Human physiological adaptations during endurance training

Question 1

What is exercise?

Answer 1

Activity requiring physical effort, carried out to sustain or improve health and fitness: exercise improves your heart and lung power.

Question 2

What is the most recent change in homo sapiens morphology?

Answer 2

Most recent change in homo sapiens is our highly encephalized brain (higher relative brain size)

Question 3

What are earlier morphological adaptations that occurred between 1-2 million years ago, at the earliest homo erectus?

Answer 3

Larger brain and body
Substantially reduced face and teeth
Increased intraspecific body size variation

Question 4

When did the mode of locomotion of humans change in history?

Answer 4

Homo Erectus (~2 million years ago) was the first ancestor that had strong bipedality (mostly bipedal)

Ardipithecus (~4.5 million years ago) also started to be more upright in their locomotion

Sahelanthropus (~7 million years ago) also have fossils that demonstrate they could walk on two legs

Question 5

What change in the environment could have led to bipedalism in humans?

Answer 5

Major faunal change between 8 and 7 Ma are probably linked to the growth of the Arctic Ice Sheet, which impacted global climate patterns. This event may have led to the borealization (adaptations to northern regions) of much of mid-latitude Eurasia and the onset of desertic conditions in Africa.
The vegetational changes include the development of large areas of grasslands and woodlands.
Early hominids initially remained faithful to their largely frugivorous diet (i.e. their teeth did not change much), but they developed a new way of getting between food resources - bipedalism, whereas most mammal lineages merely changed their diet as the vegetation changed around them (and barely altered their locomotor repertoires). This is why the study of locomotion is so important for understanding hominid origins.

Question 6

Describe the difference between walking and running

Answer 6

• Walking –> pendulum
• Running –> Mass-spring
Those are very different types of modes of locomotion

Question 7

How is the cost of transport expressed (in units)?

Answer 7

CoT is generally expressed as the amount of energy spent above resting to transport 1 kg body mass (Mb) over a distance of 1m
mL O2 /kg/km

Question 8

Does speed impact the metabolic CoT?

Answer 8

In humans, CoT is independent of speed, at least for speeds ranging from 2.2 m/s (8 km/h) to about 5 m/s (18 km/h) wherein the air resistance is negligible.
In horses, yes

Question 9

How does human’s CoT for speed compare to horses’?

Answer 9

the cost of transport for horses, regardless of their speed, is much lower than humans.
- Even when walking, humans’ CoT is higher although the difference is not as big as when we are running (compared to horses)

Question 10

How do humans and horses compare in terms of sprint range? Endurance running range?

Answer 10

Human sprint range is lower than in horses, as humans can go to max about 10 m/s, and horses, up to 20 m/s
However, Human ER range (Endurance Running range) can be higher in humans as compared to horses. Trained athletes (elite) can sustain higher speeds of running for long periods of time

Question 11

At which speed will humans naturally start running as opposed to walking? Why?

Answer 11

Most humans will start running when reaching a speed of ~2.2 m/s because metabolic cost of transport is more efficient when running at this speed (vs. walking). The stored elastic energy can be used whereas it is not used as you walk.

Question 12

Name a few mammals who have good endurance for running.

Answer 12

Humans (but not other primates*)
Social carnivores (hyenas, some dogs like huskies!)
Migratory ungulates (wildebeest, horses).

Question 13

Which types of energies are involved in walking vs running&

Answer 13

Walking: Transfer of kinetic energy (movement) to potential energy (position). You are completely transferring your weight from one leg to the other.
Running: Kinetic + potential + elastic. Your leading foot hits the floor (high kinetic energy; lower potential energy and increase in elastic energy (in tendons of legs in particular))
Elastic energy will be released as you move from middle stance to toe off (pushing away) as you run.
This permits the use of another type of energy that wasn’t needed when walking, but that requires adaptations.

Question 14

How can muscles and tendons favorize running and which specific ones are most important?

Answer 14

Muscle and tendons can store energy that is released during the middle stance to toe-off phase of running. Can save 50% of the metabolic cost of running.

• The Achilles tendon is the most important followed by the iliotibial band.
• The plantar arch can restore 17% of the energy in the middle stance to toe-off phase of running.

Question 15

What morphologic features of humans favorize running speed/endurance?

Answer 15

• Relative to body weight, humans have the long legs, leading to longer stride.
• The legs also feature compact feet and toes (9% in humans versus 14% of body weight in chimpanzees)

Question 16

How does the stress caused by running impact bones in humans?

Answer 16

Running poses a stress on the skeleton. At high speeds, peak ground reaction force may reach 3-4x BW. Some of this energy is stored, but some has to be dissipated –> Lower limb joint enlargement. This can help spread and dissipate stressful forces over a larger area.

Question 17

Explain how the body stabilizes the head when walking/running

Answer 17

When walking, there is not really a need for stabilizing the head because the contact with the ground is used to keep you going straight.
When running, our trunk twists (counter-rotates) –>
We can rotate at 2 levels, at our head and hips.
• Head: The nuchal ligament, present in other mammals who can run (but not non-human primates) helps stabilizing the head. In our evolution, this was important for hunting or fleeing, for example.
• Narrow waist, permissible because of smaller intestines due to an energy dense diet, allows for greater counter-rotation of the trunk. (vs. other primates have much larger intestines).
• The greatly enlarged gluteus maximus, a distinctive feature of humans, is a muscle recruited during running but not walking on a level surface. It is important for trunk stabilization, spear throwing or pitching. It is useful when going up in mountains.

Question 18

Name 4 human adaptations for thermoregulation.

Answer 18

1• Bipedalism and narrow elongated body form
o Decrease of body surface exposed to solar radiation (by 60%)
o Increased potential for cooling by convection, by exposing a greater proportion of the body to a cooler microclimate (i.e., higher above the ground, more exposed to air movement, such as the wind).

2• Reduced body hair
o Hair traps air, which can be heated.
o Hair also decreases the efficacy of sweating
o However, light-colored fur of typical desert animals reflects radiation heat, reducing its impact up to 70% (most of these animals are on 4 legs and their back is well exposed to the sun).

3• Mouth breathing
o Unloads heat through air expired. Animals have panting, which is also an effective means of cooling their bodies. However, contrary to breathing in humans, which can be decoupled from stride rate (we can take 1,2,3 or more breaths during a stride), panting is limited to once per stride.

4• Sweating
o Humans sweat twice as much as camels and 4x as much as horses. Humans regulate sweating in relation to water availability.

Question 19

How did endurance running impact our morphology as humans, in terms of thermoregulation?

Answer 19

• Dark skin pigments blocks sunlight in tropical open grasslands
• Tall, narrow form helps cool down the body
• Eccrine sweating with reduced body hair dissipates heat via evaporation
• Scalp hair blocks sunlight
• Tightly coiled hair impedes UV radiation
• Expanded venous circulation in the braincase cools the head via countercurrent heat exchange

Question 20

How did endurance running impact our morphology as humans, in terms of head stabilization?

Answer 20

• Enlarged semicircular canals (posterior and anterior) increase the sense of balance
• Improved vestibulo-ocular reflexes adjust eye movements to stabilize images
• Short snout & neck ligaments stabilizes the head

Question 21

How did endurance running impact our morphology as humans, in terms of body stabilization?

Answer 21

• Loosen, low, wide shoulders with decoupled head help swinging of upper body to counter leg movement
• Shorter arms reduce effort in arm-swinging
• Tall, narrow waist allow for greater counter-rotation of the trunk
• Larger back & buttock muscles, stabilized spine-hip joint stabilize the trunk

Question 22

How did endurance running impact our morphology as humans, in terms of skeletal strength?

Answer 22

• Expanded joint surfaces in lower body (spine, hips, legs) reduce stress in the skeleton
• Shorter femoral necks (reduce bending stress)
• Larger heel bones absorb shock

Question 23

How did endurance running impact our morphology as humans, in terms of respiration?

Answer 23

• More mouth breathing allows more efficient ventilation

Question 24

How did endurance running impact our morphology as humans, in terms of energetics?

Answer 24

• Larger thyroid and adrenal glands allow more efficient utilization of energy stores (CHO, fats)
• longer legs and lighter feet (increase stride length with low stride rate, reduce energetic cost)
• Shorter toes decrease mechanical work
• inward, projected big toe and compacted mid-foot restrict the rotation of feet
• Tendons and ligaments in legs acts as springs to store and release elastic energy
• Well-developped achilles tendon
• Foot arches act as springs to store elastic energy and absorb shock.

Question 25

Define endurance.

Answer 25

The ability to endure an unpleasant or difficult process or situation without giving way.

Question 26

Which compound increases after exercise in humans and in dogs?

Answer 26

endocannabinoids

Question 27

What is the mechanism of endocannabinoids to lead to “runner’s high” ?

Answer 27

A. Hedonic signals acting on the mesolimbic dopamine system
1- Activation of the endocannabinoid receptor 1 (eCB1) relieves the inhibition of GABAergic neurons
2- This loss of inhibition results in dopamine release in the nucleus accumbens region (reward system)

B. Analgesics (exercise-induced analgesia)
1- Analgesia occurs in both the CNS and PNS via eCB receptors expressed on peripheral nerve fibers

Question 28

Which responses do humans have to water immersion?

Answer 28

Humans, like other diving mammals, have a diving response induced by apnea and cold-water facial immersion. Physiological effects of this response include:

• Bradycardia, which lowers oxygen consumption
• Peripheral vasoconstriction, which selectively redistributes blood flow to the organs most sensitive to hypoxia
• Contraction of the spleen, which injects a supply of oxygenated red blood cells into the circulatory system. A single contraction expels RBCs, causing a hemoglobin increase that corresponds to a 2.8-9.6% increase in oxygen content.

Question 29

Which species show the greatest HR reductions in water? Where do humans lie?

Answer 29

a number of species showed the greatest reductions in HR (70-90%) were found in marine mammals, such as dolphins and seals
Interestingly, an intermediate group existed with approximately 50% reduction of HR, and this contained beavers, muskrats, manatees and trained human divers.

Question 30

Which gene is different between two sea nomads populations living 25 km apart, one being more land-based, the other being more diving sea nomads?

Answer 30

One of the gene identified being different between the two was the PDE10A which is associated with spleen size

Question 31

Which two cultural revolutions have drastically changed the relation between our bodies and the environment?

Answer 31

• The agricultural revolution

- The industrial revolution

Question 32

What was the impact of the agricultural revolution on the relation between our bodies and the environment?

Answer 32

• We went from nomadic to sedentary
• Decrease in food variety
• Transformation of our society between scavenging and agricultural ways of living. Changed from foods that required a lot of mastication and nutrient-poor. Now we have teeth problems because our food is too easy to masticate

Question 33

What was the impact of the industrial revolution on the relation between our bodies and the environment?

Answer 33

• Transportation, less movement
• Increased processed foods.
• Effects of pollution
• Working time, repetitive tasks, sitting jobs, factory work

Question 34

How does sedentarity predict disease independently of weight?

Answer 34

Physical inactivity –> Loss of muscle mass and abdominal adiposity –> Macrophage infiltration of visceral adipose tissues –> chronic systemic inflammation –> Insulin resistance, atherosclerosis, tumour growth, impaired bone formation –> T2DM, CVD, Ca, Osteoporosis