Mental fatigue impairs physical performance in humans

FLzine
I just finished an interview with the fine folks at FLzine.com. I will give you all a heads up once the interview is posted. In it I discuss more mobility fun, why static stretching sucks, and much more.

Mental Fatigue Impairs Performance
Here is something that I have wondered about for years, but until recently never found any data.

When I started working in Technical Services for a major medical device company after my first 7.5 years in college many years ago in a galaxy far far away, I would get grilled all day answering calls from patients, reps, nurse and doctors. They ranged from Ethel that was too close to her microwave and she was trying to hide around the corner closing the door with a broomstick (microwaves and pacemakers are not an issue) to a physician at a device implant who is calling about a certain feature and you can hear the monitors in the background beeping.

I could not understand why I was so tired once I got home even though I sat no my butt all day! Part of this was from just not moving around much at all, but perhaps part of it was "mental fatigue"?

On to the Study
The nice part was the study below was a crossover design, so each subject acted as their own control. This allows you to use less subjects overall as you are only comparing 2 different conditions changes; so one with mental fatigue and the other without.

While it has been argued that a bike to exhaustion is not similar to a time trial format, the vast majority of evidence has been collected using that format. Time trials can be altered too by the subjects (esp. non competitive athletes) learning to pace themselves better.

The performance decrease did not appear to be from the heart/lungs (cardiorespiratory) or muscles! It appears to be all in your head indeed!

If anyone has watched lots of exercise tests to exhaustion will tell you, you need to be very careful what you say to them during a test. I always make it a point to explain everything up front and remind them that it is a max test. Once the test is over half way, I only use encouragement and do not give one group an "option" to quit. My guess is that if someone is working very hard (RPE of a 9 out of 10) and you reminded them that they can stop at any point now because the test is on a volunteer basis, many would just stop even though physically their numbers may be the same!

Other trials have attempted to get around this by giving money for the top performance to make it more competitive.

No mater how you cut it, endurance events at a high level are much about pain management.

Thoughts on the study? Let me know by posting a comment
Rock on
Mike T Nelson


Mental fatigue impairs physical performance in humans

Samuele M. Marcora, Walter Staiano, and Victoria Manning School of Sport, Health and Exercise Sciences, Bangor University, Bangor, Wales, United Kingdom Submitted 4 October 2008 ; accepted in final form 5 January 2009


Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated. In this randomized crossover study, 16 subjects cycled to exhaustion at 80% of their peak power output after 90 min of a demanding cognitive task (mental fatigue) or 90 min of watching emotionally neutral documentaries (control). After experimental treatment, a mood questionnaire revealed a state of mental fatigue (P = 0.005) that significantly reduced time to exhaustion (640 ± 316 s) compared with the control condition (754 ± 339 s) (P = 0.003).


This negative effect was not mediated by cardiorespiratory and musculoenergetic factors as physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. However, mentally fatigued subjects rated perception of effort during exercise to be significantly higher compared with the control condition (P = 0.007). As ratings of perceived exertion increased similarly over time in both conditions (P < style="font-weight: bold;">

CONCLUSION: In conclusion, our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms. Future research in this area should investigate the common neurocognitive resources shared by physical and mental activity.

Performance Research for August: Central Fatigue and testimonial

Testimonial time again.

I got to meet Franklin in person at his first RKC and then again at the RKC-FMS. Franklin also follows the Precision Nutrition lifestyle where I volunteer as a Community Moderator
Be sure to check out Franklin's blog HERE It is always a treat for me to interact and learn with great people such as him. Not sure how much credit I can take since I didn't lift any darn weights for him. Excellent work Franklin!

Mike,

First of all I need to first thank you kind words concerning my TSC results and secondly even more important for all the Z-Health advice you gave me over the few months. Without it, I would not have been able to perform at the level I did or even perform at all! As for my DL result, the 300 was a goal I set five months ago when 225 was my 1RM. I came pretty close and learned so much about this humbling lift that I can't wait to get started training it again!

Franklin, RKC

August Performance Research Update: Central Fatigue

Recovery from Supraspinal Fatigue is Slowed in Old Adults after Fatiguing Maximal Isometric Contractions.


Hunter SK, Todd G, Butler JE, Gandevia SC, Taylor JL. Exercise Science Program, Department of Physical Therapy, Marquette University, Milwaukee, Wisconsin, United States.

This study compared the contribution of supraspinal fatigue to muscle fatigue in old and young adults. Transcranial magnetic stimulation (TMS) of motor cortex was used to assess voluntary activation during maximal voluntary contractions (MVCs) of elbow flexor muscles in 17 young adults (25.5 +/- 3.6 yr; mean+/-SD) and 7 old adults (73.0 +/- 3.3 yr).

Subjects performed a fatigue task involving 6 sustained MVCs (22-s duration, separated by 10 s). Young adults exhibited greater reductions in maximal voluntary torque (67 +/- 15% of baseline) than the old (37 +/- 6%, P<0.001). p="0.02)." style="font-weight: bold;">

Conclusion: Recovery from the fatiguing exercise is impaired for old adults because of greater supraspinal fatigue than in the young.

My Notes: Some data here to show that as you age, your ability to recovery during training may become impaired. It should be emphasized that this was for max isometric contractions (holding a weight); so we are not sure if it would apply to a more standard contraction (where the weight moves).

Performance Research for July: Muscle Fatigue

Muscle Fatigue
I've always been interested as to why a muscle fatigues? Is there something going at the muscle level its self, or is it modified via the brain as a way for the body to protect itself? Most likely a combination of both, but here are some new studies that may help us untangle this mystery

MECHANISMS OF FATIGUE INDUCED BY ISOMETRIC CONTRACTIONS IN EXERCISING HUMANS AND IN MOUSE ISOLATED SINGLE MUSCLE FIBRES.

Place N, Bruton JD, Westerblad H. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.

Muscle fatigue (i.e. the decrease in muscle performance during exercise) has been studied extensively using a variety of experimental paradigms, from mouse to human, from single cell to whole-body exercise. Given the disparity of models used to characterize muscle fatigue, it can be difficult to establish whether the results of basic in vitro studies are applicable to exercise in humans.
In the present brief review, our attempt is to relate neuromuscular alterations caused by repeated or sustained isometric contraction in humans to changes in excitation-contraction (E-C) coupling observed in intact single muscle fibres, where force and the free myoplasmic [Ca(2+)] can be measured.
Accumulated data indicate that impairment of E-C coupling, most likely located within muscle fibres, accounts for the fatigue-induced decrease in maximal force in humans, whereas central (neural) fatigue is of greater importance for the inability to continue a sustained low-intensity contraction. Based on data from intact single muscle fibres, the fatigue-induced impairment in E-C coupling involves: (i) a reduced number of active cross-bridges owing to a decreased release of Ca(2+); (ii) a decreased sensitivity of the myofilaments to Ca(2+); and/or (iii) a reduced force produced by each active cross-bridge.

Conclusion: Data from single muscle fibre studies can be used to increase our understanding of fatigue mechanisms in some, but not all, types of human exercise. To further increase the understanding of fatigue mechanisms in humans, we propose future studies using in vitro stimulation patterns that are closer to the in vivo situation.

Acute norepinephrine reuptake inhibition decreases performance in normal and high ambient temperature.
Roelands B, Goekint M, Heyman E, Piacentini MF, Watson P, Hasegawa H, Buyse L, Pauwels F, De Schutter G, Meeusen R. Department of Human Physiology and Sports Medicine, Faculty of Physical Education and Physiotherapy, Vrije Universiteit Brussel, Brussels, Belgium.

Combined inhibition of dopamine (DA)/norepinephrine (NE) reuptake improves exercise performance and increases core temperature in the heat. A recent study demonstrated that this effect may primarily be related to increased DA activity. NE reuptake inhibition (NERI), however, has received little attention in humans, certainly in the heat, where central fatigue appears to be a main factor influencing performance. Therefore the present study examines the effect of NERI (reboxetine) on exercise capacity, thermoregulation, and hormonal response in normal and high temperature.

Nine healthy well-trained male cyclists participated in this study. Subjects ingested either placebo (Pla; 2 x 8 mg) or reboxetine (Rebox; 2 x 8 mg). Subjects exercised in temperate (18 degrees C) or warm (30 degrees C) conditions and cycled for 60 min at 55% W(max) immediately followed by a time trial (TT; Pla18/Rebox18; Pla30/Rebox30) to measure exercise performance. Acute NERI decreased power output and consequently exercise performance in temperate (P = 0.018) and warm (P = 0.007) conditions. Resting heart rate was significantly elevated by NERI (18 degrees C: P = 0.02; 30 degrees C: P = 0.018). In Rebox18, heart rate was significantly higher than in the Pla18, while in the heat no effect of the drug treatment was reported during exercise. In Rebox30, all hormone concentrations increased during exercise, except for growth hormone (GH), which was significantly lower during exercise. In Rebox18, prolactin (PRL) concentrations were significantly elevated; GH was significantly higher at rest, but significantly lower during exercise.

Conclusion: Manipulation of the NE system decreases performance and modifies hormone concentrations, thereby indicating a central NE effect of the drug. These findings confirm results from previous studies that predominantly increased DA activity is important in improving performance.

Neuromuscular fatigue following constant versus variable-intensity endurance cycling in triathletes.

Lepers R, Theurel J, Hausswirth C, Bernard T. University of Burgundy, Faculty of Sport Sciences, France. romuald.lepers@u-bourgogne.fr

The aim of this study was to determine whether or not variable power cycling produced greater neuromuscular fatigue of knee extensor muscles than constant power cycling at the same mean power output. Eight male triathletes (age: 33+/-5 years, mass: 74+/-4 kg, VO2max: 62+/-5 mL kg(-1) min(-1), maximal aerobic power: 392+/-17 W) performed two 30 min trials on a cycle ergometer in a random order. Cycling exercise was performed either at a constant power output (CP) corresponding to 75% of the maximal aerobic power (MAP) or a variable power output (VP) with alternating +/-15%, +/-5%, and +/-10% of 75% MAP approximately every 5 min. Maximal voluntary contraction (MVC) torque, maximal voluntary activation level and excitation-contraction coupling process of knee extensor muscles were evaluated before and immediately after the exercise using the technique of electrically evoked contractions (single and paired stimulations). Oxygen uptake, ventilation and heart rate were also measured at regular intervals during the exercise. Averaged metabolic variables were not significantly different between the two conditions. Similarly, reductions in MVC torque (approximately -11%, P<0.05)>0.05) between CP and VP trials. The magnitude of central and peripheral fatigue was also similar at the end of the two cycling exercises.

Conclusion: Following 30 min of endurance cycling, semi-elite triathletes experienced no additional neuromuscular fatigue by varying power (from +/-5% to 15%) compared with a protocol that involved a constant power.

Differential effects of endurance and resistance training on central fatigue.

Triscott S, Gordon J, Kuppuswamy A, King N, Davey N, Ellaway P. Department of Clinical Neuroscience, Imperial College London, London, UK.

The effect of long-term endurance and resistance training on central fatigue has been studied using transcranial magnetic stimulation by exercising the biceps brachii to exhaustion and recording motor-evoked potentials from the non-exercised homologous biceps. Three groups of eight healthy individuals took part: two groups of individuals who had more than 8 years of athletic training in either an endurance or resistance sport, and a group of controls. The size of a motor-evoked potential (area of averaged rectified response) was significantly depressed in all three groups in the non-exercised arm after exhaustive exercise of the opposite arm. Recovery of motor-evoked potentials occurred earlier in endurance athletes (20 min) than in control participants (30 min) and resistance athletes (>30 min). Dexterity and maximum voluntary contraction of the biceps for the non-exercised arm were not depressed in any group.

In a separate session, the limit of endurance time for the biceps was reduced significantly following exhaustive exercise of the biceps of the other arm for resistance athletes and control participants, whereas there was no change in the endurance athletes.

Conclusion: Athletic training has an effect on the mechanism of central fatigue that may be specific to the nature of training.

My Notes: The SAID principle once again!