Sports science often gets bad press, and I’m not entirely sure why. Recently, Wayne Goldsmith published an article titled “Sports Science: You’ve Still Got it Wrong,” in which he detailed 10 points where he felt sports science was failing. While there were many problems with the article—including the fact that he appeared to be conflating people who do sports science (i.e., sports scientists) with the discipline of sports science—it’s always important to try and take criticisms of your field seriously, especially when they come from the people you want to help: athletes and coaches.Sports science research can do better in some areas to help athletes & coaches improve performance. Click To Tweet
Though there were some good rebuttals of the original article, including this from Queensland University of Technology senior lecturer Vince Kelly, the article got me thinking about areas in which sports science research could do better in order to assist athletes and coaches in their quest to enhance performance. In this three-part series, I explore 10 different research questions for which I feel sports science could make a big difference by attempting to answer—and in many cases, is close to doing so. Obviously, I have my own biases, and some of these questions are for the fields in which I hold a strong interest, but I have tried to cast the net as wide as possible. For each question, I’ve provided:
- A brief review of what we know so far.
- Why it’s important to know more.
My expectation is that, over the next 10 years, we will get closer to more concrete answers in many of these.
Is a Low-Carb, High-Fat Diet Effective for Athletes?
Though it is often easy to forget, athletes are normal people too, which means that the internet—especially social media—is a major source of information for them. Athletes are always looking for ways to gain an edge over their competitors, and they tend to focus on nutrition because this is often something directly under their control (as opposed to coach-directed training). Plus, they consume food multiple times per day (as opposed to training, which often happens just once or twice per day). Consequently, research demonstrates that athletes are increasingly susceptible to diet fads, something that I can attest to on a personal level, having followed various different diets—including paleo and keto—during my athletic career.Athletes looking for an edge tend to focus on nutrition because it’s something they can control. Click To Tweet
Recently, we’ve seen a rise in “biohacking,” in which both the ketogenic diet and fasting are very popular. Furthermore, many of these biohackers, such as Tim Ferriss and Ben Greenfield, have maneuvered into the athletic performance realm, making athletes even more likely to discover their work. Additionally, Tim Noakes, an acclaimed sports scientist responsible for a number of important breakthroughs within the field, has also fully endorsed a ketogenic-esque diet. Ketogenic diets typically require individuals to consume less than 20 grams of carbohydrates per day, which is the equivalent of around 30g of oatmeal. A slightly more relaxed version of the ketogenic diet, which is the type more commonly promoted, is the Low Carb, High Fat (LCHF) diet, which tends to be a bit less strict on the upper thresholds of carbohydrate intake, but still requires significant carbohydrate restriction.
A Bit of Theory
During prolonged, lower-intensity exercise (around about 65% or less of VO2max), the body can utilize fat as its main source of energy. This is a good thing, because even a very lean individual has extensive fat stores on their body; more than enough to see them through a marathon or ultra-endurance event. If you consume an LCHF diet, then your body becomes more efficient at utilizing fats at these lower intensities, and potentially even a bit more at higher intensities. This means that (in theory) you could:
- Exercise for longer; and
- Do so without having to consume additional energy (i.e., eat or drink) during a competition, which could reduce feelings of gut discomfort.
What we need to remember, however, is that most sporting events don’t give gold medals to the athlete that can exercise for the longest, but to the one that covers a given distance in the shortest amount of time. As such, even elite endurance athletes are required to reach high levels of exercise intensity in their events if they want to win, such as the final sprint seen in most endurance races.
So, in theory, there are certain situations where an LCHF diet may be advantageous. But how does this hold up in practice? Some studies do show an advantage to LCHF diets in a number of populations. Last year, researchers demonstrated that an LCHF diet (and in this case, a ketogenic diet) did not significantly harm performance in a 100km cycle time trial, and improved the participant’s peak power output in the sprint. This study was widely shared as proof of the effectiveness of LCHF/ketogenic diets, but, alas, the analysis was somewhat misleading, as I pointed out in a letter to the editor of the publishing journal. Essentially, the performance benefits were due to decreases in body fat. In a test where performance output is divided by weight, this obviously skews the results—especially for elite athletes, who often don’t have much body fat left to lose.
Other studies have reported a negative effect of an LCHF diet on anaerobic exercise performance (which is to be expected, given the primary energy system utilized); a decrease in training capacity in endurance training (but a decrease in body fat); and poorer strength training adaptations (but reduced body fat). One of the popular criticisms of these studies is that individuals must become adapted to LCHF diets (which is true) before they can realize the benefits, although the exact duration of such an adaptation phase is unclear, with no definitive answer given by LCHF proponents. This leads to my favorite joke of 2017: How long does it take to become fat-adapted? At least one week longer than the time period in the most recent study disproving LCHF for athletes. It must take a long time to become fat-adapted, given that this athlete followed an LCHF diet for 32 weeks, culminating in his worst performances ever.
Analyzing the Research
So far, the majority of research in this area has taken place with non-elite athletes, with the majority of performance improvements, if any, coming from reductions in body fat. Elite athletes are a different kettle of fish, however, and often have little excess body fat to lose. A series of studies from researchers at the Australian Institute of Sport on elite race walkers—exactly the type of athletes you’d expect to get a benefit from LCHF, given the (relatively) low intensity of their event—illustrated this nicely. The LCHF diet led to no improvements in a 10km time trial performance following a three-week training block, while those athletes consuming either a high carbohydrate or periodized carbohydrate diet did see improvements.
As such, for now, it appears that an LCHF diet has little to offer the majority of elite athletes, but may be useful for recreational athletes—particularly if they have higher levels of body fat. There is the potential that some periods of LCHF eating around training sessions, in the form of carbohydrate periodization, may enhance some specific training adaptations, although whether these adaptations manifest as performance improvements is unclear.For now, LCHF diets have little to offer most elite athletes, but may help recreational athletes. Click To Tweet
The best approach for elite athletes may, therefore, be a mixed approach—as suggested in the most sensible paper I’ve seen on the subject. One area where a low carbohydrate diet may potentially be useful is in managing weight (and by this, I mean losing weight fairly quickly) in weight class sports, such as Olympic weightlifting and various combat sports. While we don’t yet have a definitive answer as to the impact of an LCHF diet on elite athlete performance, we are, in my opinion, getting close. However, further research in this area is required to answer the following:
- After sufficient adaptation to low carbohydrate feeding, are there any performance advantages to elite endurance athletes following an LCHF diet? At present, the fairly limited research suggests no, but the main argument is that this is due to insufficient adaptations.
- After sufficient adaptation to low carbohydrate feeding, are there any performance advantages to elite speed-power athletes following an LCHF diet? Given the energy system requirements of these sports, I would suggest that the answer is almost certainly no, outside of reductions in body fat.
- What is the impact of ketone ester (a supplement that can rapidly mimic the effects of a ketogenic diet) when ingested by elite athletes?
- What is the impact of LCHF diets on training adaptations in elite athletes? At present, the research suggests that some periods of low carbohydrate intake may enhance training adaptations in endurance athletes (although, at present, this is largely theoretical), while other research suggests a prolonged LCHF diet during heavy training may negatively affect immunity, which could be problematic.
Why Does This Matter?
Athletes are always looking for an edge, and they often focus on the trends seen on social media and promoted by biohackers. At present, the use of LCHF appears to be potentially harmful to elite athlete performance, and so by increasing the body of evidence in this area, we will get a better idea of whether an LCHF plan is ever appropriate for elite athletes. We will also see how factors such as athlete event and training status alter the use of LCHF, along with whether and how to utilize periodized nutrition approaches to performance that involve short- and long-term LCHF use.
Is Caffeine Really Ergogenic for Everyone?
Caffeine is one of the most well-established, well-replicated performance-enhancing substances in sport—and the best news of all is that it’s completely legal. Athletes are fully aware of this, which is why roughly 75% utilize caffeine either immediately before or during competition. However, while, on average, caffeine demonstrates performance-enhancing effects across a variety of exercise types, when studies report individual subject data, we tend to see variation in how much performance benefit an individual gets from caffeine.
A famous example of this comes from a study published by Jenkins and colleagues. Here, the researchers gave subjects three different caffeine doses (1, 2, and 3 mg/kg), along with a placebo, and got them to undertake a 15-minute maximum cycle time trial. On average, although there was no performance enhancement from 1 mg/kg of caffeine for the majority of subjects, four of the 13 did show a performance improvement at that dose. Comparatively, while there was, on average, a performance-enhancing effect from 3 mg/kg of caffeine, two subjects performed worse with that caffeine dose than with no caffeine at all, and seven experienced less of a performance benefit than at lower doses of caffeine.
Based on this, and other studies reporting variation in caffeine’s ergogenic effects, it appears that caffeine can have a different effect on different people. This was the subject of a paper I wrote last year, exploring inter-individual variation in caffeine response. One of the factors that may affect how much caffeine enhances performance is an individual’s genotype.An individual’s genotype is one factor that may affect how much caffeine enhances their performance. Click To Tweet
A gene called CYP1A2 determines how quickly you metabolize caffeine; as a result, people are termed “fast” (AA genotype) or “slow” (AC/CC genotype) metabolizers of caffeine. A study from 2012 explored the impact of this gene on the ergogenic effects of caffeine. In this study, the authors got subjects to undertake a 40km cycle time trial under two conditions: with 6 mg/kg of caffeine, or placebo. They found that caffeine had a greater performance-enhancing effect in AA genotypes—improving performance by almost 5%–than C allele carriers, whose performance increased by around 2%.
Since that initial study, there were a handful of others, mainly reporting no effect of that gene. However, these studies tended to be underpowered, which may have made them unable to detect the small changes we would expect this gene to have. Then, earlier this year, a research group from Canada published a large-scale study on 101 athletes, exploring the impact of CYP1A2 on the effects of caffeine in a 10km cycle time trial. This is important because it:
- Had a sufficiently large sample size to detect the potentially small effects of the gene.
- Had a decent amount of CC genotypes.
On this second point, most previous studies have combined AC and CC genotypes into the “slow” metabolizers group, in part because the CC genotype is quite rare, occurring in only around 10% of people. With smaller studies, this means that there are often only one or two CC genotypes; this study had eight. The authors utilized two caffeine doses—2 and 4 mg/kg—along with a placebo. The results from the study as a whole were that 4 mg/kg, but not 2 mg/kg, of caffeine improved time trial performance compared to placebo.
What the authors then did was stratify for genotype, with some interesting findings. For AA genotypes (fast metabolizers), both caffeine doses enhanced performance compared to placebo. For AC genotypes, neither caffeine dose improved performance compared to placebo; caffeine appeared to be neutral for these individuals. For CC genotypes, 2 mg/kg of caffeine did not enhance performance compared to placebo, while 4 mg/kg made their performance much worse compared to placebo. These findings, therefore, suggest that for around 10% of the population, higher doses of caffeine (in this case, 4 mg/kg) can be harmful to performance, while for around 40% of the population (the expected frequency of AC genotypes), caffeine potentially has no beneficial effect when compared to placebo.
Since this study, a second paper from an Iranian researcher was published. In this study, the author explored the influence of CYP1A2 and caffeine on resistance training, specifically muscular endurance. The main finding of this study was that 6 mg/kg improved muscular endurance only in AA, and not in AC/CC genotypes (they were grouped together due to a lack of CC genotypes).
These results caused some significant cognitive dissonance for me. I used caffeine a lot during my career, and yet I possess the AC genotype for CYP1A2. Was I just wasting my time? Reflecting on this, I started to question the applicability of both the previous caffeine studies discussed above. What the first researchers found is that 4 mg/kg harmed performance in CC genotypes when consumed ~60 minutes pre-exercise—but what if they consumed either a different dose of caffeine, or the same dose but much earlier prior to exercise?Time—and new research—will tell whether everyone can get the performance benefits of caffeine. Click To Tweet
This potentially makes sense: One of the proposed mechanisms for why slow metabolizers see a reduction in performance is that the downstream metabolites of caffeine are also performance-enhancing; slow metabolizers, therefore, perhaps need longer periods of time to metabolize caffeine to these by-products, and therefore harness their performance-enhancing effects. In a letter to the editor, I proposed this theory, and I know of at least one research group that is seeking to test my hypothesis. Time will tell whether everyone can get the performance benefits of caffeine, or whether, as the current results suggest, for some people, consuming caffeine prior to exercise may well harm performance.
Why Does This Matter?
A very high percentage of athletes consume caffeine, both pre-training and pre-competition. Based on the results of recent research, up to 50% of these athletes may not be getting a performance benefit from caffeine, or worse, may be harming their performance by consuming caffeine. Given that caffeine is a widely utilized, well-established ergogenic aid, uncovering the impact of CYP1A2, along with other genes, on the performance benefits of caffeine has the potential to massively affect performance.
Are Isometric Loading Exercises as Effective as Eccentric Loading Exercises for Hamstring Injury Prevention?
Hamstring strain injuries are very common in sport at all levels. During my career, I suffered serious, season-defining hamstring injuries across four separate years. One of them prematurely curtailed my 2010 competitive season, and another left me facing an uphill, but ultimately successful, battle to qualify for the Beijing Olympics. Research shows that hamstring injuries are common in pretty much every sport that requires high-speed running. During the 2016-2017 Premier League soccer season, for example, 27% of all injuries affected the hamstring muscle group; separate research has shown that hamstring injuries represent the most common form of non-contact injuries in athletics, rugby union, cricket, basketball, Australian Rules football, and American football.Hamstring injuries lead to significant costs, as well as an increased future risk of other injuries. Click To Tweet
Clearly, hamstring injuries are common, but they also exert significant costs. At the elite sport level, even if a player is unavailable to compete, the team often still has to pay him. In individual sports, such as athletics, if you can’t race due to injury, you don’t get paid. But the financial implications are not the only costs of a hamstring injury; previous injury appears to increase the risk of both a future hamstring injury and injuries of other kinds, as well as reducing future physical performance.
As such, over the last 20 years or so, there has been an increased interest in understanding the causes of hamstring injuries. Over the last five years or so, there has been a war declared on hamstring injuries, with numerous research groups exploring different exercise modalities as a means to reduce the risk of such an injury, leading us to have a pretty good understanding of what is going on. When we injure a hamstring muscle during high-speed running, it most commonly occurs during the late swing phase, where our hamstrings act to reduce the forward movement of the lower leg, in preparation for it to be moved forcefully towards ground contact. In general, this process is thought (more on this in a minute) to require an eccentric contraction of the hamstring, where the muscle lengthens under load.
Eccentric contractions are uniquely damaging, as they occur under high loads, forces, and speeds, which can often lead to damage at the z-discs, the areas that delineate each individual portion of a muscle fiber. Indeed, lower levels of eccentric strength have been shown to increase the risk of hamstring injury, and increasing the eccentric strength capabilities of the hamstring reduces the risk of future injury. Additionally, one of the adaptations commonly seen following a period of eccentric loading is an increase in muscle fascicle length, with shorter muscle fascicles a second risk factor for hamstring injury. As such, we can be pretty sure—and indeed, almost certain—that eccentric loading exercises are a useful method to reduce the risk of hamstring injury, which has led to the popularization of exercises such as the Nordic Hamstring and Yo-Yo Hamstring exercises, both of which have demonstrated effectiveness at reducing the rate of hamstring injuries.We can be pretty sure that eccentric loading exercises are useful to reduce hamstring injury risk. Click To Tweet
However, eccentric loading exercises, including Nordics and Yo-Yos, are often associated with increased muscle soreness, which can reduce their uptake. Indeed, even though we know eccentric loading exercises are effective, compliance to them is often poor, which means that they don’t reduce hamstring injuries as much as we might hope.
Over the last couple of years, some research groups have become more interested in the use of isometric loading exercises as a means to reduce hamstring injuries. This school of thought is primarily driven by two researchers from the Netherlands, Frans Bosch and Bas Van Hooren. They suggest that, in actual fact, the hamstring muscle acts isometrically, not eccentrically, during the late swing phase of sprint running. It is very hard to either prove or disprove this theory in humans, because no one has yet been able to develop a method of observing the muscles inside the leg (most likely via ultrasound) during high-speed running.
As a result, most of the evidence underpinning Bosch and Van Hooren’s hypothesis is based on animal studies and predictive modeling—which doesn’t necessarily mean they’re wrong, but it is something to be aware of. Based on their belief that the hamstring muscle acts isometrically, and not eccentrically, during the swing phase of sprint running, Bosch and Van Hooren logically believe that isometric, and not eccentric, loading exercises are likely to be more effective at reducing the risk of hamstring injury. Examples of these types of exercises include the single-leg Roman chair exercise, which has some early evidence demonstrating its effectiveness.
An additional potential advantage of isometrics over eccentrics is that isometric exercises promote much less muscle damage and soreness. Given that one of the main reasons eccentric hamstring exercises are poorly adhered to within sport—and therefore don’t reduce injury prevalence—is due to the high levels of soreness experienced, this makes isometric hamstring exercises a viable alternative.
So far, the evidence underpinning isometric hamstring exercises is limited, especially compared to the high-level evidence, including randomized controlled trials and meta-analyses, supporting the use of eccentric exercises. As such, from a strictly evidence-based perspective, we should be programming eccentric hamstring exercises as a method to reduce hamstring injury rates. However, from a pragmatic standpoint—and remembering that much of real-life coaching and sports science support has to be pragmatic—we have to consider whether isometrics would hold more real-world effectiveness if their uptake and adherence rates were greater, and whether the exercises themselves are effective.
As such, we need studies exploring the use of isometrics, both as a “predictor” of hamstring injury (i.e., is lower isometric hamstring strength associated with an increased risk of hamstring injury, and is this association stronger than with eccentric hamstring strength?), and as a means to reduce hamstring injury prevalence. Additionally—and this will be a major challenge—we need to attempt to better understand whether the hamstring muscle operates isometrically, as Bosch and Van Hooren claim, or eccentrically during the late swing phase of high-speed running.
Finally, if isometric exercises are effective at reducing hamstring strain injuries, we need to view their adherence rates within the real world: Do teams utilizing isometric exercises have greater adherence and, as a result, fewer hamstring injuries than those utilizing eccentric exercises? Getting closer to the answer could have a large impact on the reduction of hamstring injuries, but, in the meantime, it’s probably best to program both into your injury prevention work.
Why Does This Matter?
Because hamstring injuries are so prevalent within sport, researchers have long attempted to understand how to reduce their occurrence. A great body of research suggests that eccentric hamstring exercises reduce the risk of hamstring injuries by increasing eccentric muscle strength and muscle fascicle length. However, recently some researchers have suggested that the hamstrings primarily act isometrically during the late swing phase of running, and as a result, we should be utilizing isometrically focused strength exercises to mitigate the risk of hamstring injury.Isometric hamstring exercises tend to cause less soreness, which should increase athlete adherence. Click To Tweet
This is an attractive option, because isometric hamstring exercises tend to cause less soreness, which will likely increase their adherence. As a result, a better understanding of the real-world effectiveness of isometrics versus eccentrics could have important implications on the risk of hamstring injury.