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Robin Healy, Ian C. Kenny, and Andrew J. Harrison

accomplish this, the concept of reactive strength was developed. 6 Reactive strength has been described in numerous ways throughout the literature. The most commonly used definition is the capacity of an athlete to bear a stretch load and subsequently switch rapidly from an eccentric to concentric muscle

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Nabil Ilmane and Jacques LaRue

The aim of this experiment was to explore the behavioral effects of various temporal pressures on the anticipatory postural adjustments (APAs) in a complex task. Eighteen handball players performed a handball direct throw in three conditions of temporal pressure: (1) a reactive condition (RC), the throw was initiated as quickly as possible following a visual stimulus; (2) an anticipation-coincidence condition (AC), by synchronizing the impact of the ball with the passage of a visual mobile on a target; and (3) a self-initiated (SI) throw. The whole-body postural oscillation and the acceleration of the wrist were measured before and during the throwing action. Results showed that the delays between the onsets of the postural and focal activities were significantly different between RC and both the SI and the AC conditions. Movement time, time to peaks (negative and positive), are shorter in the RC, intermediate in the AC, and longer in the SI condition. Variability was significantly larger in AC in comparison with RC and SI. These results support the existence of different control modes triggered by the temporal pressure; they demonstrate that these control modes can be generalized to complex intentional movements such as the throwing skill and to an anticipation-coincidence situation.

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Ella McLoughlin, Rachel Arnold, Paul Freeman, James E. Turner, Gareth A. Roberts, David Fletcher, George M. Slavich, and Lee J. Moore

(e.g., genetics), cumulative lifetime stressor exposure (e.g., past and current stressors), and protective factors (e.g., social, psychological, and behavioral processes); (b) psychophysiological stress responses (e.g., cognitive appraisals and cardiovascular reactivity); and (c) biological aging and

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Kristof Kipp, Michael T. Kiely, Matthew D. Giordanelli, Philip J. Malloy, and Christopher F. Geiser

The Reactive Strength Index (RSI) is a measure often used to quantify dynamic lower-extremity performance during a drop jump (DJ). 1 – 3 The RSI represents a highly reliable (ie, intraclass correlation coefficient > .90) and simple index of performance that is also easy to measure and interpret. 4

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Xihe Zhu and Justin A. Haegele

Wearable devices such as accelerometers and pedometers are commonly used in research to measure physical activity ( Cain, Sallis, Conway, Van Dyck, & Calhoon, 2013 ). One concern with using wearable devices is reactivity, which refers to the phenomenon in which research participants alter their

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Michelle R. Tanel, Tyler B. Weaver, and Andrew C. Laing

control), the size of the base of support must be increased. Following external postural perturbations (eg, a simulated trip), older adults commonly respond with 1 or more reactive steps. 12 , 13 Increased step length has been demonstrated to enhance balance control abilities 14 ; however, older adults

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Brian M. Moore, Joseph T. Adams, Sallie Willcox, and Joseph Nicholson

to rapidly and appropriately generate corrective muscle forces to recover from imbalance ( Jacobs & Horak, 2007 ; Shumway-Cook & Woollacott, 2017 ). Such reactions are referred to as compensatory or reactive postural responses, defined as the ability to recover from instability through a rapid

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Jorg Teichmann, Kim Hébert-Losier, Rachel Tan, Han Wei Lem, Shabana Khanum, Ananthi Subramaniam, Wee-Kian Yeo, Dietmar Schmidtbleicher, and Christopher M. Beaven

identified as being associated with knee valgus angles during cutting movements 19 and performance indicators in contact sport 20 in high-level athletes. Thus, we hypothesized that a reactive strength metric obtained from a unilateral DJ may provide a more relevant and informative metric to assess

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Shani Batcir and Itshak Melzer

.g., push, slip, trip; Maki & McIlroy, 1997 ). Unexpected loss of balance triggers a series of balance reactive responses that are not under volitional control, which act to quickly restore equilibrium ( Nashner 1976 , 1977 , 1980 ). When these reactive responses are not effective, they might cause a fall

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Tyler M. Saumur, Jacqueline Nestico, George Mochizuki, Stephen D. Perry, Avril Mansfield, and Sunita Mathur

Reactive balance control is necessary for maintaining or regaining stability following a balance perturbation. 1 Reactive balance control involves the activation of trunk and lower limb muscles. 2 , 3 Accordingly, muscle strength is commonly studied in the context of balance control. Muscle