KIN 202 M2 Module 5

What is a graded exercise test (GXT), and what is its purpose?

A GXT is a protocol with a systematic, incremental increase in exercise intensity over time until the participant can no longer maintain the workload. It assesses cardiovascular, respiratory, and muscular endurance capacity.

Why does the step model differ physiologically from the ramp model in a GXT?

The step model uses steady intensity stages, allowing partial recovery, while the ramp model continuously increases intensity—producing smoother VO₂ and HR data but less recovery, often leading to quicker fatigue.

What are the physiological and graphical definitions of VO₂ max?

• Physiological: The maximum capacity of the cardiovascular and respiratory systems to deliver and utilize O₂ for ATP production.

• Graphical: The plateau in VO₂ despite increasing workload (≤150 mL/min rise).

Why is VO₂ max sometimes not achieved, and what does this tell you about test validity?

Many individuals don’t show a plateau (<20% of tests). Instead, VO₂ peak may be used. Factors include motivation, muscle fatigue, or protocol design (e.g., increments too steep or too short).

List secondary indicators of a successful VO₂ max test.

• Volitional fatigue (cannot maintain cadence/pedal pace)

• HR ≥ age-predicted max (220 – age or 208 – 0.7×age)

• RER ≥ 1.15

• RPE ≥ 17/20

• High blood lactate (variable)

Why might RER > 1.15 be considered an indicator of maximal effort?

Because high CO₂ output relative to O₂ consumption reflects buffering of lactic acid—showing reliance on anaerobic metabolism.

Why is VO₂ max typically higher on a treadmill than on a bike?

Running activates more total muscle mass (legs + arms), is weight-bearing, and leads to higher cardiac output (Q), larger (a–v)O₂ difference, and greater vascular conductance.

How does posture influence VO₂ max between treadmill and cycling tests?

Upright, weight-bearing posture in treadmill running enhances venous return and muscle engagement, increasing O₂ delivery capacity.

What happens to muscle activation and O₂ demand as work rate increases during a step GXT?

Increased work rate requires more force generation → higher motor unit recruitment and AP frequency → more ATP and O₂ demand.

Why does EMG activity increase with higher workloads, and what does it reveal about neuromuscular function?

EMG amplitude rises because more motor units are activated and firing more rapidly to meet greater force demands—showing increased neural drive and fatigue development.

What is the crossover concept?

The point during progressive exercise where carbohydrate oxidation surpasses fat oxidation as the primary energy source.

Why does the crossover from fat to carbohydrate metabolism occur as intensity increases?

1. Type II fiber recruitment (glycolytic, low mitochondrial density).

2. Increased epinephrine stimulates glycogenolysis.

3. Elevated lactate & H⁺ inhibit lipase, reducing fat use.

4. Reduced blood flow to adipose tissue limits FFA delivery.

Define lactate threshold (LT) and onset of blood lactate accumulation (OBLA).

• LT: The intensity where lactate starts to rise exponentially.

• OBLA: The work rate at which lactate reaches 4 mmol/L.

Why do more aerobically fit individuals have a higher lactate threshold?

They have greater mitochondrial density, capillarization, and lactate clearance—allowing them to sustain higher workloads before lactate accumulation.

What determines blood lactate concentration during progressive exercise?

he balance between rate of lactate appearance (Ra) from skeletal muscle and rate of disappearance (Rd) by oxidative tissues (liver, heart, Type I fibers).

Why does lactate accumulate at higher intensities?

Because Ra > Rd—Type II fibers produce lactate faster than it can be cleared or oxidized by Type I fibers and other organs.

Describe what happens to energy systems as intensity increases from low to high.

• Low intensity: Aerobic metabolism dominates; lactate low and steady.

• Moderate: Aerobic can’t meet O₂ demand → lactate rises (LT).

• High: Anaerobic metabolism predominates → lactate rapidly accumulates (OBLA).

Why does anaerobic metabolism dominate at high intensities despite being less efficient?

ATP demand exceeds O₂ delivery/utilization capacity, so the body relies on faster anaerobic glycolysis even though it produces lactate and fatigue.