than males'.

Corticospinal excitability is associated with hypocapnia but not changes in cerebral blood flow.

Key Points: Reductions in cerebral blood flow (CBF) may be implicated in the development of neuromuscular fatigue; however, the contribution from hypocapnic-induced reductions (i.e. P ETC O2) in CBF versus reductions in CBF per se has yet to be isolated.

The effects of dual-tasking on arm muscle responses in young and older adults.

This study examined whether dual-tasking affects an individual's ability to generate arm muscle responses following a loss of balance. Nineteen young and 16 older adults recovered their balance in response to a surface translation. This balance task was either completed on its own or while counting backwards by 2's (easy counting difficulty) or 7's (hard counting difficulty).

The electromyographic threshold in boys and men.

Background: Children have been shown to have higher lactate (LaTh) and ventilatory (VeTh) thresholds than adults, which might be explained by lower levels of type-II motor-unit (MU) recruitment. However, the electromyographic threshold (EMGTh), regarded as indicating the onset of accelerated type-II MU recruitment, has been investigated only in adults.

Purpose: To compare the relative exercise intensity at which the EMGTh occurs in boys versus men.

The influence of instruction on arm reactions in individuals with Parkinson's disease.

The purpose of this study was to examine whether explicit instruction would facilitate arm reactions in individuals with Parkinson's disease (PD). Individuals with (n = 10) and without (n = 15) PD responded to unexpected support-surface translations. To recover their balance, participants were required to either respond naturally (react natural) or to reach toward a nearby handrail (explicit instruction).