question: Why do you get tired faster when running with clenched fists?
comment: URL_0 Basically you are using energy to close your hands. If you leave them in a more relaxed position it will use less energy, and allow it to be more spent on running. The source answers your question to the T
passages: Fatigue is a prominent factor in sprinting, and it is already widely known that it hinders maximal power output in muscles, but it also affects the acceleration of runners in the ways listed below.
  
  Section::::Fatigue effects.:Submaximal muscle coordination.
   Section::::Fatigue effects.:Hindrance of effective force application techniques.
   The kinetics of running describes the motion of a runner using the effects of forces acting on or out of the body. The majority of contributing factors to internal forces comes from leg muscle activation and arm swing.
  
  Section::::Kinetics.:Leg Muscle Activation.
   The muscles responsible for accelerating the runner forward are required to contract with increasing speed to accommodate the increasing velocity of the body. During the acceleration phase of sprinting, the contractile component of muscles is the main component responsible for the power output. Once a steady state velocity has been reached and the sprinter is upright, a sizable fraction of the power comes from the mechanical energy stored in the ‘series elastic elements’ during stretching of the contractile muscles that is released immediately after the positive work phase. As the velocity of the runner increases, inertia and air resistance effects become the limiting factors on the sprinter’s top speed.
   With all forms there is an obvious backward lean relative to normal running's forward lean, which can shift the stress of the other muscle fibres a small degree.
   In distance running, an athlete may attempt to improve performance through training designed to improve running economy. Running economy has been found to be a good predictor of race performance; it has been found to be a stronger correlate of performance than maximal oxygen uptake (VO max) in trained runners with the same values (Saunders, 2004). The literature relating to RE is vast and the determinants of RE supported by empirical data.
  
  Section::::Factors affecting running economy.
   Section::::Running economy.:Factors influencing running economy.
   In humans, the PTS is believed by some to occur at critical levels of ankle dorsiflexor moments and power. Dorsiflexor muscles show high levels of activation when walking near the PTS and human subjects describe feeling fatigue in these muscles. Ratings of Perceived Exertion (RPE) also decrease after the transition to running, despite a higher energetic expenditure.
   Section::::Running economy.
   Low level theories exist that suggest that fatigue is due mechanical failure of the exercising muscles ("peripheral fatigue"). However, such low level theories do not explain why running muscle fatigue is affected by information relevant to cost benefit trade offs. For example, marathon runners can carry on running longer if told they are near the finishing line, than far away. The existence of a central governor can explain this effect.
  
  Section::::See also.
  
  BULLET::::- Central governor
  
  BULLET::::- Deployment cost–benefit selection in physiology
  
  BULLET::::- Evolutionary medicine
  
  BULLET::::- Health science
  
  BULLET::::- Management control system
  
  BULLET::::- Mind–body
  
  BULLET::::- Neural top–down control of physiology
   This view was largely unchallenged until the late 1980s. Since that time, several studies have shown that transitioning from walking to running actually resulted in an increase in energy expenditure, while other studies have supported an energetic benefit from the transition. In the time since the energetics optimization view was first challenged, a number of mechanical, kinetic, and kinematic factors have been explored to explain the transition. Weak to moderately strong correlations have been found between several variables and the PTS, but work from a variety of researchers in the 1990s and 2000s agrees that ultimately it is fatigue and discomfort (or imminent fatigue/discomfort) in the tibialis anterior and other dorsiflexor muscles of the ankle that is the primary stimulus for the transition from walking to running in humans.
   Aerobic capacity depends on the transportation of large amounts of blood to and from the lungs to reach all tissues. This in turn is dependent on having a high cardiac output, sufficient levels of hemoglobin in blood, and an optimal vascular system to distribute of blood. A 20 fold increase of local blood flow within skeletal muscle is necessary for endurance athletes, like marathon runners, to meet their muscles' oxygen demands at maximal exercise that are up to 50 times greater than at rest. 
   Section::::Running economy.:Measures of economy.
   In "The Lore of Running", Tim Noakes, a professor of exercise and sports science at the University of Cape Town, and also recreational runner, describes a number of variables that may affect running economy: vertical motion while running, the ability of the muscles to absorb energy during the shock of landing and transfer it to push-off, biomechanical factors, technique and type of activity, fitness and training, age, fatigue, gender, race, weight of clothing and shoes, and environmental conditions.
   Uncertainty exists in regards to how lactate threshold effects endurance performance. The contribution of one's blood lactate levels accumulating is attributed to potential skeletal muscle hypoxemia but also to the production of more glucose that can be used as energy. The inability to establish a singular set of physiological contributions to blood lactate accumulation's effect on the exercising individual creates a correlative role for lactate threshold in marathon performance as opposed to a causal role.
  
  Section::::Alternative factors contributing to marathon performance.
  
  Section::::Alternative factors contributing to marathon performance.:Fuel.
   Researchers once attributed fatigue to a build-up of lactic acid in muscles. However, this is no longer believed. Rather, lactate may stop muscle fatigue by keeping muscles fully responding to nerve signals. The available oxygen and energy supply, and disturbances of muscle ion homeostasis are the main factor determining exercise performance, at least during brief very intense exercise.
   Section::::Physiology of long-distance running.:Factors.:Lactate threshold.
   Section::::Muscle tone.
  
  Although muscles can be in a relaxed state, muscles have a general resting level of tension. This is termed muscle tone and is maintained by the motor neurons innervating the muscle. Its purpose is to maintain posture and assist in quicker movements, since if muscles were completely loose, then more neuronal firing would need to take place. 
   While necessary for sports and ordinary motions, this protective reaction is counterproductive for stretching, i.e., lengthening muscles.
  
  Section::::A history of active stretching.
  
  BULLET::::1. Sir Charles Sherrington conceptualized the principle of reciprocal innervation circa 1904 and demonstrated it circa 1913.
  
  BULLET::::2. A. D. Munrow's work proposed these principles for ‘active’ mobilizing exercises. 1962
   Both the architecture and type of muscle play a crucial role in determining foot contact time and production of GRF. In humans, it has been shown that sprinters have longer muscle fascicle lengths and smaller pennation angles than non-sprinters. This contributes by increasing the muscle's shortening velocity. Other studies have shown that particular muscle fiber types are favored in sprinters versus non-sprinters, as well as within different levels of sprinters. Faster individuals tend to have a greater percentage of Type II (fast-twitch) muscle fibers. Higher percentage of fast-twitch muscle fibers lead to increased force production capability, as well as increased speed of contractions leading to shorter contact times.
   Running economy
  
  Running economy consists of many physiological and biomechanical factors that contribute to running performance, and is measured to quantify energy utilization while running at an aerobic intensity. Oxygen consumption (VO) is the most direct method for measuring running economy, as the exchange of gases in the body, specifically oxygen and carbon dioxide, closely reflects energy metabolism. Those who are able to consume less oxygen while running at a given velocity are said to have a better running economy.
   Central nervous system fatigue is a key component in preventing peripheral muscle injury. The brain has numerous receptors, such as osmoreceptors, to track dehydration, nutrition, and body temperature. With that information as well as peripheral muscle fatigue information, the brain can reduce the quantity of motor commands sent from the central nervous system. This is crucial in order to protect the homeostasis of the body and to keep it in a proper physiological state capable of full recovery. The reduction of motor commands sent from the brain increases the amount of perceived effort an individual experiences. By forcing the body through a higher perceived intensity, the individual becomes more likely to cease exercise by means of exhaustion. Perceived effort is greatly influenced by the intensity of corollary discharge from the motor cortex that affects the primary somatosensory cortex. Endurance athletes learn to listen to their body. Protecting organs from potentially dangerous core temperatures and nutritional lows is an important brain function. Central nervous system fatigue alerts the athlete when physiological conditions are not optimal so either rest or refueling can occur. It is important to avoid hyperthermia and dehydration, as they are detrimental to athletic performance and can be fatal.
   This hypothesis was disregarded and further research upon exercise fatigue was modeled in terms of it being due to a mechanical failure of the exercising muscles ("peripheral muscle fatigue"). This failure was caused either by an inadequate oxygen supply to the exercising muscles, lactic acid buildup, or total energy depletion in the exhausted muscles.
  
  Section::::History.:Tim Noakes.
  
  Tim Noakes, a professor of exercise and sports science at the University of Cape Town, in 1997 has renewed Hill’s argument on the basis of modern research.
   BULLET::::- Sand running creates less strain on leg muscles than running on grass or concrete. This is because sand collapses beneath the foot, softening the landing. Sand training is an effective way to lose weight and become fit, as more effort is needed (one and a half times more) to run on the soft sand than on a hard surface.
   The dorsiflexor muscles are small relative to other major muscles of the leg involved in locomotion such as the gluteals, hamstrings, quadriceps and the plantarflexors of the ankle. These muscles must exert large amounts of force at two points during the walking stride at high speeds: 1) The beginning of the stance phase of walking, when the heel touches down and the raised toes must be stabilized to avoid "slapping" the forefoot on the ground. 2) During the swing phase, the trailing leg is moved ahead of the foot planted on the ground and the toes must be raised to avoid colliding with the ground. Because of their relatively small size, these muscles are prone to fatigue quickly when asked to exert large amounts of force during high speed walking. The transition to running reduces the load on the dorsiflexor muscles and reduces the feeling of discomfort associated with fatigue of these muscles.
  