Glycolysis shows energy accounting where you invest ATP upfront and then harvest more ATP later. For one glucose, two ATP are spent in the early steps to activate the sugar, and four ATP are produced later during the payoff phase (two ATP per split product). So the net ATP yield from glycolysis itself is 2 ATP per glucose. It also generates 2 NADH, which can contribute additional ATP later in respiration depending on cellular conditions, but the direct glycolysis net is two ATP. The numbers don’t add up to four or zero, and they aren’t three because of that initial energy investment.

When stored fat is broken down, triglycerides in adipose tissue are cleaved into glycerol and free fatty acids. Glycerol is released into the bloodstream and travels to the liver where it can enter glycolysis or gluconeogenesis. The free fatty acids are carried in the blood bound to albumin and are delivered to tissues for beta-oxidation to produce acetyl-CoA and energy. Amino acids and glucose are produced from protein and carbohydrate metabolism, not directly from lipolysis, and ketone bodies are formed from acetyl-CoA mainly during prolonged fasting, not as immediate products of the fat-breaking process.

VO2 max reflects how much oxygen the body can take up, transport, and use at maximal effort. Differences between men and women come from physiology that affects oxygen delivery: men typically have larger heart size and stroke volume, higher haemoglobin levels (more oxygen carried in the blood), and more muscle mass. These factors combine to give a higher maximal cardiac output and greater oxygen delivery in men, so their absolute VO2 max is about 20% higher on average. When VO2 max is adjusted for body weight, the gap is smaller and varies with training and body composition, but the common guideline is that men are around 20% higher in absolute terms. The other options don’t fit typical physiology: there isn’t a general situation where women surpass men, nor is the difference as large as 50%.

The key idea is that OBLA (the onset of blood lactate accumulation) happens when lactate production outpaces its removal. When the body relies mainly on carbohydrate metabolism, glycolysis runs at a high rate to supply quick energy. If mitochondria can’t oxidize all the pyruvate fast enough, much of it is converted to lactate, and lactate builds up in the blood. A respiratory exchange ratio around 1.0 signals this high carbohydrate, glycolytic state, so lactate production is elevated and OBLA is more likely to occur earlier or at a lower work rate. Higher exercise intensity does push lactate up, but the specific driver here is the substrate use indicated by RER. Slow-twitch fibers are more oxidative and help clear lactate, so their predominance would delay OBLA. Faster lactate removal would also delay OBLA, not increase it.