Knowledge of repetitions range affects force production in trained females.

Author:Halperin, Israel
Position:Reseach article - Report
 
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Introduction

Pacing strategies refers to the conscious and/or subconscious distribution of energy during physical effort (De Koning et al., 2011; Gibson and Noakes, 2005; Tucker and Noakes, 2009). It has been suggested that such strategies are regulated, and established before the initiation of exercise in order to enhance performance and to avoid depletion of energy resources. By doing so, premature fatigue and injuries can be avoided (Gibson and Noakes, 2005; Noakes, 2012). Furthermore, the chosen pacing strategy is continuously regulated throughout the activity based on external and internal environmental changes such as knowledge of end point (Billaut et al., 2011; Halperin et al., 2014), motivation (Blanchfield et al., 2013; Stone et al., 2012), and core temperature (Tucker et al., 2004; 2006). Despite the growing number of studies of this topic, most have characterized pacing strategies in cyclic activities such as cycling and running utilizing activities lasting over two minutes. More so, it is currently not clear if pacing strategies differ between the genders.

The few studies to date that have measured pacing strategies during short and intense activities found mixed results (Ansley et al., 2004; Billaut et al., 2011; Chidonk et al., 2013; Morton, 2009; Wittekin et al., 2011). Chidnok et al. (2013) compared two repetitions of threeminute high intensity cycling bouts: self-paced and constant work. Exhaustion with both trials was correlated with the same peak V[O.sub.2] and thus was highly dependent on peripheral physiological processes, rather than a self selected pacing strategy. In contrast, Wittekin et al. (2011) used four maximal cycling sprints of 5 s, 15 s, 30 s and 45 s durations. Power was significantly higher during the five and 15 s bouts compared to the first 10 s of the 45 s bout supporting an anticipatory response. Ansley et al. (2004) asked subjects to perform four 30 s, one 33 s and one 36 s cycling tests. However, they were deceived about the duration and actually completed two bouts each of 30 s, 33 s, and 36 s. Power was lower during the last six seconds of the 36 s deception test compared to the actual 36 s test supporting an anticipatory response. By manipulating a clock to run 10% faster or slower than the control condition, males cycled significantly longer when the clock ran slower, but not the females (Morton, 2009). Billaut et al. (2011) implemented three fatiguing protocols consisting of ten sets of six-second maximal cycling sprints. On the control day, subjects were told they would complete ten sets. On the unknown day, participants were not told how many sets they would complete but were - stopped after ten sets. On the deception day participants were told they would complete five sets, but were then asked to perform five additional sets. Power and work were higher during the first five sets in the deception day compared to both control and unknown days. Halperin et al. (2014) were the first to examine if pacing strategies are employed during maximal voluntary contractions (MVCs) using a similar methodology to Billaut et al. (2011). In the control day subjects were asked to perform twelve MVCs and were stopped after twelve. In the unknown day subjects were not told how MVCs they would perform but were stopped after twelve. In the deception day subjects were told to perform six MVCs, but after the sixth contraction were asked to perform a few more repetitions and were stopped after twelve. Greater forces and higher biceps electromyography (EMG) activity were demonstrated during the deception compared to the unknown condition starting from the first repetition. It was also found that under all conditions the force applied in the last repetition (#12) were significantly greater than the previous. These findings suggest that the anticipation of performing a certain number of MVCs led the subjects to utilize different pacing strategies.

Unfortunately, only two of the above studies included female subjects. Billaut et al. (2011) found that females were susceptible to deception, whereas Morton (2009) found the opposite. Therefore, similar studies using female subjects are warranted. Additionally, other than Halperin et al. (2014) all of the studies used cycling. Hence, it is of interest to examine if females employ similar pacing strategies as males while performing the repeated MVCs protocol (Halperin et al. 2014). Indeed, it has been reported that female fatigue profiles differ from males during repetitive or sustained muscle contractions (Hunter, 2009), and during multiple sprint exercises (Billaut and Bishop, 2009). Females are reported to be more fatigue resistant than males by approximately 23% during sustained isometric contractions of different intensities (Hunter 2009). Suggested factors to explain the gender muscle fatigue differences include differences in central drive (Russ et al., 2003) distribution of muscles fiber types (Miller et al. 1993) and muscle metabolism (Russ et al., 2005).

Therefore, the aim of this study was to determine if females utilize similar pacing strategies to males during repeated MVCs. Using a similar design to Halperin et al. (2014), it was hypothesized that 1) prior knowledge of performing fewer repetitions would lead to greater force and EMG. 2) Not receiving any repetition endpoint would lead to lower values of force and EMG. 3) Informing the participants about their forthcoming last repetition will lead to higher force and EMG values.

Methods

Participants

Twenty females (22 [+ or -] 4 years, 1.68 [+ or -] 0.05 m, 60 [+ or -] 8 kg) participated in this study. Subjects were healthy and performed resistance training a minimum of twice a week for at least a year prior to participation in the study. Subjects were asked to avoid a heavy meal and caffeinated drinks three hours before the test. Furthermore, they were requested to avoid upper body training a day prior to testing days, and avoid all types of training on testing days. McLester et al. (2003) demonstrated that a single rest day was sufficient to fully recover between two similar strength training sessions consisting of three sets of 10 repetitions to failure...

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