Test 2 (Paper)

Question 1

Define VO2max

Answer 1

The fastest rate at which the body can utilize o2 during heavy exercise

Question 2

How much energy do working skeletal muscle cells account for during severe exercise?

Answer 2

90%

Question 3

What has heat stress previously been shown to do?

Answer 3

Suppress Vo2max and work capacity

Question 4

What was the aim of the study?

Answer 4

Identify the primary factor that limits Vo2max and determine the mechanisms underlying the blunted Vo2max and early fatigue associated with head stress

Question 5

What was the subjects age?

Answer 5

24 years ± 4

Question 6

What was the subjects Maximal heart rates?

Answer 6

191 bpm ± 6

Question 7

What was the subjects Vo2max?

Answer 7

4.7 L/min ± 0.5

Question 8

Catheters were placed where 2 hours prior to the experiment?

Answer 8

• Femoral artery
• Bilateral femoral veins
• Antecubital forearm vein

(Using the Seldinger technique under local anesthesia)

Question 9

Explain the Proceeder the participants underwent?

Answer 9

Completed 3 cycle exercise tests in the upright postivtion

Started with either high or normal skin and core temperatures (+1 and +10 respectively)

In test 1 and 3 they cycled until volintional fatigue whereas in test 2 they cycled for the same duration as in heat stress

In every test power output was held at 356±14 W

Each test was separated by an hours rest

Question 10

How were bodily fluids restored?

Answer 10

Subjects ingested
2 L of a carbohydrate-electrolyte solution
during resting periods

Question 11

How were internal and skin temperatures elevated?

Answer 11

By perfusion of hot water (44°C) into a jacket in contact with the skin of trunk and arms while the subject was wearing rain trousers during the light cycling

Question 12

When was the muscle biopsy taken and from where?

Answer 12

During the resting period before each intense exercise bout, a muscle biopsy from the vastus lateralis was obtained

Question 13

Vo2max was significantly diminished in heat compared to normal but by how much?

Answer 13

4.28±0.15 versus 4.72±0.18 L/min

Question 14

What happened when subjects exercised for the same duration in hot as in normal conditions (5.5±0.2 mins)?

Answer 14

Muscle lactate accumulation, PCr hydrolysis, and ATP hydrolysis were greater, and the rate of leg lactate release tended to be higher

Question 15

What were the three main findings?

Answer 15

1. Heat caused drastic declines in Vo2max
   (decline of maximal cardiac output and mean arterial blood pressure)
2. Decline skeletal muscle Vo2 before fatigue
   (lowering systemic and skeletal muscle O2 delivery)
3. Enhanced muscle lactate accumulation

Question 16

What do the findings suggest?

Answer 16

That impaired skeletal muscles aerobic energy provision and work capacity during maximal aerobic exercise are directly related to the inability of the heart to maintain maximal cardiac output and O2 delivery to locomotive skeletal muscles

Question 17

What happened to maximal cardiac output and blood flow to the legs when heat stress was added?

Answer 17

Maximal cardiac output increases (1.5 L/min)

Blood flow to the legs lowered (0.7 to 2.7 L/min)

Question 18

When the heat stress caused the lower leg blood flow how was Vo2 in the legs still able to be maintained?

Answer 18

Elevations in CaO2, arteriovenous o2 difference and o2 extraction

Question 19

Why was leg vascular conductance unchanged throughout exercise?

Answer 19

Blood flow to the legs paralleled those of mean arterial blood pressure

Question 20

What allowed the maintenance of arterial O2 content

during exercise?

Answer 20

Decline in arterial
O2 saturation

Decline in PO2 saturation

Increase in hemoglobin concentration

Question 21

What happened to leg o2 extraction and 2-legged Vo2 and how much did they increase/decrease?

Answer 21

Leg o2 extraction increased progressively by up to 91%

2-legged o2 extraction decreased by 0.2 L/min

Question 22

What caused the expected 3- to 5-fold

elevation in skin blood?

Answer 22

Diminished splanchnic and renal blood flow

Question 23

What happened to leg vascular conductance and why?

Answer 23

Didn’t change suggesting that lowering in blood flow to the legs and o2 transport was due to the reduction in maximal cardiac output and perfusion pressure

Question 24

What does femoral venous blood reflect?

Answer 24

Femoral venous blood reflects mixed blood from all leg
tissues (skin, bone, connective tissue, and fat account for 20%
of the 12.1 kg of leg in these subjects), including muscles
with presumably different levels of activation, metabolism,
and O2 extraction during exercise.

Question 25

What caused the decline in stroke volume?

Answer 25

Drop in maximal cardiac output

1.5 to 2.9 L/min

Question 26

What was the cause of the impaired stroke volume with heat stress?

Answer 26

The reduction in central blood volume and cardiac filling secondary
to the increased skin blood flow and volume

Question 27

How does heat stress reduce Vo2max?

Answer 27

By accelerating the declines in maximal cardiac output and mean arterial blood pressure

(This leads to decrements in locomotive skeletal muscles blood flow, O2 delivery and O2 uptake)

Question 28

Collectively what to the findings suggest?

Answer 28

Suppressed systemic and locomotive skeletal muscle aerobic
capacity that precedes fatigue with and without heat stress in
trained subjects is closely related to the inability of the heart
to maintain maximal cardiac output and
O2 delivery to locomotive muscle.

Question 29

Time to fatigue significantly diminished in heat compared to normal but by how much?

Answer 29

5.45±0.23 versus 7.63±0.42 mins