"Not one of nature's throwers": Understanding biomotor abilities - part 2

Emergent Abilities

Power: Power, from a technical perspective, is the rate at which work is performed. When this definition is applied to strength and condition, we can think of power as the rate at which force is being generated. Thus, a 500 lbs squat might last for a few seconds and although a significant amount of force is generated, it is generated very slowly, which taps into more maximum strength. We can compare absolute strength in the squat with true power in faster movements such as the vertical jump or the power clean, where the absolute amount of force is important, but not as important as the rate at which that force is produced. Thus, power is an emergent property of strength, speed, and (for more complex body movements) coordination.

Muscle Endurance (Short/Med/Long Durations): Muscle endurance, as mentioned in the previous post, refers to a muscles ability to maintain a certain level of work over time. At different durations of activity the limiting factor in endurance changes from the more neurological to the more metabolic. For short durations (ME-S), neural drive and the phosphagen system are limiting factors in the muscles performance.

For medium durations, the limiting factor is more metabolic, but rather than being an issue of using up energy substrates the issue is lactic acid build up and pain. During moderate intensity exercise the level of lactic acid produced by glycolysis is low enough for it to be absorbed quickly, but with high-intensity exercise lactic acid is produced faster than the body can absorb it. This lactate threshold is marked by an increased blood concentration of lactic acid, an increase in hydrogen ions, and an increased acidity which causes fatigue (perceived pain) and reduces the power of muscle contractions.

In long duration exercise, the limiting factor is the energy substrate. Thus, when intrafusal glycogen stores are depleted, there is little fuel left in the athletes tank. Endurance runners, cyclists, and triathletes are probably familiar with this unfortunate state, and they call it "bonking". Interestingly, you can bonk for a number of different reasons and feel the effects in very different ways. If you have depleted your muscle glycogen stores, your brain will feel fine, but your legs stop working. On the other hand, if you have depleted your blood glucose stores, you brain is running out of fuel and will start to slow down even when your legs are feeling fine.

Maximum Speed: Maximum speed is the top a speed a person can achieve regardless of time. It is simply the peak speed that you can hit, it does not matter if you hit that speed after o.3 s or 30s and it does not matter if you maintain that speed for 10 s or a minute. Maximum speed is an emergent property of a persons strength, speed (in the sense of neural drive), and coordination. When seeking to improve your speed any one of these abilities can be developed separately or in tandem. For instance, a sprinter might want to work on their leg strength, because more forceful contractions in the muscle will create more push off the ground and increase the distance covered in each stride. Or, the sprinter might want to work on developing the frequency and duration with which they can maintain neural drive to the muscle. Finally, a sprinter with good strength and neural drive might need to improve the efficiency of their stride by working on coordination. Working with a good coach on developing the proper mechanics for your body type (rather than just mimicking the mechanics of a good sprinter) is a critical, but often unappreciated aspect of training maximum speed.

Power Endurance: Power endurance is, as the name suggests, the ability to produce powerful movements repeatedly. Power endurance is incredibly taxing on the body's muscles, tendons, and nervous system because the muscles are operating above their lactate threshold and still required to produce maximal contractions. Middle distance runners, rock climbers, sprint swimmers, and cross-fit enthusiasts focus on developing power endurance. (... see cross-fitters, I'm showing you love...)

One of the limiting factors in power endurance is the bodies lactate threshold (the point at which lactic acid starts to accumulate in the blood stream). Below the lactate threshold, lactic acid that results from gylcolysis is effectively buffered, but at a certain point, hydrogen ions that result from hydrolysis within the muscle overwhelm bicarbonate buffers in the blood, resulting in acidification of the blood. In order to improve power endurance it is important to do interval training, where you have a "work" period near maximal levels followed by a "recovery" period in which you continue to work at very low percentages of your maximum. The details of effective and personalized interval training are too complex to give justice to here, but in general, interval training is an effective method of improving the body's lactate threshold and power endurance. Plus, interval training has the added benefit of improving endurance without the muscle catabolizing effects of high volume aerobic training.

Agility: Agility is the body's ability to change direction efficiently and is an emergent ability that results from the interaction of strength, speed, and coordination. Acceleration and deceleration are examples of agility. Agility is distinct from speed in that maximum speed requires no change in direction (i.e., the 100m is run purely straight ahead, tapping max speed, whereas the 30m shuttle requires several rapid changes in direction and continuous acceleration and deceleration, tapping agility). You can see the differential effects of agility and maximum speed in an elite 100m sprint. A more agile racer, with better acceleration is going to be faster out of the blocks, but a racer with a higher top speed will be moving faster as the race goes on. Thus, both acceleration and maximum speed are critical abilities to a sprinter.

Agility is required in just about all sports, but is perhaps most important in sports where the environment is either completely open or completely closed. An open environment means that the environment is undergoing continuous, unpatterned change. In open environments (such as combat sports, football, rugby, etc) agility is critical because an athlete must quickly and efficiently adapt to changes in their environment. In a closed environment there is no change in the environment other than changes initiated by the athlete (such as diving or gymnastics... imagine mounting a pommel horse to the back of a mechanical bull in a cowboy bar, suddenly shifting the environment from closed to open!). Thus, in closed environments, athletes can take advantage of the environment's stability to perform spectacular feats of agility.


A Few Training Prescriptions
It is important to recognize that athletes (beyond a young age) are not training for a general level of fitness, but are training to optimize certain biomotor abilities. There are several approaches to training optimization, but in general all of these training protocols rely on periodization. Periodization is a training program that emphasizes training different biomotor abilities throughout the year. Different sports follow different formats of periodization throughout the year based on (a) the needs of the sport and (b) the number of major competitions during the competitive season. Thoroughly understanding the needs of the sport allows coaches and athletes to preferentially train the most appropriate biomotor abilities and scheduling the training around major competitions helps to ensure that the athlete peaks at the correct time during the competitive season.

In general, periodization breaks the year (i.e., "the macrocycle") in to smaller training components ("meso-cycles"; such as the pre-season, competitive season, and off season). Within each of these meso-cycles different types of training are emphasized. For instance in the early pre-season athletes will spend timing developing a training base (anatomical adaptation to training) doing higher volume low intensity exercises, which helps to strengthen ligaments and tendons preventing injury later. As the pre-season progresses, the focus shifts to the development of maximum strength and maximum speed. Once the competitive season starts, the focus shifts based on the needs of the sport; power sports will focus on maintaining maximum power, whereas endurance sports will work muscular endurance of the appropriate duration. In the off season, coaches and athletes should encourage "active rest" and determine weaknesses or areas of improvement that the athlete can develop in the coming pre-season. This is a huge generalization, so I would encourage you to read this and this.

This type of progressive cycling throughout the macrocycle is referred to as "linear periodization" because the biomotor abilities being trained progress linearly from one meso-cycle to the next. An alternative and equally valid approach is nonlinear or undulating periodization, which posits the best way to optimize athletic performance is to shift the training focus within a "micro-cycle". That is, within a 10-day period some days should focus on power development, others on agility, and others on maximum strength with the number of days spent training a specific ability proportional to the needs of the sport (i.e., sprinters will have a lot of maximum speed and power days and few/no long endurance or agility days).

Personally, I like to hybridize the approaches when working with athletes and use linear periodization to shift the training focus on a larger scale (working on anatomical adaptation and maximum strength in the preseason and power in the competitive season) but within each meso-cycle I try to take advantage of nonlinear cycles. So within a meso-cycle focused on maximum strength development, on days when the athlete is feeling really good and fresh, we will train abilities with a larger neural component (such as power and speed). On days when the athlete maybe tired or just unmotivated, the focus will be abilities with a larger muscular component (such as endurance or strength). Thus, there is subtle variation within a meso-cycle, but there is even greater variation between meso-cycles.

“Not one of nature’s throwers”: Understanding Biomotor Abilities

Anyone who was on the Idaho State University track team between 2005 & 2007 knows that I cannot throw a javelin very far. This is a lamentable fact, but I’ve come to terms with it. I distinctly remember one practice talking with my friend and head coach Dave Nielson, and although I forget exactly what led up to his comment, I remember the comment distinctly. He said, “Well, you’re just not one of nature’s throwers.” I had to laugh because it was very true. My javelin throw was poor, my discuss was pedestrian, and when I threw a football … we can just say it was ugly and leave it at that.

What is really strange is how specific my throwing deficiency is. I can throw darts quite well, I’m good at bocce, and I distinctly recall one windy day at track practice when I skewered a plastic bag that was blowing across the in-field. How could I be so bad a throwing a javelin for distance and yet so much better at throwing the same javelin for accuracy? Part of the answer is that athletic talents, what I will call biomotor abilities, are highly specific. Different sports emphasize different biomotor abilities, and different people are born with or train to develop these abilities to different levels.

Consider two very fast people: Usain Bolt and Kenenisa Bekele (...whom I have chosen for their name recognition…). Bolt and Bekele are both undeniably fast, but they are fast in very different ways. (Bolt’s record is in the 100m at 9.58s; Bekele’s records are in the 5k = 12min 37.35s, and the 10k = 26min 17.53s). I can’t say what would have happened if Bolt had dedicated his life to being a distance runner, or if Bekele had desired to be a sprinter, but as it is Bolt has developed one set of biomotor abilities that make him very fast over a short distance, whereas Bekele has developed a different set of abilities that make him very fast over long distances.

So if both men are fast, fast stops being a useful term and we have to think about how they are fast. In the same way, in high level athletics it is not enough to say that someone is strong; we have to consider how they are strong. Studies of athletic training are very concerned with understanding this problem and as such have developed a rigorous taxonomy (i.e., system of classification) for biomotor abilities (Bompa & Carrera, 2005; Fleck & Kraemer, 1996). In this post, I’m going to break these abilities into dominant abilities (the five basic abilities that underlie athletic performance) and in the following post, I will discuss emergent abilities (more specialized skills that emerge from the interaction of dominant abilities).

Dominant Abilities

Strength. Strength is really one of the most fundamental of athletic abilities and it should always be trained with other biomotor abilities. There is a common misconception that strength training slows down athletes and negatively affects the development of flexibility and endurance. Empirical research shows that this is not the case (Dudley & Fleck, 1987; Sale et al., 1990; Nader, 2006). All strength technically is, is the maximum amount of force the body can produce (not taking into account the rate at which that force is produced). In this way, strength is useful ability to all athletes, regardless of if the sport is more of an endurance sport. In fact, a recent study looked specifically at strength training in cross country skiers and found that training programs designed to increase maximum strength did increase maximum strength but also improved work economy by increasing time to exhaustion (Hoff, Gran, & Helgerud, 2002). There is little truth to the idea the strength training decreases flexibility, but if you train like a body-builder (with high repetition, single-joint, uni-dimensional free weight training) you probably will lose flexibility. Fortunately, most athletes and their coaches do not train this way and use more functional, sport specific approaches. (Side note: If you are not a body builder, DO NOT TRAIN LIKE ONE!)

Endurance (Aerobic & Anaerobic Endurance). Endurance refers to the capability of the body to maintain a given level of work over time. From a physiological standpoint, the body’s metabolic systems are the limiting factors in endurance (that is, we can only endure as far as we have the energy substrates to do so). The body’s metabolic pathways breakdown into roughly three systems:

1. The Phosphagen System: a purely anaerobic (without oxygen) system.
2. The Glycolytic System: fast glycolysis is more anaerobic; slow glycolysis is more aerobic in nature.
3. The Oxidative System: this is the metabolic pathway most people think of when they talk about aerobic activity. Only carbohydrates can be metabolized for energy without the direct involvement of oxygen. (Intrafusal glycogen is the primary energy substrate for the body.)

Each of these systems is responsible for endurance, but at a different time scale. In general, shorter, high intensity exercise relies on the phosphagen system and fast glycolysis and your ability to maintain high intensities for shorter durations (power-endurance) is dependent on this system. As intensity decreases and duration increases, the metabolic emphasis shifts to slow glycolysis and the oxidative energy system (more traditional endurance).

The PHOSPHAGEN SYSTEM provides ATP primarily for short duration, high intensity activities. The kinase Myosin ATPase releases a phosphate from ATP (making ADP + P) which binds actin and myosin filaments in the muscle tissue and is critical for muscle contraction. Creatine Phosphate, which is stored in the muscle, supplies a phosphate group to ADP to reform ATP and allow for more strong muscle contractions. (This is one of basic principles behind creatine supplements; you will increase your interfusal stores of creatine phosphate allowing you to work longer at higher instensities; Green, Hultman, Macdonald, Sewell, & Greenhaff, 1996.) Type II (or fast twitch) muscle fibers contain greater concentrations of phosphagens than Type I muscle fibers, which partly why Type II muscle fibers are responsible for more powerful muscle contractions.

The GLYCOLYTIC SYSTEM breaks down carbohydrates –either glycogen stored in the muscle or glucose carried by the blood- to produce intrafusal ATP, which again, enables muscle contraction. Glycolysis comes in two flavors. The faster glycolytic pathway (cleverly dubbed fast glycolysis) converts pyruvate into lactic acid. The breakdown of pyruvate allows ATP to be released quickly, but at the price of lactic acid build up. Lactic acid accumulation directly interferes with muscle excitation and contraction because lactic acid prevents calcium from binding to Troponin, which prevents cross bridge formation between actin and myosin filaments in the muscle.

Lactic acid can be converted into Lactate by buffering mechanisms in the muscle and blood. Lactate can be cleared by oxidation within the muscle fiber, which is why high intensity workouts should be followed by a cool down to prevent delayed onset muscle soreness.

Fast Glycolysis: Glucose + 2P + 2ADP è 2 Lactate + 2ATP + H2O

The alternative, slower glycolytic pathway (termed slow glycolysis) also breaks glucose down into ATP, but only if oxygen is present in the system. If oxygen is present, pyruvate is not converted into lactic acid, but instead transported to the mitochondria and converted to Acetyle CoEnzyme A (CoA). This intervening process take more time (which why slow glycolysis is more important for activities of longer durations) but has the benefit of not building up lactic acid.

Slow Glycolysis: Glucose + 2P + 2ADP + 2NAD+ è 2Pyruvate + 2ATP + 2NADH +2H2O

The OXIDATIVE (AEROBIC) System: the oxidative system is the primary source of ATP at rest and during low intensity activities. Oxidative metabolism relies on the presence of oxygen to “burn” carbohydrates and fatty acids to produce ATP. As we saw in the phosphagen and glycolytic systems, during high-intensity aerobic exercise most of the energy comes from carbohydrates. With prolonged submaximal intensity, however, the energy substrate shifts from carbohydrates to proteins and fatty acids.

Speed. Speed is defined as the distance an object can travel in a given time. At the behavioral level, speed is easy to see in the displacement of an object such as a runner or a ball thrown, but as a primary motor ability, we are more interested in “neural drive” the ability for high frequency neural signals to recruit motor units. Adaptive changes can occur in the nervous system in response to training. Electromyography studies have shown the nervous system can adapt to training stimuli in a number of ways, including increased neuronal outflow, increased maximal firing efficiency, increased excitability and decreased inhibition of spinal motor neurons, and the down regulation of inhibitory pathways (Van Cutsem, Duchateau, & Hainaut, 1998; Aagaard, 2003).

How does this neural drive translate to speed? Consider an event like the 100m (the sprinters apotheoses). Lasting only 9-10s, this event is too short to have metabolism or muscular fatigue be a limiting factor (...even the phosphagen system would not be depleted over the course of 10s). So, what is the limiting factor in this event? The answer is neural fatigue (at least in part). For extremely powerful contractions that are close to the upper limit of a muscle's ability to generate force, neural fatigue can be a limiting factor in both trained and untrained individuals. In novice strength trainers, the muscle's ability to generate force is most strongly limited by nerve’s ability to sustain a high-frequency signal. After a period of maximum contraction, the nerve’s signal reduces in frequency and the force generated by the contraction diminishes. Thus, the ability to rapid turn muscles on and off that is required to maintain high levels of speed is not a property of the muscular system, but is a property of the nervous system! (Naturally, the muscular system contributes to speed as well, because more powerful muscles will reap larger benefits with increased neural drive, but the interaction of these two biomotor abilities is something that I will discuss later as an emergent property, maximum speed).

Coordination. Coordination, or control of movement, is the nervous systems ability to regulate both kinematic and kinetic parameters of movement to produce intended actions. Kinematics refers to the spatial properties of objects (e.g., limb positions, angles). Kinetics, nowadays referred to as dynamics, refers to the forces within a system (e.g., force of a single muscle, the interaction of torque from different joints).

Learning to control the motor system to accomplish a desired goal can generally be thought of as ‘coordination’ and has been the subject of many years of research (Wolpert, Ghahramani, & Flanagan, 2001). However, research on motor control often divides coordination into several different sub-categories, such as inter-limb coordination (Haken, Kelso, & Bunz, 1985), intra-limb coordination (Flash & Hogan, 1985), hand-eye coordination (Johansson, Westling, Bäckström, & Flanagan, 2001), locomotor coordination (Niizeki, Kawahara, & Miyamoto, 1996), and postural coordination (Collins & Luca, 1993).

Flexibility. Flexibility refers to the absolute range of motion in a joint or a series of joints, which is largely determined by the muscles, ligaments, and tendons that cross those joints. Flexibility in bony joints, such as the knee and elbow, is limited more by the bony structure than by these soft tissues. In joints with less structural stability, such as the shoulder, flexibility is much greater and much more dependent on the nature of these soft tissues.

Another internal factor that contributes to flexibility is muscular balance around the joints. That is, the strength of the muscles on either side of the joint (or adjacent to the joint) affects its range of motion. Agonist/antagonist pairs of muscles surrounding the joint create a sort of balance; when both of these muscles are sufficiently strong, they allow the joint to move through a fuller range of motion. If one side of the agonist/antagonist pair is underdeveloped, injured, or otherwise weak, joint motion will be compromised.

One of the most important factors that we can easily control to improve flexibility is temperature. At colder temperatures muscle tissue is more viscous, synovial fluid is more viscous, and stretch reflexes are suppressed, so raising the body’s core temperature prior to exercise is very important and improves flexibility (Shellock & Prentice, 1985). Recent research on the effects of warm-up and pre-competition stretching have shown that a warm-up is generally important because elevating body temperature increases muscle blood flow, reduces muscle viscosity, increases the sensitivity of nerve receptors, and an increases the speed of nervous impulses (Bishop, 2003; Shellock & Prentice, 1985). Stretching prior to competition is a more sensitive issue, and in general it is a good idea to avoid static stretching (traditional grab your toes and hold for 30s kind of stretching) and instead use dynamic, functional stretches that recreate the full range of motion the athlete will use in competition (Fletcher & Jones, 2004; Little & Williams, 2006).

Emergent Abilities

Emergent biomotor abilities come from the interaction of the dominant biomotor abilities (e.g. maximum speed and maximum strength determine power, which is the ability to rapidly generate force). In my next post I am going to define some of these emergent abilities and how to train them.

Vegetables are what my food eats...

There are thousands of people who will unflinchingly deliver dietary advice and proscribe radical changes to your diet as panacea to your psychological and physiological ailments. (At a party once I heard a stranger telling a friend about how he should stop eating soy because it was causing his back pain; I shuttered and then died a little). I do not want to be one of those polemic diet people. Under no circumstances do I want to be construed as one of those people... but I do want to do a blog post on nutrition and the human diet, so it's a risk I'm willing to take.

The good news is that I'm not a diet Puritan and I'm hear to tell you that it probably doesn't matter as much what you eat compared to the more important how much you eat. It is really difficult to judge any sort of "best" diet for modern humans to eat, because there is such wide range in the diets of modern humans. For instance, in the Inuit peoples of the arctic, the diet relies almost exclusively on the fat and proteins of marine mammals (Ho et al., 1972), but on the other end of the spectrum, the Aboriginal peoples of Australia thrive on a diet limited to a number of wild plant species with almost no meat at all (Gould, 1980). Thus, there is clearly a wide variety in what can be functional in the human diet.

However, there are a few dietary tenets, based on evidence from nutritional anthropology, that I think are important to adhere to, such as:

• decreasing the consumption of highly refined and processed foods
• increased consumption of "wild" fruits and vegetables
• preference for wild game or grass-fed game over grain fed cattle.

(I'm going to rely on a lot of evolutionary evidence to support the claims I make in this post, but I am not an advocate of the so-called "Paleo-Diet", for reasons that I will enumerate below).

With all of the technological and social innovation in how human beings produce, manage, and process food, there is growing and legitimate concern that these advancements have happened too quickly for human digestive physiology to adapt to them (Trowell & Burkitt, 1981). Which has led many people to support a diet akin to ancestral hunter-gather populations in order to avoid "diseases of affluence" that effect many first world nations (such as obesity, diabetes, coronary diseases, etc.). The problem is that these "Paleo-diets" are really based on conjecture about what hunter-gather populations ate and do not consider the variation in diets of early peoples or the true course of evolution for our digestive physiology. Thus, although I support the general idea of the Paleo-diet, I think most supporters of it have many of the details very wrong.

What do we know about the diet of early humans?
First of all, fossil evidence suggests that modern humans appear about 2.4 mya, but only developed agriculture in the last 12-14 thousand years. This does mean (as proponents of the Paleo-diet assert) that for most of out time on earth, modern humans subsisted using hunter-gather practices; using only wild types of plants and animals as food sources. The problem with diets that attempt to recreate this ancestral hunter-gatherer diet is the assumption that our digestive physiology became adapted to these practices leading to some "optimal" diet for all modern humans based on macro- and micro-nutrient in take of our ancestors.

This assumption is a problem for two reasons. First of all, hunter-gather diets were not at all uniform (based on evidence from contemporary hunter-gatherer populations and reconstructions of ancestral diets from fossil evidence; Ungar & Teaford, 2002). Second, and perhaps most importantly, there is little evidence to suggest human digestive physiology or nutritional requirements changed substantially during that period of our evolution (Milton & Demment, 1988; Milton, 1999). This can be seen in the fact that there are very few differences in the digestive physiology and nutritional requirements of human beings and other great apes.

In fact, those differences that do exist appear to have developed more in the last 12 thousand years post agriculture! For instance, human lactase synthesis in adulthood is a very recent evolutionary adaptation that has reached only a few populations of modern humans in response to the domestication of milk producing animals. To drastically summarize this evolutionary data, it appears that relatively few adaptations have occurred in the human diet in the last 2 million years, most of the adaptations that have occurred are largely regulatory, do not change human nutritional requirements, and are the result of adaptations to the advent of agriculture.

Hmmm... 2.4 million years is a pretty long time, and certainly enough time for evolutionary adaptations to occur, so why didn't they? It might be a question of scale... our 2.4 million years as modern humans pales in comparison to the evolutionary time we spent as protohumans. It is in this time period that our digestive physiology and nutritional requirements were really established. The evidence for this is again comparative studies of nutrition between humans and the other great apes. Both comparative and experimental data show that striking similarities in anatomy and digestive kinetics (e.g., how food moves through your gut) between humans, chimps, orangs, and gorillas (Milton, 1987; Milton and Demment, 1988, Caton, 1997). So in this way I believe supporters of ancestral diets are correct, if modern humans deviate too much from ancestral ways, further compounded by radical changes in lifestyle and physical activity, problems will arise in the form of diseases of affluence.

I would strongly recommend a greater reliance on wild foods as a basis for healthy diets. Wild fruits and vegetables contain greater nutritional density and greater interspecies variation in nutrients than their cultivated counter parts (Conklin-Brittain & Wrangham, 2000; Oftedal et al., 1991). There are similar advantages in consuming wild game to grain-fed cattle (O'Dea, 1992), and the dietary need for animal based proteins is less than you might think (Carpenter, 1994). Although, much to the chagrin of vegetarians and vegans everywhere, the consumption and especially the cooking of meat played an important role in the evolution of the human brain.

To conclude, information on the diets and health of recent and contemporary traditional peoples shows a wide range of highly successful human diets. From hunter-gathers to small-scale agriculturalists who also eat wild foods, we can see all such societies are free of the so-called diseases of affluence whether the diet is made up primarily of proteins and fatty acids acquired from animal source, based on wild plant foods, or even a single cultivated starchy carbohydrate supplemented with wild foods (Lee, 1968; Ho et al., 1972, Neel, 1977; Woolfe & Poats, 1987). Therefore, I would argue, there is not some best human diet, only best human diets.

By that I mean there is not some ideal Paleolithic diet or marco/micronutrient profile, but we should look instead to the shared features of the diets (and lifestyles) of many different traditional societies that spell the difference between their health and ours (Milton, 2000).

I would argue that recent technology has allowed us to circumvent natural barriers in our digestive physiology. Processing, condensing, refining, and otherwise altering both plant and animal foods have allowed us to ingest more energy per day than was otherwise possible with less industrialized food sources. And of course, on the other side of this coin, most of us lead sedentary lives in comparison with more traditional peoples who typically carry out physical activities (often stenuous) for eight hours or more per day; placing a premium on energy expenditure to balance out our energy intake.