Fatigue

The effect of a specific fatigue protocol in force propulsion and postural sway in female handball athletes

Fatigue is a case of interaction between different factors and is characterized by the increase in the perceived effort to exercise and produce force. However, the effect on balancing tasks are not completely understood, especially the time course of the postural sway parameters during the recovery phase. Twenty female handball athletes participated in this study. They stood upright in a one-leg posture supported by the non-dominant limb on a force plate. The center of pressure (COP) and the maximum propulsion force (FMAX) were obtained at baseline, immediately after the exhaustion due to the fatigue protocol and every minute during the first 10 min of the recovery phase. For the postural-sway measures, participants stood on the force plate for 30 s with eyes opened looking to a target. Based on the COP displacement, the ellipse area containing 95% of the COP data points (Area) was computed. The FMAX was measured during a countermovement jump. Specific handball actions composed the fatigue protocol in the format of a circuit with the gradual increment of laps. The force decreased ~9.5% after the fatigue protocol (p = 0.01) and returned to baseline values during the recovery phase at the fifth minute. For the postural sway, the Area decreased during the recovery phase until the fourth minute (p = 0.007). The fatigue protocol affected postural sway and force variables, which returned to baseline values after four minutes of the protocol. Therefore, we suggest that future fatigue analyses should be tested during this time window.
Listed In: Biomechanics, Posturography, Sports Science


Submaximal Normalizing Methods to Evaluate Load Sharing Changes in Repetitive Upper Extremity Work

The relationship between EMG and muscle force changes with muscle fatigue, making interpretation of load sharing between muscles over time challenging. The purpose of this investigation was to evaluate the efficacy of normalizing EMG data to repeated, static, submaximal exertions to mitigate the fatigue artifact in EMG amplitude. Participants completed simulated repetitive work tasks, in 60-second work cycles, until exhaustion and surface EMG was recorded from 11 muscles. Every 12 minutes, participants completed a series of 4 submaximal reference exertions. Reference exertion EMG data were used in 6 normalizing methods including 1 standard (normalized to initial reference exertion) and 5 novel methods: (i) Fatigue Only, (ii) Linear Model, (iii) Cubic Model, (iv) Points Forward, and (v) Points Forward/Backward. EMG data were normalized to each novel methods and results were compared to the Standard Method. The significant differences between the novel methods and the Standard Method were dependent on the muscle and the number of time points in the analysis. Correlation analysis showed that the predicted cubic model points correlated better to the actual data points than the linear predicted values. This novel method to create “fatigue debiased” ratios may better reflect the changing muscular loads during repetitive work. This method was evaluated with a novel data set examining the effects of repetitive shoulder exertions, in multiple axes, on load sharing in the shoulder over time. The normalizing method was effective at distinguishing between the effects of fatigue artifact on EMG amplitude and load sharing between muscles over time.
Listed In: Biomechanics


Prolonged Cycling's Effect on Transition Run Mechanics in Triathletes

A period of incoordination and fatigue is commonly associated with the transition run in triathletes, in which running mechanics are thought to be altered. Few studies have examined the changes in ground reaction forces and vertical loading rate during the transition run. Our purpose was to assess the changes that occur in ground reaction forces during a fatigued transition run in triathletes. 13 recreational male triathletes (34 ± 4.2 years) performed an incremental cycling test and a cycle to run transition on separate testing sessions. A 15-camera Vicon motion capture system collecting at 200 Hz and an AMTI force instrumented treadmill collecting at 2000 Hz were used in conjunction with a modified Plug-In Gait marker to collect trajectory and analog data for pre and post-cycling running trials. Ground reaction forces and temporal spatial parameters were assessed during stance of all running trials using Visual 3D software. Peak vertical ground reaction force and step length decreased significantly from pre-cycling to immediate post-cycling measures (p=.003, p<.001), no difference existed for either variable for pre-cycling vs. 10min post-cycling. Instantaneous peak vertical loading rate (IVLR) and step rate increased significantly from pre-cycling to immediate post-cycling measures (p=.05, p<.001), no difference existed for stride rate for pre-cycling vs. 10min post-cycling. IVLR remained significantly increased at the 10 min post-cyling (p=.035). The study findings suggest that fatigue from prolonged cycling can negatively impact triathletes’ ability to attenuate ground reaction forces in subsequent running.
Listed In: Biomechanics, Gait, Sports Science


Marathon Stride Rate Dynamics: A Case Study

The purpose of this study was to investigate stride rate (SR) dynamics of a recreational runner participating in his debut marathon. Tibial accelerometry data obtained during a half marathon (R1) and marathon (R2) were utilised. SR data were extracted utilising novel computational methods and descriptive statistics were utilised for analysis of R2, and comparison of the first half of the marathon (R2half) to R1. Results indicate that the participant employed comparable SR strategy in R1 and R2half. For R2 a combined decreasing trend in SR and increased variance in SR from 30 km (R2 =0.0238) was observed. Results indicate that the participant had the ability to maintain SR strategy for the first half of the marathon, however as fatigue onset occurred this ability decreased. Running strategies on SR during fatigue may be of future use to recreational runners.
Listed In: Biomechanics, Gait, Sports Science


Fatigue and Recovery in the Shoulder Complex While Performing Simulated Repetitive Work

The shoulder complex affords multiple opportunities for kinematic and muscular variability during repetitive work, which could change physical exposure and risk at work. The purpose of this study was to examine kinematic and muscular adaptations during continued performance of submaximal, repetitive work following a fatiguing protocol. Participants (n=12) completed a sequence of three protocols: (1) 20 pre-fatigue work cycles, (2) anterior deltoid fatigue protocol, (3) 60 post-fatigue work cycles. Each work cycle was 60 seconds and consisted of 4 tasks. Reaction forces and moments were recorded with a 6DOF force sensor (MC3-500, AMTI, Watertown, MA, USA) during the work tasks. The fatigue protocol consisted of static and dynamic efforts targeting the anterior deltoid. Fatigue was quantified through changes in strength, RPE and EMG frequency and amplitude. Activity of 14 muscles of the upper extremity and torso were measured with surface electrodes and kinematics were tracked with a passive motion capture system, 30 reflective markers and a scapular tracker. Immediately following the fatigue protocol, there were significant signs of muscle fatigue and reduced physical capacity. These changes were accompanied by significant muscular and kinematic adaptations in the work tasks during the post-fatigue work cycles (p<.05). Although these adaptations allowed for recovery in some muscles, fatigue persisted and developed in other muscles by the end of the post-fatigue work cycles, despite subjective ratings of perceived exertions returning to pre-fatigue levels. If people are unable to perceive negative behavioral changes during repetitive work, they may be at greater risk of developing workplace injuries.
Listed In: Biomechanics