Miles: Hey, hey, welcome back to Full Spectrum Fit. I'm Miles. Amara: And I'm Amara. Episode three, people. We're on a roll. Miles: We are on a roll. Amara, real quick, how's training been this week? Amara: Fine. I went on some walks, long ones, very intentional walks. Miles: That's the episode. You literally walked us into the episode. Amara: Oh no. Oh, no, no. Miles: Because today we are talking about Zone 2 cardio, that slow, boring, I can hold a full conversation pace that every longevity influencer won't shut up about. Amara: Chuckling. And we actually dug into the research, like real research, Miles: Mm-hmm. Amara: a 2025 sports medicine review literally titled Much Ado About Zone 2, which, yeah, that title does a lot of heavy lifting. Miles: Right? They came in spicy. The review challenges whether Zone 2 is actually optimal for mitochondrial adaptations, which, okay, that's a spicy finding when half the internet is doing slow bike rides in their living rooms. Amara: Plot twist, it gets more complicated. We dig into whether the old cardio kills gains fear actually holds Miles: Yeah, Amara: up because there's a 1980 study at the root of all that panic. Miles: 1980, the mullets were barely dry. Amara: And then we get into the real debate, HIIT versus Zone 2 for people who actually lift. Who wins when your schedule has maybe four hours a week for cardio? Miles: And we wrap with a concrete plan. Two Zone 2 sessions, one One HIIT session scheduled around leg day so you're not crawling out of the gym. Amara: Sarcastically, Miles has committed to following said plan. Miles: I have committed in writing, sort of. Amara: Okay, sure. All right, let's get into it. Personal training, check in first. Miles: Okay, so full transparency before we get into anything today. I got on a stationary bike Monday, and within about 12 minutes, I was breathing so hard, the guy next to me actually asked if I was okay. Amara: Wait, 12 minutes? Miles: 12 minutes. I lift four days a week. I move cars around at auctions. I thought I was fine, and then this bike just humbled me completely. Amara: I love that. I genuinely love that for you. Miles: Yeah, yeah, laugh it up. How was your week? Amara: Honestly, not much better. I did three solid lifting sessions, but my cardio was two walks and a lot of telling myself the walks counted. Miles: Oh, the walks count justification. Classic. Amara: They do count. Miles: Sure they do. But here's the thing, Amara. I've been hearing Zone 2 everywhere lately. every podcast, every gym bro with a smartwatch, and then I basically failed a Zone 2 session, which is supposed to be the easy one. Amara: Okay, so this is actually perfect because that's exactly what we're getting into today. Type A training put it well. Zone 2 is where your heart rate sits between 60 and 70 percent of max. You can hold a conversation. Body's mostly burning fat. Miles: Which is supposed to feel manageable, and I was not feeling manageable. Amara: No, you were feeling like a man who skips cardio. Miles: Deeply fair. And according to our health, though, Zone 2 has basically gone viral. Longevity clinics, big health podcasts, social media, it's everywhere right now. Amara: Yeah, and Jefit has been tracking how it's crossing over into actual lifting circles. Strength athletes, bodybuilders, powerlifters, people who would have laughed at slow cardio five years ago are now logging Zone 2 sessions. Miles: Which raises the question I'm genuinely curious about. If you're already training four days a week with the barbell, does adding slow, boring cardio actually do anything, or is it just something people post about? Amara: That's the whole tension, and the answer is more complicated than either side wants to admit. Miles: So, if even the guy who covers cars for a living just got wrecked by a 15-minute bike ride, maybe we should figure out what Zone 2 actually is and whether it belongs in a lifter's week. Amara: Yeah, let's find out if you need to be humiliated again or if there's a smarter way to do this. Miles: Yeah, so real quick, what even is Zone 2? Because the internet version and the actual physiology version are pretty different. Amara: Yeah, the Instagram version is just jog slowly and live forever. Miles: Exactly. So here's the actual definition. According to Type A Training, Zone 2 is exercise sitting at roughly 60 to 70% of your max heart rate, where fat is your primary fuel and blood lactate stays below about 2 millimoles per liter. Amara: The lactate part is key. Below that threshold, your body clears lactate as fast as it produces it. Cross it and things start stacking up fast. Miles: Right. And in practice, the easiest field test is the talk test. If you can speak in full sentences without gasping, you're probably there. If you're choppy, you've already drifted out. Amara: The zone 3 trap, Miles: Yeah. Amara: moderate intensity, feels like work, doesn't deliver the specific adaptations you're after. And you're too tired for your actual lifting session. Miles: I see it constantly and part of why this even got so complicated is how the concept spread and Iigo San Mayan, coach of the University of Colorado, started appearing on big podcasts. Amara: And his ideas about Zone 2 being the optimal intensity for mitochondrial development basically went everywhere. Miles: Which, look, there's real science in what he's saying, but here's where it gets good. Amara: Okay, the review. Miles: Yeah, so the 2025 narrative review published in Sports Medicine, literally titled Much Ado About Zone 2, found no strong evidence that Zone 2 is uniquely superior for mitochondrial adaptations in non-elite populations. Amara: Wait, wait, wait. The paper that Zone 2 stans are ignoring? Miles: The very one. The authors point out that recommendations for Zone 2 largely stem from observational data on elite endurance athletes who already do enormous training volumes. You can't just copy what Kipchoge does and expect the same result. Amara: And here's what the review actually says. Higher exercise intensities appear more effective for mitochondrial and cardiorespiratory improvements in the general population. That's a pretty direct challenge to the longevity. The Podcast Version Miles: It is, but-and I want to be careful here-the review isn't saying zone two is useless, it's saying the hype got ahead of the evidence. Amara: Which matters for us. Speaker 3: Right. Amara: Because Lifters asking "should I do Zone two?" deserve an honest answer, not a borrowed prescription from professional cyclists. Miles: Also, quick flag on the "two twenty minus age" formula. It tends to underestimate max heart rate in well trained people. Trained people, so if you're athletic, your Zone Two ceiling is probably higher than that math suggests. Amara: NODDING.--Talk test beats the formula every time. Miles: Every time-and now that we know what Zone What the poem actually is and what the hype got wrong, the real question for any lifter is, "OK, but will adding this kill my gains?" The physiology here is genuinely interesting. Amara: And it starts with an old fear that needs some serious updating. So here's the thing. Every lifter has heard it. Cardio kills gains. Where does that even come from? Miles: chuckling. Robert Hickson nineteen-eighty one study and it basically haunted gyms for 40 years. Amara: Right. And if it actually dug into this, the subjects in Hickson's study were doing six days of intense running and cycling on top of five days of heavy lifting. Miles: Six and five. That's 11 training days. days a week that would bury a professional athlete. Amara: Yeah, that's not a training program, that's a punishment. Miles: So if zone two three times a week isn't Hickson's protocol, why are people still scared? Amara: Because the AMPK-mTOR story sounds scary when you only hear half of it. Miles: Okay, walk me through it. Amara: So AMPK is basically your body's energy alarm system. When cellular energy drops, AMPK fires, and when AMPK fires, Where it's hard, it can suppress mTOR, which is the signal that drives muscle protein synthesis. Miles: The Circuit Breaker Amara: That's exactly it. AMPK is the circuit breaker. High-intensity cardio like sprinting or a brutal HIIT session, it's slamming that breaker. Zone 2 barely touches the switch. Miles: So the interference isn't just about doing cardio. It's about how hard. Amara: Intensity matters more than just showing up on the bike. bike. And the Wilson meta-analysis from 2012 pulled 21 studies, 422 effect sizes, confirmed it. The interference effect is both modality dependent and intensity dependent. Miles: And the modality part is huge. Running produces significantly more interference than cycling with concurrent training. Amara: So if you're doing easy zone two on the bike, you're about as far from Hickson's nightmare protocol as you... As you can get. Miles: Hmm, okay, I buy that. But here's what I actually want lifters to hear, because this part changes how I think about training. Amara: The cardiac output piece? Miles: Yes, according to G-Fit, Zone 2 improves stroke volume and cardiac output. Your heart pumps more blood per beat. Amara: And that means better oxygen delivery to muscles. Miles: Not just during conditioning, between sets. You clear lactate faster, you recover faster, you can hit. hit the next set harder. Amara: Oh, so Zone 2 is actually helping your lifts? Miles: That's the part people miss. It's not competing with your strength training. For most lifters at reasonable volumes, it's supporting it. Amara: We should have led with that instead of the molecular biology. Miles: Yeah, better recovery between sets probably converts more people than AMPK. Amara: Fair, but now flip that on its head. If Zone 2 barely activates AMPK, and doesn't strongly interfere with mTOR and HIT hammers those mitochondrial signals harder, Miles: HIT would hammer those mitochondrial signals harder. Amara: that is the question, and honestly the answer isn't as obvious as the Zone 2 hype suggests. Miles: That's where it gets interesting, because the argument for Zone 2 over HIT for lifters might not have anything to do with mitochondria at all. Amara: Okay, I need to hear that argument. Miles: Yeah, that's exactly where we're going next. So here's the honest question this whole episode has been building to: HIT clearly drives a stronger mitochondrial signal. A 2025 Frontiers in Physiology study confirmed that six weeks of HIT produced slightly superior citrate synthase improvements compared to moderate intensity continuous training. So if you're a lifter with limited cardio time, why bother with Zone 2 at all? Amara: Okay, I knew this was coming, and I'm going to push back, Miles. Miles: I figured. Amara: Because the Frontiers study also found both groups improved VO2 max. Both groups. So HIIT wins on mitochondrial markers by a margin, but here's the thing for lifters specifically. You're not just asking what builds the best engine, you're asking what can I stack on top of four days of lifting without wrecking next Tuesday's squat session. Miles: Okay, that's fair, and I hear you. But I've worked with a lot of athletes who genuinely don't have 45 minutes to ride a bike slowly. Two 20-minute HIIT sessions get more done per minute. VO2 max improvements per minute of cardio are larger above the first lactate threshold than they are in Zone 2 alone. Amara: Right, yeah, if your only goal is pure cardio adaptation and you're under four hours of cardio a week, HIIT gives you more bang per minute. I'll give you that. Miles: Wait, you're agreeing with me? Amara: On that point; but here's where I dig in: Zone Two's real argument for lifters isn't mitochondrial superiority. Miles: It's the recovery cost. Amara: Exactly-zero glycogen depletion, minimal CNS load, you can do Zone Two the day after a heavy leg session and it actually speeds clearance of metabolic byproducts without adding meaningful stress on top of what you just did. Try that with HIIT after a deadlift day. Miles: Yeah, no, that's a terrible Tuesday. Amara: Right? It's not that HIIT is bad; it's that HIIT costs something, and if your lifting is already spending most of your recovery budget, HIIT on top of that is overdraft territory. Miles: So you're saying the question isn't which one is better, but which one fits where in the week? Amara: That's it: the Broken Science Initiative did a breakdown on this; they noted that Zone Two has a low recovery cost, but Specifically because glycogen levels stay stable and AMP stays low. That's what makes it stackable with a lifting program in a way that HIIT just isn't. Miles: And honestly, the 2025 Sports Medicine Review we mentioned earlier, much ado about Zone 2, didn't crown HIIT either. It challenged Zone 2's hype, but it didn't hand HIIT the trophy. Amara: No clear winner. Science, everybody. Miles: Nobody loves that answer, but it's actually the right one here. Here, both belong in a program: HIIT when you want the cardio adaptation bang for your time-crunched buck, Zone 2 when you need to build the aerobic base without torching your recovery. Amara: With energy, the honest answer is they're not competing. They're just doing different jobs. And next, we're going to map exactly where each fits into a real lifting week. Minimum dose, best modalities, the actual structure. Miles: Yep, let's get specific. So here's the actual plan. Two zone two sessions 30 to 45 minutes each per week. That's it. That's your starting point. Amara: And the Jefit piece backs this up. Even that modest dose builds the aerobic base without torching your recovery budget for lifting. Miles: Scheduling matters though. You want those Z2 sessions the day after a leg day, not the morning before squats. Let your legs clear the soreness first. Amara: And the modality choice is actually kind of a big deal. According to guided programming research, running produced more interference with strength gains than cycling. The eccentric loading stacks on top of what your legs already took in the gym. Miles: Cycling and rowing are the move. Cycling because you can dial intensity precisely. No hills randomly spiking you out of zone two. Rowing because it's full body and concentric only. Almost no eccentric damage. Amara: Basically, no soreness tax. Miles: Exactly. Now, intensity. Forget the age-based heart rate formula. The type of training piece spells it out. 60 to 70 percent of max heart rate is the range. But the field test is way simpler. Amara: THE TALK TEST Miles: Yes; full sentences, no problem. Sing a song? Absolutely not. Gasping after one sentence, you've gone past zone two. Amara: Most lifters fail the talk test immediately because they think slow means jogging pace. It doesn't. Miles: Oh, it's embarrassingly slow the first few times. Trust me, I have personal experience with this. Amara: Speaking of personal experience, you promised you'd actually do this. Miles: Yeah, yeah, I did say that. Amara: So here's the weekly structure. Two Zone 2 sessions, 30 to 45 minutes. Then one short HIIT session, sprints, intervals, whatever gets your heart rate up fast. That covers the recovery work and the high-intensity stimulus. Miles: Without piling extra fatigue on your four lifting days, the whole thing fits cleanly around the barbell work. Amara: And this is where it gets good. You don't need to choose between... between being a lifter and having a working cardiovascular system. Miles: A revolutionary concept. Amara: Right? Okay, so, Miles, bike, rower, what are you actually doing this week? Miles: Bike, Tuesday and Thursday. Conversational pace. I will not sprint. I will not drift into Zone 2. Amara: I'll believe it when I see it. Miles: Fair. Genuinely fair. Okay, so that's a wrap on Zone 2, and honestly, I feel called out 12 minutes on a stationary bike and a stranger thought I was having a medical event. Amara: I mean, to be fair, I showed up with two walks and a lot of self-justification, so we were both starting from a very humble place. Miles: Very humble, but here's the one thing I want people to take away. If you're already lifting, Zone 2 doesn't fight your gains, it builds the engine that makes those gains stick. Stick. Amara: And the Zone 3 drift trap is real. Slow down more than you think you need to. Talk test. Bike or rower. Keep it boring. Miles: Yeah. Miles committed to actually doing it. Amara: And I remain skeptical, but hopefully convinced. Miles: That's all we can ask. All right, if you've got a fitness blind spot you want us to dig into, drop it in the reviews or tag us at Full Spectrum Fit. Amara: New episodes every Tuesday. Thanks for being here. Miles: See you next week!

Miles: Hey, hey, welcome back to Full Spectrum Fit. I'm Miles. Amara: And I'm Amara. Episode three, people. We're on a roll. Miles: We are on a roll. Amara, real quick, how's training been this week? Amara: Fine. I went on some walks, long ones, very intentional walks. Miles: That's the episode. You literally walked us into the episode. Amara: Oh no. Oh, no, no. Miles: Because today we are talking about Zone 2 cardio, that slow, boring, I can hold a full conversation pace that every longevity influencer won't shut up about. Amara: Chuckling. And we actually dug into the research, like real research, Miles: Mm-hmm. Amara: a 2025 sports medicine review literally titled Much Ado About Zone 2, which, yeah, that title does a lot of heavy lifting. Miles: Right? They came in spicy. The review challenges whether Zone 2 is actually optimal for mitochondrial adaptations, which, okay, that's a spicy finding when half the internet is doing slow bike rides in their living rooms. Amara: Plot twist, it gets more complicated. We dig into whether the old cardio kills gains fear actually holds Miles: Yeah, Amara: up because there's a 1980 study at the root of all that panic. Miles: 1980, the mullets were barely dry. Amara: And then we get into the real debate, HIIT versus Zone 2 for people who actually lift. Who wins when your schedule has maybe four hours a week for cardio? Miles: And we wrap with a concrete plan. Two Zone 2 sessions, one One HIIT session scheduled around leg day so you're not crawling out of the gym. Amara: Sarcastically, Miles has committed to following said plan. Miles: I have committed in writing, sort of. Amara: Okay, sure. All right, let's get into it. Personal training, check in first. Miles: Okay, so full transparency before we get into anything today. I got on a stationary bike Monday, and within about 12 minutes, I was breathing so hard, the guy next to me actually asked if I was okay. Amara: Wait, 12 minutes? Miles: 12 minutes. I lift four days a week. I move cars around at auctions. I thought I was fine, and then this bike just humbled me completely. Amara: I love that. I genuinely love that for you. Miles: Yeah, yeah, laugh it up. How was your week? Amara: Honestly, not much better. I did three solid lifting sessions, but my cardio was two walks and a lot of telling myself the walks counted. Miles: Oh, the walks count justification. Classic. Amara: They do count. Miles: Sure they do. But here's the thing, Amara. I've been hearing Zone 2 everywhere lately. every podcast, every gym bro with a smartwatch, and then I basically failed a Zone 2 session, which is supposed to be the easy one. Amara: Okay, so this is actually perfect because that's exactly what we're getting into today. Type A training put it well. Zone 2 is where your heart rate sits between 60 and 70 percent of max. You can hold a conversation. Body's mostly burning fat. Miles: Which is supposed to feel manageable, and I was not feeling manageable. Amara: No, you were feeling like a man who skips cardio. Miles: Deeply fair. And according to our health, though, Zone 2 has basically gone viral. Longevity clinics, big health podcasts, social media, it's everywhere right now. Amara: Yeah, and Jefit has been tracking how it's crossing over into actual lifting circles. Strength athletes, bodybuilders, powerlifters, people who would have laughed at slow cardio five years ago are now logging Zone 2 sessions. Miles: Which raises the question I'm genuinely curious about. If you're already training four days a week with the barbell, does adding slow, boring cardio actually do anything, or is it just something people post about? Amara: That's the whole tension, and the answer is more complicated than either side wants to admit. Miles: So, if even the guy who covers cars for a living just got wrecked by a 15-minute bike ride, maybe we should figure out what Zone 2 actually is and whether it belongs in a lifter's week. Amara: Yeah, let's find out if you need to be humiliated again or if there's a smarter way to do this. Miles: Yeah, so real quick, what even is Zone 2? Because the internet version and the actual physiology version are pretty different. Amara: Yeah, the Instagram version is just jog slowly and live forever. Miles: Exactly. So here's the actual definition. According to Type A Training, Zone 2 is exercise sitting at roughly 60 to 70% of your max heart rate, where fat is your primary fuel and blood lactate stays below about 2 millimoles per liter. Amara: The lactate part is key. Below that threshold, your body clears lactate as fast as it produces it. Cross it and things start stacking up fast. Miles: Right. And in practice, the easiest field test is the talk test. If you can speak in full sentences without gasping, you're probably there. If you're choppy, you've already drifted out. Amara: The zone 3 trap, Miles: Yeah. Amara: moderate intensity, feels like work, doesn't deliver the specific adaptations you're after. And you're too tired for your actual lifting session. Miles: I see it constantly and part of why this even got so complicated is how the concept spread and Iigo San Mayan, coach of the University of Colorado, started appearing on big podcasts. Amara: And his ideas about Zone 2 being the optimal intensity for mitochondrial development basically went everywhere. Miles: Which, look, there's real science in what he's saying, but here's where it gets good. Amara: Okay, the review. Miles: Yeah, so the 2025 narrative review published in Sports Medicine, literally titled Much Ado About Zone 2, found no strong evidence that Zone 2 is uniquely superior for mitochondrial adaptations in non-elite populations. Amara: Wait, wait, wait. The paper that Zone 2 stans are ignoring? Miles: The very one. The authors point out that recommendations for Zone 2 largely stem from observational data on elite endurance athletes who already do enormous training volumes. You can't just copy what Kipchoge does and expect the same result. Amara: And here's what the review actually says. Higher exercise intensities appear more effective for mitochondrial and cardiorespiratory improvements in the general population. That's a pretty direct challenge to the longevity. The Podcast Version Miles: It is, but-and I want to be careful here-the review isn't saying zone two is useless, it's saying the hype got ahead of the evidence. Amara: Which matters for us. Speaker 3: Right. Amara: Because Lifters asking "should I do Zone two?" deserve an honest answer, not a borrowed prescription from professional cyclists. Miles: Also, quick flag on the "two twenty minus age" formula. It tends to underestimate max heart rate in well trained people. Trained people, so if you're athletic, your Zone Two ceiling is probably higher than that math suggests. Amara: NODDING.--Talk test beats the formula every time. Miles: Every time-and now that we know what Zone What the poem actually is and what the hype got wrong, the real question for any lifter is, "OK, but will adding this kill my gains?" The physiology here is genuinely interesting. Amara: And it starts with an old fear that needs some serious updating. So here's the thing. Every lifter has heard it. Cardio kills gains. Where does that even come from? Miles: chuckling. Robert Hickson nineteen-eighty one study and it basically haunted gyms for 40 years. Amara: Right. And if it actually dug into this, the subjects in Hickson's study were doing six days of intense running and cycling on top of five days of heavy lifting. Miles: Six and five. That's 11 training days. days a week that would bury a professional athlete. Amara: Yeah, that's not a training program, that's a punishment. Miles: So if zone two three times a week isn't Hickson's protocol, why are people still scared? Amara: Because the AMPK-mTOR story sounds scary when you only hear half of it. Miles: Okay, walk me through it. Amara: So AMPK is basically your body's energy alarm system. When cellular energy drops, AMPK fires, and when AMPK fires, Where it's hard, it can suppress mTOR, which is the signal that drives muscle protein synthesis. Miles: The Circuit Breaker Amara: That's exactly it. AMPK is the circuit breaker. High-intensity cardio like sprinting or a brutal HIIT session, it's slamming that breaker. Zone 2 barely touches the switch. Miles: So the interference isn't just about doing cardio. It's about how hard. Amara: Intensity matters more than just showing up on the bike. bike. And the Wilson meta-analysis from 2012 pulled 21 studies, 422 effect sizes, confirmed it. The interference effect is both modality dependent and intensity dependent. Miles: And the modality part is huge. Running produces significantly more interference than cycling with concurrent training. Amara: So if you're doing easy zone two on the bike, you're about as far from Hickson's nightmare protocol as you... As you can get. Miles: Hmm, okay, I buy that. But here's what I actually want lifters to hear, because this part changes how I think about training. Amara: The cardiac output piece? Miles: Yes, according to G-Fit, Zone 2 improves stroke volume and cardiac output. Your heart pumps more blood per beat. Amara: And that means better oxygen delivery to muscles. Miles: Not just during conditioning, between sets. You clear lactate faster, you recover faster, you can hit. hit the next set harder. Amara: Oh, so Zone 2 is actually helping your lifts? Miles: That's the part people miss. It's not competing with your strength training. For most lifters at reasonable volumes, it's supporting it. Amara: We should have led with that instead of the molecular biology. Miles: Yeah, better recovery between sets probably converts more people than AMPK. Amara: Fair, but now flip that on its head. If Zone 2 barely activates AMPK, and doesn't strongly interfere with mTOR and HIT hammers those mitochondrial signals harder, Miles: HIT would hammer those mitochondrial signals harder. Amara: that is the question, and honestly the answer isn't as obvious as the Zone 2 hype suggests. Miles: That's where it gets interesting, because the argument for Zone 2 over HIT for lifters might not have anything to do with mitochondria at all. Amara: Okay, I need to hear that argument. Miles: Yeah, that's exactly where we're going next. So here's the honest question this whole episode has been building to: HIT clearly drives a stronger mitochondrial signal. A 2025 Frontiers in Physiology study confirmed that six weeks of HIT produced slightly superior citrate synthase improvements compared to moderate intensity continuous training. So if you're a lifter with limited cardio time, why bother with Zone 2 at all? Amara: Okay, I knew this was coming, and I'm going to push back, Miles. Miles: I figured. Amara: Because the Frontiers study also found both groups improved VO2 max. Both groups. So HIIT wins on mitochondrial markers by a margin, but here's the thing for lifters specifically. You're not just asking what builds the best engine, you're asking what can I stack on top of four days of lifting without wrecking next Tuesday's squat session. Miles: Okay, that's fair, and I hear you. But I've worked with a lot of athletes who genuinely don't have 45 minutes to ride a bike slowly. Two 20-minute HIIT sessions get more done per minute. VO2 max improvements per minute of cardio are larger above the first lactate threshold than they are in Zone 2 alone. Amara: Right, yeah, if your only goal is pure cardio adaptation and you're under four hours of cardio a week, HIIT gives you more bang per minute. I'll give you that. Miles: Wait, you're agreeing with me? Amara: On that point; but here's where I dig in: Zone Two's real argument for lifters isn't mitochondrial superiority. Miles: It's the recovery cost. Amara: Exactly-zero glycogen depletion, minimal CNS load, you can do Zone Two the day after a heavy leg session and it actually speeds clearance of metabolic byproducts without adding meaningful stress on top of what you just did. Try that with HIIT after a deadlift day. Miles: Yeah, no, that's a terrible Tuesday. Amara: Right? It's not that HIIT is bad; it's that HIIT costs something, and if your lifting is already spending most of your recovery budget, HIIT on top of that is overdraft territory. Miles: So you're saying the question isn't which one is better, but which one fits where in the week? Amara: That's it: the Broken Science Initiative did a breakdown on this; they noted that Zone Two has a low recovery cost, but Specifically because glycogen levels stay stable and AMP stays low. That's what makes it stackable with a lifting program in a way that HIIT just isn't. Miles: And honestly, the 2025 Sports Medicine Review we mentioned earlier, much ado about Zone 2, didn't crown HIIT either. It challenged Zone 2's hype, but it didn't hand HIIT the trophy. Amara: No clear winner. Science, everybody. Miles: Nobody loves that answer, but it's actually the right one here. Here, both belong in a program: HIIT when you want the cardio adaptation bang for your time-crunched buck, Zone 2 when you need to build the aerobic base without torching your recovery. Amara: With energy, the honest answer is they're not competing. They're just doing different jobs. And next, we're going to map exactly where each fits into a real lifting week. Minimum dose, best modalities, the actual structure. Miles: Yep, let's get specific. So here's the actual plan. Two zone two sessions 30 to 45 minutes each per week. That's it. That's your starting point. Amara: And the Jefit piece backs this up. Even that modest dose builds the aerobic base without torching your recovery budget for lifting. Miles: Scheduling matters though. You want those Z2 sessions the day after a leg day, not the morning before squats. Let your legs clear the soreness first. Amara: And the modality choice is actually kind of a big deal. According to guided programming research, running produced more interference with strength gains than cycling. The eccentric loading stacks on top of what your legs already took in the gym. Miles: Cycling and rowing are the move. Cycling because you can dial intensity precisely. No hills randomly spiking you out of zone two. Rowing because it's full body and concentric only. Almost no eccentric damage. Amara: Basically, no soreness tax. Miles: Exactly. Now, intensity. Forget the age-based heart rate formula. The type of training piece spells it out. 60 to 70 percent of max heart rate is the range. But the field test is way simpler. Amara: THE TALK TEST Miles: Yes; full sentences, no problem. Sing a song? Absolutely not. Gasping after one sentence, you've gone past zone two. Amara: Most lifters fail the talk test immediately because they think slow means jogging pace. It doesn't. Miles: Oh, it's embarrassingly slow the first few times. Trust me, I have personal experience with this. Amara: Speaking of personal experience, you promised you'd actually do this. Miles: Yeah, yeah, I did say that. Amara: So here's the weekly structure. Two Zone 2 sessions, 30 to 45 minutes. Then one short HIIT session, sprints, intervals, whatever gets your heart rate up fast. That covers the recovery work and the high-intensity stimulus. Miles: Without piling extra fatigue on your four lifting days, the whole thing fits cleanly around the barbell work. Amara: And this is where it gets good. You don't need to choose between... between being a lifter and having a working cardiovascular system. Miles: A revolutionary concept. Amara: Right? Okay, so, Miles, bike, rower, what are you actually doing this week? Miles: Bike, Tuesday and Thursday. Conversational pace. I will not sprint. I will not drift into Zone 2. Amara: I'll believe it when I see it. Miles: Fair. Genuinely fair. Okay, so that's a wrap on Zone 2, and honestly, I feel called out 12 minutes on a stationary bike and a stranger thought I was having a medical event. Amara: I mean, to be fair, I showed up with two walks and a lot of self-justification, so we were both starting from a very humble place. Miles: Very humble, but here's the one thing I want people to take away. If you're already lifting, Zone 2 doesn't fight your gains, it builds the engine that makes those gains stick. Stick. Amara: And the Zone 3 drift trap is real. Slow down more than you think you need to. Talk test. Bike or rower. Keep it boring. Miles: Yeah. Miles committed to actually doing it. Amara: And I remain skeptical, but hopefully convinced. Miles: That's all we can ask. All right, if you've got a fitness blind spot you want us to dig into, drop it in the reviews or tag us at Full Spectrum Fit. Amara: New episodes every Tuesday. Thanks for being here. Miles: See you next week!