Science of Running by Steve Magness

In looking at a race, in terms of the dominant energy system, the crossover point where aerobic energy is the majority supplied occurs at around 45sec (Hill, 1999). For this reason, if we look at relative energy system contribution for different races, anything over 400m uses the aerobic system to supply the majority of its energy. For competitive males a variety of studies have found that the energy contribution between aerobic and anaerobic systems is 60% aerobic and 40% anaerobic for the 800m, 77%/23% for the 1,500m, and 86%/14% for the 3,000m races (1) – page 29
What they then looked for was what areas of the brain were active just prior to the subject’s decision to “give in” and have “task failure.” They found that the insular cortex and the thalamus showed increased activation… their previous study made them speculate that the insular cortex might play a key role in evaluating sensory feedback and communicating with the motor cortex to maintain homeostasis (2) – page 44
Okano and colleagues used tDCS over the temporal and insular cortex 20 minutes before doing a max cycling exercise (2013). The study participants, national class cyclists, improved their peak power output by 4%, which is a pretty large performance increase. While the complexity of the subject is astounding, the fact that stimulating the temporal and insular cortex can improve performance surely lends credence to the idea that the brain is the master controller. (3) – page 45
cyclists were put through self-paced time trials after the administration of an SSRI in hot conditions. What they found was that subjects needed longer (2.3min) to complete the same workload, but more interestingly the pacing strategies between the placebo group and the SSRI was different. The SSRI subjects were slightly slower during the middle portion of the time trial, but more significantly, they were not able to “kick” at the end. As we will see later, the “kick” is a result of a combination of reserve and drive. The fact that an SSRI eliminated the kick means that serotonin plays a role in fatigue and that perhaps, as Roelands put it, “increased serotonergic activity in the brain may block access to the reserve capacity (4) – page 46
When exercising in hypoxic conditions, not only does oxygen delivery decrease but also cerebral oxygen content. What is interesting is that this decrease in cerebral oxygen is associated with a decrease in voluntary activation of both muscles involved in the exercise and muscles not involved in the exercise (Goodall, 2012). So a reduced cerebral oxygen level causes a decreased ability to recruit muscles beyond those that are already used and fatigued… Further corroborating this is the finding that central neurons can sense reduced oxygen delivery and alter their activity as a result (Ando et al. 2012). What all of this means is that cerebral oxygen content can change motor drive (5)- page 48
the brain uses a teleoanticipation system where the knowledge of how long the race is, the degree of rise in core temperature, and other factors are used to anticipate reaching that critical core temperature. Essentially, if your core temperature is rising too quickly for you to finish the race unscathed, the brain will start shutting you down early to slow your pace and thus slow the rate of heat accumulation (6) – page 48
They had their subjects do time trials on three separate occasions. Once in cool environment (22 degrees Celsius), once it hot conditions (31 degrees), and once in a deceived condition where they were told that it was cool, but in actuality it was 32 degrees. With this simple manipulation of the thermometer came profound changes in performance. Not surprisingly, the cyclists performed more work and covered a greater distance in the cooler temperatures, but as you may have guessed, when they thought they were performing in moderate temperatures but were actually performing in hot conditions, the cyclists covered the same distance and had the same power output as when they were actually in cool conditions (7) – page 49
They had nine cyclists complete four 4km time trials with the first two being used to ascertain a baseline. On the next two time trials, they had participants race an avatar and this is where the deception came in. They were told that the avatar simply represented their best performance at baseline, which was true for trial number three. But for the fourth trial, they programmed the avatar to go just faster (102%) than their baseline performance. As you might expect now, the deception resulted in a faster performance than any other time trial completed. What is notable about this study is that they found that difference was in anaerobic contribution to the exercise. The deceived trial resulted in a greater anaerobic output at 90% of the time trial. What does that mean? Simply that the cyclists were able to increase power output earlier, and more so, at the end of the time trial. In essence, they were able to kick longer and stronger. The implication for this is that they were able to tap into their “anaerobic reserve” to a much greater amount (8) – page 49
respiratory muscles compete for blood flow with skeletal muscle. Due to this competition, diaphragm fatigue can occur at intensities greater than 80% VO2max ( – page 61
They found that endurance was significantly increased by 15% in the decreased respiratory muscle load trial, while endurance was decreased by 14% when increased respiratory muscle resistance was applied (10) – page 61
using inspiratory muscle training improved performance over the 20km and 40km trials by 3.8% and 4.6% when compared to a control group and resulted in a reduction of respiratory muscle fatigue post trial. (11) – page 61
studies investigating respiratory training have been mixed. Several studies have seen increases in performance in cyclists and rowers (12) – page 61
out of eight studies done, six showed improvements in performance following respiratory training (13) – page 61
an increase in H+, which is a proton that dissociates from lactate and would decrease the pH, may impair muscle contractility (14) – page 79
the buffering capacity of 6 elite cyclists was found to be significantly related to their performance in a 40km time trial (15 – page 79
Not only does an increase in mitochondria size cause a decrease in lactate, but an increase in mitochondrial enzymes decreases lactate too (16 – page 81
several studies have established a relationship between mitochondrial enzyme activity and the LT (17 – page 81
RE could explain 65% of the variation in race performance among the group of 12 runners (18 – page 88
Evidence of the impact of the SSC on RE can be seen by the fact that muscle stiffness strongly correlates with RE… stiffer muscles surrounding the ankle and knee created an increased SSC response, which resulted in greater force on the subsequent push off (19) – page 89
a forefoot strike results in a shorter ground contact time and time of acceleration, both beneficial adaptations (20 – page 92
forefoot striking may be more efficient mechanically, and perhaps more importantly may be needed for the increased force production coupled with a short ground contact time that is seen in faster runnin (21)- page 92
a forefoot strike allowed for more conversion of translational energy into rotational energy (22) – page 92
There are certain structural characteristics that make a person more efficient. A reduced lower leg mass in elite African runners has been hypothesized to partially explain their superiority in RE (23) – page 95
runners with shorter heels had better RE (24)- page 95
around 39% of the energy used was for forward propulsion (25) – page 95
the determining factors for VO2 were rate of ground force application and the amount of muscle mass activated (2001). Therefore these two factors combine to impact RE (26) – page 98
One training adaptation that shifts the balance of fat and carbohydrate use towards fat usage is mitochondria density (27) – page 100
RE changed when the participants did not know when they were stopping exercise, even though they ran for the same amount of time as they did during the test when they knew for how long they would be exercising (20 minutes) (28) – page 102
While distance running and even middle distance running is primarily an aerobic activity, anaerobic systems play a significant role. In the 1,500m estimates of anaerobic contribution have generally been found to be about 20%, while in the 3,000m event for men 16% anaerobic contribution was found (29) – page 105
after 8 years of training and a doubling of training volume, the percentage of ST fibers in a group of Cross-Country Skiers increased by 11% (30) – page 106
people terminate exercise at very similar temperatures of around 40 degrees Celsius. This termination of exercise happens regardless of starting temperature, precooling of the body, or rate of heat loss and storage (Gonzalez-Alonso et al., 1999). There is a theory that exercise in hot conditions, where fatigue is likely due to reaching high core body temperatures, is governed by an anticipatory regulator. This anticipatory regulation system monitors rate of heat storage and adjusts muscle activation to delay or prevent overheating. Evidence for this theory comes from studies that have studied EMG levels in a variety of temperatures. Lower EMG levels have been seen in hotter temperatures, which should not be surprising, but the anticipatory regulation can be seen in that EMG levels are lower early in the exercise when core temperatures were essentially the same (Tucker et al., 2004). Regardless of the exact mechanism, it can be seen that slowing the rate of heat storage can enhance endurance(31) – page 109
athletes had a higher pain tolerance to a wide variety of stimuli (32) – page 112
research on triathletes shows higher pain tolerance levels. In particular, high-level triathletes had higher pain tolerance when compared to active athletes, and other research shows that pain perception was related to aerobic fitness levels (33)- page 112
mental fatigue could impair performance (2009). In comparing groups who performed 90min of cognitive demanding tasks to a control group that watched documentaries, they found that the group that performed the cognitive tasks performed significantly worse on a cycle to exhaustion (34) – page 113
During the first year all skiers performed the same kind of training that consisted of high volume training with only 16% of the training being performed at or above LT. At the end of the year, subjects were split between responders, those who showed the most improvements, and non-responders. The responders trained the same way the following year, while the non-responders slightly reduced their training volume and increase the total intensity. Following the 2nd year, the non-responders showed significant improvements in race times, VO2max, and LT. The responders also showed similar continued improvements in race times. These results point to the individual nature of training adaptation and show that some subjects will thrive off of different training stimu (35) – page 129
two different groups performed either continuous exercise or interval training for 12 weeks (2002). At the end of the 12 weeks, the groups switched, so that the continuous group now did 12 weeks of interval training. It was found that the group that did continuous and then interval training improved significantly more in terms of time to exhaustion (15% to 5.3%) and VO2max (7.4% to 3.6%) than the group that did interval and then continuous training (36) – page 133
no change in VO2max when resistance training was added to cyclists training (37 – page 135
an improvement in 3k time along with an improvement in RE following plyometric training (38) – page 135
following plyometric training improved RE by 4.1%. In addition, neuromuscular factors were improved, such as decreased time to reach maximal dynamic strength and increased average power during a plyometric test (39- page 135
One study has been done on the effects of heavy weight lifting on endurance performance. Millet studied the effects of 14 weeks of heavy weight training on various parameters in triathletes. They found that RE, maximal strength, and power during a hopping test were all significantly increased (40) – page 136
periodized resistance training program resulted in the maintenance of stride length compared to a control group and a nonperiodized resistance program (41)- page 136

References

Energy system contributions in middle-distance running events., Energy system contribution to 1500- and 3000-metre track running – page 29
Fatigue-induced increase in intracortical communication between mid/anterior insular and motor cortex during cycling exercise, Limitations of physical performance in a muscle fatiguing handgrip exercise is mediated by thalamo-insular activity
Brain stimulation modulates the autonomic nervous system, ratings of perceived exertion and performance during maximal exercise
Exercise Performance is not Influenced by a 5-HT Reuptake Inhibitor
Supraspinal fatigue after normoxic and hypoxic exercise in humans, Effects of strenuous exercise on visual perception are independent of visual resolution
The independent roles of temperature and thermal perception in the control of human thermoregulatory behavior
Deception of ambient and body core temperature improves self paced cycling in hot, humid conditions
Effects of Deception on Exercise Performance
Exercise-induced diaphragmatic fatigue in healthy humans
Effects of respiratory muscle work on exercise performance
Inspiratory muscle fatigue in trained cyclists: effects of inspiratory muscle training
Inspiratory muscle training improves rowing performance, The effect of inspiratory muscle training upon maximum lactate steady-state and blood lactate concentration
Respiratory training in healthy individuals: physiological rationale and implications for exercise performance
The effect of acid-base balance on fatigue of skeletal muscle
Skeletal muscle buffering capacity and endurance performance after high-intensity training by well-trained cyclists
Limiting factors for maximum oxygen uptake and determinants of endurance performance
Effects of detraining on responses to submaximal exercise
Running economy and distance running performance of highly trained athletes
The spring-mass model and the energy cost of treadmill running., Biomechanical factors affecting running economy
Metabolic and mechanical aspects of foot landing type, forefoot and rearfoot strike, in human running
Biomechanical factors affecting running economy
Foot strike patterns and collision forces in habitually barefoot versus shod runners
Kenyan dominance in distance running
Running biomechanics: shorter heels, better economy.
Metabolic cost of generating horizontal forces during human running
The application of ground force explains the energetic cost of running backward and forward
Balance of carbohydrate and lipid utilization during exercise: the “crossover” concept
Effect of anticipation during unknown or unexpected exercise duration on ratings of perceived exertion, affect, and physiological function
Energy system contributions in middle-distance running events.
Development of aerobic power in relation to age and training in cross-country skiers
Influence of body temperature on the development of fatigue during prolonged exercise in the heat, Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment
Pain perception in athletes compared to normally active controls
Influence of aerobic fitness level on measured and estimated percieved exertion during exhausting runs
Mental fatigue impairs physical performance in humans
Responses to training in cross-country skiers
Can intermittent exercise maintain or enhance physiological benefits gained from previous traditional exercise?
Potential for strength and endurance training to amplify endurance performance
The effect of plyometric training on distance running performance.
Short-term plyometric training improves running economy in highly trained middle and long distance runners
Effects of concurrent endurance and strength training on running economy and vo2 kinetics
Running-specific, periodized strength training attenuates loss of stride length during intense endurance running