Review on Resistance Training and Average Motor Unit Firing Rates

Review on Resistance Training and Average Motor Unit Firing Rates

            In 2011, Beck et al. conducted a study looking at the average motor unit firing rates of untrained men after an 8-week strength program. Their findings, done by electromyography (EMG) measurements, found that the program had no effect on average motor unit firing rates and their relationship to the recruitment threshold. In order to better understand this study, some key terms will be defined. Along with the definitions, some suggestions will be made as to why untrained subjects may not have been the optimal participants, as well as some possible changes. Finally, the actual mechanisms of strength gain during this 8-week program will be opined and looked into.

Discussion

            Some key terms must be defined in order to help the reader better understand the article itself and this article review. The first is the vastus lateralis, which is the lateral portion of the quadriceps muscle. The next is electromyography, referred to henceforth as EMG. EMG is the measure of the muscle’s amplitude of contraction measured in electrical signals. This is referred to by Beck et al. (2011) as a combination of “the number of active motor units and their firing rates” (p. 1). Personally, I have worked with this concept as a neurological intra-operative monitoring technician. During lumbar spinal fusions, needle electrodes were place in the vastus lateralis muscle any time a surgeon was working in the vicinity of the L2 to L5 motor nerve root area. By reading EMG signals, the technician is able to give the surgeon feedback is the motor nerve root is touched or irritated by responses in the muscle. This was also accentuated by heavy EMG activity matching up to being able to see the patient physically move on the table. The most important aspect of this was the surgeon placing pedicle screws into the vertebral column. By placing an electrode on the screw and stimulating it, the surgeon was able to see a threshold voltage required to elicit a muscular EMG response. The lower the threshold, the closer the screw was to the motor nerve root. Powers and Howley (2012) define the motor unit as a “motor neuron and all the muscle fibers that it innervates” (p. 153). The term motor unit firing rate refers to the rate at which the motor unit is able to conduct action potentials to the muscle. High and low threshold motor units can be defined simultaneously, once again referring to the 2012 text by Powers and Howley. The threshold refers to the point at which a stimulus to the motor neuron reaches a sufficient strength and enough sodium has diffused into the cell. Once it reaches a critical “threshold” level, the all or none action potential begins. For lower threshold motor units, it refers to a lower level of stimulus and sodium diffusing into the cell; whereas high threshold motor units refer to a higher level of stimulus needed to cause the action potential. This goes hand-in-hand with a term called the size principle, which will be explored at a later section of this paper. Isometric contraction refers to a contraction that is held in place, the muscle is neither shortening, as in concentric contraction, or lengthening, as in eccentric contraction (Powers & Howley, 2012). The term “80% max voluntary contraction rate” refers to the participant contracting their muscle voluntarily at about 80% of their maximum contraction.
            The study by Beck et al. (2011) used eleven untrained men, which may not have been optimal due to delayed onset muscle soreness (DOMS). The participants in the study had not done any weight training in the six months prior to the study. Unsurprisingly, the first few weeks of the study saw a decrease in the maximum force, measured in Newtons, that the subjects were able to produce (Figure 4). The decrease in force could be due to DOMS, which is typical for novice weightlifters (Powers & Howley, 2012). DOMS usually manifests within 24 to 48 hours after training, and can be caused by a number of steps in the process. The steps are outlined by Powers and Howley (2012). It usually involves structural damage to the fibers, membrane damage, calcium leaking out of the sarcoplasmic reticulum, breakdown of cellular proteins, inflammatory response, and finally edema and pain (p. 492, Figure 21.4). Trained subjects would have been less likely to exhibit a DOMS response, and may have resulted in a better look at motor unit firing rates and recruitment threshold without the initial decreases in force production seen in the untrained subjects. For future studies with regard to subjects alone, it would be interesting to conduct the same study with an untrained group and an untrained group. With this, one could see the changes in both, as well as any differences in force production throughout the study, average motor unit firing rates, and the relationship to recruitment threshold.
            It is opined that there are two primary principles for strength increases. The first is the size principle, mentioned about. The size principle is the body’s recruitment of more and more motor neurons as force production needs increase (Powers & Howley, 2012). This is also linked to the subject better learning the movement pattern, allowing the motor units to synchronize better, and may also remove some of the motor unit inhibitions (Powers & Howley, 2012). The other adaptation that results in strength increases is muscular hypertrophy. Physiologically, the more myosin cross-bridges that are available to attach to actin, the more force is able to be produced (Powers & Howley, 2012). Larger muscles would obviously contain more actin and myosin, and thus be able to produce more force.

Conclusion

            The article by Beck et al. (2011) shows an interesting look at strength training adaptations in untrained subjects. It is a study that makes sense in the broad overview of strength and conditioning physiology, and opens up numerous future studies of interest.

References

Beck, T. W., DeFreitas, J. M., & Stock, M. S. (2011). The effects of a resistance training
            program on average motor unit firing rates. Clinical Kinesiology, 65(1), 1-8.
            Retrieved from http://www.delsys.com/decomp/2011_Beck_et_al.pdf

Powers, S. K., & Howley, E. T. (2012). Exercise physiology: Theory and application to fitness
            and performance. New York, NY: McGraw-Hill.

Training Mistakes and Effects on Performance in Nutrition and American Football

Abstract

This paper explores common training mistakes that I have personally seen or am aware of through anecdotal evidence. The paper will focus on mistakes in the realm of nutrition in regards to weight control. Fad diets such as the Atkins Diet, Mediterranean Diet, or Ketogenic Diet, seem to be quick fix diets to improve body composition; however, effective diets are as the result of lifestyle changes, not quick fixes. Sacks et al. found in their research that caloric restriction favorably affects body weight, regardless of what kind of macronutrient composition one may choose (2009). Another common training mistake, this time in the realm of American football, comes from the players doing too much aerobic work. Football is a game based on speed and power. Hennessy and Watson found that groups doing endurance work along with their strength work resulted in interference to power and speed (1994). This paper will examine these common mistakes, as well as alternative future research.

Training Mistakes and Effects on Performance in Nutrition and American Football

            Numerous studies have been done in the realm of nutrition, as well in the realm of training for strength and power. Regardless of the amount of studies, there are still some basic mistakes being made in regards to nutrition for weight loss and strength and power for the American football player. In a combination of both principles, Torres-McGehee et al. found that while athletic trainers and strength and conditioning coaches showed knowledge of nutritional principles for their sport, coaches and athletes did not (2012). While some fad diets such as the Mediterranean and a low-carb approach had shown better results, studied by Shai et al. in 2008, Sacks et al. found that weight loss was generally the same based on caloric restriction (2009). Powers and Howley also pointed out that calories count in any weight loss regimen (2012). This could lead one to the logical conclusion that, based on available evidence, lifestyle changes would be more important and more sustainable over the long-term for weight control. A fad diet or a temporary fix may show favorable results, but may not be as sustainable as long-term changes. Also of note, Fothergill et al. found contestants of The Biggest Loser, who had gone through drastic diet and exercise changes for a quick fix, had significantly lessened their metabolic rate. This only adds to the belief that long term changes are the answer.
            American football is a game of power and speed. There still seems to be a prevailing belief that a player needs to have aerobic work built in to the training program. Burgomaster et al. found that conducting high intensity interval training had comparable results to traditional endurance training (2008). This could lead one to believe that the player would get similar results from endurance training, with a less significant time commitment. Moreover, Hennessy and Watson found that adding endurance training into a strength program compromised lower body strength gains and showed no improvement in speed and power. Elliott, Wagner, and Chiu also reported that aerobic training, such as distance running, could compromise performance for power and speed athletes (2007). Power and Howley also point out “that strength development is impaired during concurrent training”, concurrent training meant to be combining strength and endurance training (2012). This could reasonably lead to the conclusion that endurance training is unnecessary for the development of a football player, and may even be detrimental to the key attributes that make a football player successful.

Literature Review

            Krieger, Sitren, Daniels, and Langkamp-Henken found in a 2006 study that low-carbohydrate, high-protein diets had a favorable effect on body mass and composition. They reviewed various studies of different diets and found that this type of diet did have a more favorable effect. These studies were done in the short term, and would be interesting to see if a long-term study had the continued favorable effects compared to caloric restriction alone.
            Shai et al., in a 2-year study, also found that low-carbohydrate and Mediterranean diets could be effective alternatives to the usual low-fat diet (2008). This is helpful in that it may help someone tailor a diet to their own tastes and still maintain a healthy weight or weight loss, goal-dependent.
            Sacks et al., also in a 2-year study, found that any type of caloric restriction would result in meaningful weight loss (2009). The participants in this study were assigned into four different diet groups with four different types of macronutrient percentages. They found that all diets resulted in weight loss and satisfaction with the diet was associated with continued weight loss, found to be roughly 0.2 kg of body weight loss per session. This, along with Shai et al., could help with the argument that nutrition is more about lifestyle changes than a quick fix diet.
            Fothergill et al. did a study on contestants of the television show The Biggest Loser six years after they had competed on the show (2016). The results of their study found persistent metabolic adaptations, even six years later, persisted well below baseline. This even more strongly suggests that a long-term lifestyle change is needed. Contestants on a show like this, with extreme changes to diet and exercise, could generally be outliers in the normal population of overweight adults attempting to lose weight; most adults don’t have the time to dedicate primarily to nutrition and exercise as a contestant in a reality show would. This could also make the case that long-term weight loss would be better accomplished by a slower approach, as perhaps the metabolic adaptations would not be as severe.
            Finally, shifting over to sports performance, Torres-McGehee et al. found that coaches and players lacked nutritional information to help with performance. It was found that athletic trainers and strength and conditioning specialists had adequate knowledge, whereas coaches and players did not. One part of the questionnaire that was answered involved weight management, which could realistically show that the coaches and players are unprepared nutritionally to not only reach peak performance, but to eat properly for a favorable body weight in regards to the athletic event.
            Hennessy and Watson conducted a study using four groups: an endurance training only group, a strength and endurance training group, and a strength only group (1994). While the endurance group, as well as the strength and endurance group showed gains in endurance, these groups also showed no gains in power or speed, two critical components to football. The strength group showed improvements in strength and power, and also maintained endurance.
            Elliott et al., in their 2007 study, noted that endurance exercise, such as running, was detrimental to performance for power athletes. They proposed that this could be a result of “inappropriate neuromuscular adaptation”, catabolic hormones, or just simply overtraining. This is echoed in Powers and Howley’s 2012 text focusing on possible compromises in strength as a result of using concurrent strength and endurance training.
            Finally, Burgomaster et al. found similar adaptations from high intensity interval training compared to endurance training (2008). This study did not focus on any possible compromises in strength, speed, or power, but primarily focused on muscular and metabolic adaptations.

Discussion

            In regards to weight management, there is little doubt that manipulating macronutrients is an effective strategy. Krieger et al. and Shai et al. both reported similar findings that low-carbohydrate diets had a favorable effect on body composition and weight (2006 and 2008, respectively). It is the 2009 Sacks et al. study that supports meaningful weight loss being a lifestyle change. The findings of that study that any type of caloric restriction would result in weight loss would point out that going to a fad diet could possibly be a mistake for an overweight adult attempting to lose weight. Losing weight and keeping it off is a long-term goal. Fothergill et al. showed as much in their 2016 study. This is not something that is an overnight, immediate quick fix. Approaching nutrition as such would run the risk of long-term metabolic compromise such as Fothergill et al. noted (2016). It should be noted that this is not to say that a Mediterranean or low-carb diet are unrealistic. Shai et al. showed that they are effective, and if it preferable to an adult to use those types of diets then there is no reason they shouldn’t (2008). The more important part of this is the long-term change. Sacks et al. noted that 80% of participants completed the trial, and attendance and motivation was highest for those who were showing continual weight loss (2009). So to say to avoid any type of diet such as these would be inaccurate. If anything, it paints the picture that it is a preference of the adult attempting to lose weight. It would be pertinent to point out, however, that it is not a quick process. That is where a majority of mistakes are made. The studies done by both Shai et al. and Sacks et al. were of a 2-year duration. To not only lose weight, but to keep the weight off, is a long-term commitment. It can be assumed that it is a mistake for someone to look to a fad diet as a quick fix in lieu of a lifestyle change for the better. Also in the realm of athletes, better nutritional knowledge would help avoid an athlete or a coach recommending any type of quick fix. Torres-McGehee et al. showed the information gap between athletic trainers and coaches/athletes; closing this gap by increasing knowledge would help to not only improve athletic performance, but to set an athlete up for a lifelong commitment to healthy nutritional habits (2012).
            Hennessy and Watson (1994), Elliott et al. (2007), and Powers and Howley (2012) all seem to be in agreement that endurance training will at best result in no improvements in speed and power, and at worst compromise strength, speed, and power. Elliott et al. point out that some of the mechanisms for this would include improper neuromuscular adaptations, catabolic hormones, and an increased risk of overtraining (2007). Powers and Howley go into detail with possible causes (2012). Neural factors are one suggested mechanism, as the concurrent training could impair recruitment and result in decreased force production. Though, Powers and Howley do note that limited evidence exists to support this conclusion (2012). They also point out that low muscle glycogen content could be a factor. Successive bouts of either resistance or endurance training could result in low muscle glycogen content, impairing performance, especially in the realm of strength training (2012). This would also be a factor ruling against an athlete using any kind of low carbohydrate diet for the sake of weight management; it could be argued that this would further compromise performance. Powers and Howley also suggest that overtraining could be a factor that impedes strength; though, again, it is noted that there are no studies that prove this (2012). The shift from fast fiber type to slow fiber type from endurance training would also be a contributing factor that would negatively affect speed and power, especially in a shift away from Type IIx fiber types (Powers & Howley, 2012).
            As anecdotal evidence, there still seems to be a prevailing attitude that endurance training is a key testing milestone for football players when they report to pre-season camp. The more common ones that were seen throughout my time as a coach were either 16 repetitions of 100-meter sprints with minimal rest, or 6 repetitions of 300 meter sprints with minimal rest. Though this doesn’t necessarily test out how fast, strong, or powerful an athlete is, it still seems to be a staple of collegiate football programs. Burgomaster et al. provides a good solution to this in their 2008 study. It is pointed out that high intensity interval training would result in the same type of adaptations as types of endurance training. With that in mind, if a coach insists on using conditioning tests, high intensity interval training would be a good middle ground to use. It should be noted that Burgomaster et al. did not study high intensity interval training effects on speed and power; this study is primarily to show that there is a middle ground to lessen the time commitment of athletes while achieving the same desired results as endurance training (2008).

Limitations of These Studies

            Physiological Limitations. It should be noted that a limitation, especially in regards to the studies done on diet, would be physiological limitations. The amount of variability from person to person is tremendous; it would almost be impossible to completely eliminate those limitations. Genetically, there will always be those differences. Some adults may better be able to utilize free fatty acids as a fuel; likewise, some may be able to rely more on carbohydrates as a fuel without any type of insulin resistance. Some folks may put on muscle mass more easily, while others may put on fat more easily. It would be impossible to tell all of those for certain. Likewise, some athletes with a higher amount of Type IIx fibers may benefit more from high intensity interval training in regards to general conditioning to help avoid fatigue during game situations.

Conclusions and Future Studies

            In conclusion, Sacks et al. showed that an important factor of weight loss is plainly caloric restriction (2009). Though the other studies showed that low-carbohydrate or Mediterranean diets were effective in weight reduction, one must wonder if those are sustainable changes for life. Proposed future studies could be an explanatory sequential mixed methods study in which weight loss data is gathered followed by qualitative data gathered to measure the participant’s sense of well-being throughout the study. One could also do an exploratory sequential mixed method design to get a sense of the participant’s feeling of well-being throughout the study to see if there is any correlation between the qualitative data of well-being and the quantitative data of weight.
            In regards to common training mistakes for football players, it is plain to see from numerous studies that concurrent training would at best result in no improvements to power and speed, or at worst compromise strength, power, and speed. Burgomaster et al. gave a viable alternative to a possible coaching preference to test conditioning by using high intensity interval training in lieu of endurance training. Future studies could include exploratory sequential mixed methods study in regards to testing. The athlete could fill out a questionnaire for the researcher to get a sense of the athlete’s feeling of well-being before they complete all of usual preseason tests, such as bench press, 40-yard dash, pro shuttle, and vertical jump. This would be accomplished once before summer training starts, and once before preseason practices starts, usually over the course of a 12-week training cycle. As Powers and Howley note in their 2012 text, arousal and motivation are factors that affect athletic performance. It would be interesting to see if the athlete’s sense of well-being had any correlation with athletic performance.
            Regardless, as knowledge and application of nutritional and football performance principles increase, so can we expect to see better improvements in technology and information to help people attain their goals, whatever they may be.

References

Burgomaster, K. A., Howarth, K. R., Phillips, S. M., Rakobowchuk, M., MacDonald, M. J.,
            McGee, S. L., & Gibala, M. J. (2008). Similar metabolic adaptations during exercise after            low volume sprint interval and traditional endurance training in humans. Journal of
            Physiology, 586(1), 151-160. doi:10.1113/jphysiol.2007.142109.

Elliott, M. C., Wagner, P. P., & Chiu, L. (2007). Power Athletes and Distance Training. Sports
            Medicine, 37(1), 47-57. doi:10.2165/00007256-200737010-00004.

Fothergill, E., Guo, J., Howard, L., Kerns, J. C., Knuth, N. D., Brychta, R., … Hall, K. D.
            (2016). Persistent Metabolic Adaptation 6 Years After “The Biggest Loser” Competition.
            Obesity Journal, 00(00), 1-8. doi:10.1002/oby.21538.

Hennessy, L. C., & Watson, A. W. (1994). The Interference Effects of Training for Strength and Endurance Simultaneously. The Journal of Strength and Conditioning Research, 8(1).
            Retrieved from http://journals.lww.com/nsca-            jscr/Abstract/1994/02000/The_Interference_Effects_of_Training_for_Strength.3.aspx.

Krieger, J. W., Sitren, H. S., Daniels, M. J., & Langkamp-Henken, B. (2006). Effects of variation            in protein and carbohydrate intake on body mass and composition during energy       restriction: a meta-regression. The American Journal of Clinical Nutrition, 83(2), 260-            274. Retrieved from http://ajcn.nutrition.org/content/83/2/260.short.

Powers, S. K., & Howley, E. T. (2012). Exercise Physiology: Theory and Application to Fitness
            and Performance. New York, NY: McGraw-Hill.

Sacks, F. M., Bray, G. A., Carey, V. J., Smith, S. R., Ryan, D. H., Anton, S. D., … Williamson,
            D. A. (2009). Comparison of Weight-Loss Diets with Different Compositions of Fat,        Protein, and Carbohydrates. The New England Journal of Medicine, 360(9), 859-873.
            doi:10.1056/NEJMoa0804748.

Shai, I., Schwarzfuchs, D., Henkin, Y., Shahar, D. R., Witkow, S., Greenberg, I., … Stampfer,
            M. J. (2008). Weight Loss with a Low-Carbohydrate, Mediterranean, or Low-Fat Diet.
            The New England Journal of Medicine, 359(3), 229-241. doi:10.1056/NEJMoa0708681.

Torres-McGehee, T. M., Pritchett, K. L., Zippel, D., Minton, D. M., Cellamare, A., & Sibilia, M.
            (2012). Sports Nutrition Knowledge Among Collegiate Athletes, Coaches, Athletic           Trainers, and Strength and Conditioning Specialists. Journal of Athletic Training, 47(2),
            205-211. Retrieved from http://www.natajournals.org/doi/abs/10.4085/1062-6050-            47.2.205.

Jon

I apologize ahead of time if this seems extremely disjointed and kind of all over the place. I've been writing this on my phone and working on it over the course of a few days, so my apologies in advance if it seems incoherent and rambling.

When I was growing up, there were few people I looked up to more than my older cousins Eric, Jon, Kate, and Dan. They lived about ten minutes away and were definitely an integral part of my life. Being able to spend time with any of them was always the highlight of my day, no matter what the day had brought.

Tuesday morning I got the news that Jon had died at the age of 38. I think that was the biggest shocker I've had in years. I've spent some time trying to put together the words to describe my wonderful cousin and what he meant to all of us, and I still feel that they'll be woefully inadequate to describe such an amazing, special human being.

Jon was always really laid back and relaxed. I think he was the only babysitter I wasn't a complete unholy terror to (sorry to you other 3). Jon definitely lived his life to the fullest, on his terms. I rarely saw him upset, and could always enjoy my time with him. He was easy to open up to, outgoing, and a great friend. I remember the night before Kate's wedding, the two of us hung out, having some whiskey and just talking until almost 4 in the morning. We definitely paid dearly for it the next day, but it was worth it and I wouldn't trade that time in for anything.

Most of all, I will remember just how much Jon cared. The last time I really got to spend time with him was Dan's wedding. He was still laid back, and still a blast just to be around. He was always positive when I was around him, and I'll miss that about him dearly.

I can't imagine the pain my cousins and my Aunt and Uncle are going through right now, I just wish they didn't have to feel it.

Jon - I love you very, very much. You were a great cousin and friend, and I will miss you dearly. No one's ever really gone as long as you remember them, and I can promise I'll never forget the good times we had together. I love you.

PS - I'll be sure to keep reminding Dan he worked for the Navy every time I see him