Unit 3 Part 1

Which of the following training techniques will most likely cause the greatest caloric expenditure from excess post-exercise oxygen consumption (EPOC) following a one-hour exercise bout?

• Weight training using 60-75% 1RM

• Yoga

• Steady-state aerobic training in the fat-burning zone

• Interval aerobic training in the carbohydrate zone

Answer explanation

EPOC is commonly associated with a level of physiological disruption related to intensity and duration. Interval training allows the body to reach intensity levels that it cannot sustain for prolonged periods of time. The training technique uses a combination of anaerobic and aerobic metabolisms to reach higher intensities (carbohydrate is the primary fuel), consequently causing an increase in oxygen demand. When the oxygen demand exceeds the available amount, debt occurs. Steady state training in the “fat-burning zone” causes very little oxygen demand above what the body can deliver, limiting the metabolic disruption because the tissue is not heavily taxed. Supply generally equals demand so post-exercise debt is very limited. Although weight training can have a marked effect on EPOC when performed at high intensities with short rest intervals, low to moderate intensities with normal rest intervals do not have as dramatic an effect. Repetition ranges of 10-20 or 60-75% 1RM are often performed at higher intensities than steady state training, and the oxygen demand exceeds 100% VO2 max, but the longer rest periods commonly used in traditional weight training allow for nearly complete recovery. The very nature of interval aerobic training limits rest opportunities. Yoga may cause a very limited oxygen debt, but the nature of the activity and the measured MET levels of traditional yoga is such that the oxygen demand of the tissue is minimal. The caloric demands of traditional yoga classes are often limited compared to other forms of exercise. 

Cellular adaptations to aerobic exercise include increasing the oxidative capacity of fast twitch muscle fibers via _________________.

• increased mitochondrial density

• increased anaerobic enzymes

• increased protein concentration

• reduced reliance on intramuscular fat

Answer explanation

Cellular aerobic adaptations include the increase in the oxidative capacity of fast- twitch muscle fibers via increased mitochondrial density since the mitochondria is the organelle responsible for aerobic production of ATP. Additional muscular adaptations that enhance oxygen extraction and use include increases in mitochondrial (aerobic) enzymes, capillary density, intramuscular triglycerides, and myoglobin.

Which of the following is the primary factor responsible for an increase in muscle hypertrophy in response to resistance training?

• The concentration of anabolic hormone

• An increase in the number of muscle fibers

• The conversion of slow twitch fibers to fast twitch

• The number of sarcomeres within a myofibril

Answer explanation

Increases in muscle mass are dependent upon the concentrations of anabolic hormone that stimulate muscle remodeling and subsequent hypertrophy. Body building requires relatively high intensities, high volume, and short rest periods between sets to stimulate the anabolic hormone concentrations of testosterone and insulin-like growth factor needed for fiber hypertrophy. Increases in strength are more a factor of neural pathway efficiency, whereas increases in size are specific to the addition of protein into the myofibril. This explains why a person can gain strength without adding noticeable amounts of muscle.

The cellular organelle responsible for aerobic energy production is the ___________.

• sarcoplasmic reticulum

• actomyosin

• sarcolemma

• mitochondria

Answer explanation

The cellular organelle responsible for aerobic energy production of ATP is the mitochondria. Within the mitochondria, hydrogen molecules and their associated electrons are removed from foodstuff and transferred to oxygen molecules to produce ATP, CO2, heat, and water (all byproducts of aerobic metabolism). Increased mitochondrial density is one positive adaptation that occurs from consistent aerobic training. Called the “powerhouse” of the cell, the mitochondria takes carbohydrates, fats, and oxygen and generates ATP.

__________ is the primary fuel used to create ATP during a 3RM bench press test.

• Glucose

• Creatine Phosphate

• Acetyl-CoA

• Pyruvate

Answer explanation

Creatine phosphate is the primary source of ATP replenishment in activities lasting 5-10 seconds, such as the 3RM bench press test. Creatine kinase is the enzyme that splits creatine phosphate into a creatine molecule and a phosphate. The phosphate group is donated to ADP (ADP + P) to form ATP. After 5-10 seconds, CP stores are entirely depleted and subsequent high-intensity activity is fueled by ATP from anaerobic glycolysis. This explains why a 3RM test weight is higher than a 5 RM test weight. Switching from the breakdown of creatine phosphate to glycolysis is similar to switching from jet fuel to unleaded gasoline. 

Cardiac output x (a-v)O2 difference represents _________, which determines the caloric cost of the exercise.

• oxygen consumption (VO2)

• blood pressure

• rate-pressure product

• myocardial demand

Answer explanation

Cardiac output multiplied by the difference between the arterial and venous oxygen content is called oxygen consumption, or VO2.  Cardiac output represents the oxygen delivery of the heart and is the product of the rate at which the heart beats (heart rate) and the volume of blood ejected with each beat (stroke volume) per minute. Similarly, the oxygen consumed by cells in the body is measured via the difference between oxygen coming from the left side of the heart (arterial oxygen concentration) and the amount of oxygen left in the deoxygenated blood being returned to the right side of the heart via the venous system (also referred to as venous oxygen saturation). This difference is referred to as the (a-v)O2 difference. Overall, the oxygen consumed is a product of oxygen delivery (cardiac output) and utilization (a-v)O2 difference. Total O2 utilization can then be converted to give an approximate estimation of kcal expenditure (≈5 kcal per L O2). As one trains aerobically, cardiac output and oxygen extraction increase in capacity, making it possible to burn more calories per minute. This explains why a person in shape can easily burn more calories per minute than someone who is sedentary.

Although all energy systems are used to various extents, intense activities that last 30-45 seconds will predominantly rely on _________ for energy production.

• phosphagen (ATP-CP)

• anaerobic glycolysis

• fat oxidation

• aerobic glycolysis

Answer explanation

 Although energy is supplied by multiple energy systems, activities that cause fatigue within 30-45 seconds will use anaerobic glycolysis as the primary energy source. These activities involve the recruitment of fast motor units that favor the utilization of glycogen to re-synthesize ATP. Anaerobic glycolysis uses glycogen stores in the muscle and liver to generate ATP.

Which of the following is the contractile unit of a skeletal muscle that runs in sequence along the myofibril?

• Sarcoplasmic reticulum

• Fascicule

• Sarcomere

• Actomyosin

Answer explanation

The sarcomere is the contractile unit of a skeletal muscle; it contains actin and myosin filaments as well as structural proteins involved with tension development. Sarcomeres are aligned in a series and attached via Z disks along the myofibril of a muscle cell. Muscle size and force production capabilities are dependent upon these contractile units which also represent the site of muscle remodeling

The _________ is the first system of the body to adapt to exercise.

• muscular system

• nervous system

• endocrine system

• cardiovascular system

Answer explanation

The nervous system is the first system to adapt to exercise. The collective system works to enhance movement efficiency by controlling muscle tension and force outputs. The motor nerve is the first to adapt to resistance training as scientific evidence suggests most initial strength improvements are neural in nature. It can take the body approximately 6-8 weeks for protein synthesis to occur. 

The voluntary action of muscle is controlled by signals from the nervous system called _________.

• action potentials

• motor signals

• voluntary impulses

• dynamic reflexes

Answer explanation

Action potentials are nervous signals that initiate the release of calcium from the sarcoplasmic reticulum (SR). The action potential travels from the motor neuron down the T-tubules to the SR where calcium is released. When the action potential is removed, calcium returns to the SR and the contraction is stopped.