Running Head: REACTION TIME AND FATIGUE Effects of Fatigue on Reaction Time California Polytechnic State University Kelly Adams, Jourdan Muro, Benjamin Stanely, Ivy Tseng 1 REACTION TIME AND FATIGUE 2 Reaction Time and Fatigue Physical performance is essential to almost every sport, whether it be in football, basketball, dance, rock climbing or pole vaulting. People generally want to perform well so that they may excel in their sport, but many sports require long bouts of muscular endurance that can lead to muscular fatigue. Fatigue is something that has been known to play a big role in limiting performance; so when people tire out, how can they continue to perform at the same level they were? Muscle fatigue is defined as the decline in the ability of a muscle to generate force. When a muscle becomes tired, the ability of the muscle fiber to contract is reduced and the nerve’s ability to generate a signal becomes limited. Much of this can happen as a result of vigorous exercise. Prior to conducting our own tests, we examined several articles researching the effects that fatigue may have on performance. An article on the effect of lower extremity muscular fatigue on motor control performance aimed to determine whether lower extremity fatigue affects the ability of an individual to balance on an unstable platform (Howard, Cawley & Losse, 1998). Another study examined the effects of fatigue on the kinematics of free-throw shooting (Uygur, Göktepe, Ak, Karabörk & Feza Korkusuz, 2010). Other researchers studied the effects of an intermittent exercise fatigue protocol on the biomechanics of soccer kick performance (Kellis, Katis & Vrabas, 2006). Smilios studied the effects of varying levels of muscular fatigue on vertical jump performance (Smilios, 1998). The results all indicated that there was a connection between fatigue and performance. The purpose of our study was to determine if fatigue has an effect on reaction time in the transverse flexors and the flexors of the digits. From our own understanding and the research we did prior to conducting out tests, we hypothesized that muscular fatigue would have a negative effect on reaction time. REACTION TIME AND FATIGUE 3 Eighteen Cal Poly students in the KINE 319-02 class participated in the study, consisting of nine male and nine female participants. Inclusion criteria required that participants were Cal Poly kinesiology students between the ages of 19 and 23. The exclusion criteria required that participants had no current or recent injuries and were not absent during either day the testing was conducted. Testing began with attaining baseline reaction times for all participants in both the pinch-grip reaction test and clap reaction test. For the pinch-grip ruler-drop test, participants were instructed to hold their dominant hands out in front of them with their fingers four inches apart. A foot long ruler was held in the middle of their “claw-shaped” hand, directly above the index finger. The tester then dropped the ruler without warning and the subject had to react and pinch their fingers to their thumb to catch the ruler, activating the flexors of the digits. Wherever the fingers ended up on the ruler after catching was distance recorded. During the clap ruler-drop test, participants were instructed to hold their arms out in front of them, perpendicular to their body, with their hands four inches apart. The foot-long ruler was held directly over their index finger. When the ruler was randomly dropped by the tester, the participants were instructed to clap their hands together in order to catch the ruler, activating the transverse flexors. After obtaining baseline data from all participants, each subject was randomly assigned to either complete the dead-hang or half-pushup hold to failure. The dead-hang would fatigue the flexors of the digits while the half-pushup hold would fatigue the transverse flexors. After completing either the dead hang or half push-up fatigue protocol until perceived failure, the participants immediately completed either the pinch-grip or clap ruler-drop test, respectively. REACTION TIME AND FATIGUE Table 1 Total # Participants 18 (9 male, 9 female) Age (years) 19-23 Height (cm) 172.56 ± 10.435 Weight (kg) 70.3 ± 12.716 Our study included 18 participants including 9 males and 9 females between the ages of 19-23. The average height of our participants was 172.56cm ± 10.435cm and the average weight was 70.3cm ± 12.716cm. 4 REACTION TIME AND FATIGUE 5 In order to analyze our collected data, we ran two dependent t-tests using JMP software. One compared the pinch grip ruler test at baseline, to the same test post-dead-hang. The second compared the clap ruler test at baseline and post-half-pushup hold. These t-tests allowed us to see if there was a difference between the two conditions at baseline and following fatigue. Table 2: The Post-dead-hang reaction time was .56cm better than the baseline reaction time. However, the p-value was .74 which was far greater than our alpha level which we set at 0.05. This indicates that the difference between the two groups was non-significant. REACTION TIME AND FATIGUE The post-pushup hold reaction time was .25cm better than the baseline reaction time. However, the p-value is .89. This indicates that the difference between groups is nonsignificant. Based on our statistical analysis we found that both the half push-up and dead hang to fatigue resulted in faster reaction times, however, these improvements were not statistically significant. 6 REACTION TIME AND FATIGUE 7 After analyzing the results, we came to the conclusion that our hypothesis was not supported. Our hypothesis stated that both muscle groups would have a slower reaction time after the fatigue protocol, but there was no statistically significant data to support our claim. The data was very scattered: some participants performed better after the fatiguing and some performed worse. We also hypothesized that the pectoralis major would have a faster reaction time than the wrist flexors, but the data showed slower reaction times overall in the wrist flexors pre/post fatigue than in the transverse flexors pre/post fatigue. One of the main strengths of our study was that we tested two different functional muscle groups of various sizes located at different distances from the central nervous system. Most of the studies done on fatigue and reaction time have focussed around one specific muscle group without comparing how reaction time might be affected differently during fatigue based on muscle size, type and distance from the central nervous system. Another strength of our study was that it was a between-subjects randomized cross-over study, so each participant performed both tests pre and post fatigue protocols and the randomization of the groups lowered the possibility of confounding variables between the two groups. The study also consisted only of Kine 319 lab students at Cal Poly so there is high internal validity for Cal Poly Kinesiology majors. There were a few limitations to this study. The first was that, our subject group was limited to Kine 319 lab students at Cal Poly. This meant there would be little external validity when applying our results to the general population. Another limitation was testing and instrumental error. The study was not blinded to the researcher recording the data and could have had a bias towards our hypothesis that may have affected the results that were recorded. The REACTION TIME AND FATIGUE 8 main weakness of this study, however, is the poor execution of the protocols we set in place. Our hypothesis was rejected based on our data because we found muscular fatigue to have no statistically significant effect on reaction time. After doing more research, we found that Sant' Ana and colleagues conducted a study on Taekwondo kicks and the impact it has on reaction time. They determined that muscular fatigue to negatively impacts reaction time (Sant’Ana et al,. 2017). The likeliest cause of our inconsistent data was due to the fact that most participants did not perform their fatigue protocol to failure as instructed. Many of the participants said they had gone to failure, but displayed signs of energy and lack of muscular fatigue. Other participants were more honest about their perceived exertion, but still ended before muscle failure or even fatigue because they were not having fun or were planning to exercise later and didn’t want to pre-fatigue themselves. Despite the reasons, many of the participants were not receiving proper muscular fatigue during the exercise and, rather than exhausting the muscle, these participants might have done just enough to stimulate the muscle and quicken neural activation, leading to a quicker reaction time on the post fatigue test. Future research comparing the effects of fatigue on the reaction time of various muscle groups, testing neural activation of skeletal muscle when performing a fatigue protocol would be something worth conducting next. The researcher should also ask for a rate of perceived exertion after the fatiguing exercise has been completed, so if the data does seem off one can look back at the RPE and see if that was a possible cause. Providing the participants with some type of incentive might also cause more energy exertion during the fatiguing period and lead to less threat to validity. REACTION TIME AND FATIGUE 9 References Howard, M. E., Cawley, P. W., & Losse, G. M. (1998). Effect of lower extremity muscular fatigue on motor control performance. Medicine and science in sports and exercise, 30(12), 1703-1707. Kellis, E., Katis, A., & Vrabas, I. S. (2006). Effects of an intermittent exercise fatigue protocol on biomechanics of soccer kick performance. Scandinavian journal of medicine & science in sports, 16(5), 334-344. Sant’Ana, J., Franchini, E., da Silva, V., & Diefenthaeler, F. (2017). Effect of fatigue on reaction time, response time, performance time, and kick impact in taekwondo roundhouse kick. Sports biomechanics, 16(2), 201-209. Smilios, I. (1998). Effects of varying levels of muscular fatigue on vertical jump performance. Journal of Strength and Conditioning Research, 12, 204-208. Uygur, M., Goktepe, A., Ak, E., Karabörk, H., & Korkusuz, F. (2010). The effect of fatigue on the kinematics of free throw shooting in basketball. Journal of human kinetics, 24, 51-56.
