Angela Naeth racing on a time trial bike

Working Theory 08 · Training Science

Will Heavy Lifting Make You Bulky and Slow?

The short answer

Heavy lifting does not inevitably make endurance athletes bulky or slow. In these studies it improved selected economy and performance measures, and one small runner trial detected no significant body-weight change. Muscle growth is still possible. Here is what the research shows, where it stops, and how we build strength into your season at Angela Naeth Coaching.

By Angela Naeth · November 2026 · 8 min read

Working Theory takes a popular training claim, checks it against the actual research, and tells you what to do about it. No trends, no dogma, just the reasoning behind how we coach.

The Claim

“If I lift heavy, I'll get bulky and slow. Endurance athletes should stick to light weights and high reps.”

November is when strength comes back into the conversation. For many of you the racing is done for the year, the hours have dropped, and there is room in the week. It is also when this belief shows up. Heavy weights are for lifters. Endurance athletes should keep the load light, do lots of reps, and stay away from anything that could add weight.

I understand the worry. Nobody wants to carry extra mass up a climb or through the last miles of a marathon. I look at this as a physical therapist by training, a former Division I track athlete, and someone still racing as a professional triathlete and gravel cyclist. What I care about is what strength work does to your running and riding. The research gives a useful answer, with limits worth knowing.

What the research says

A note on the evidence before we start. This article draws on seven papers: three small training studies and four reviews. The reviews overlap with some of the same primary trials, and six of the seven were published before 2020. Read them as one body of evidence, not seven independent confirmations.

Open any research note below for the full study detail. The headline is the takeaway.

Heavy squats improved running economy, with no significant body-weight change detected.

In one small study, eight well-trained runners who added heavy half squats for eight weeks improved running economy by 5%, with no significant body-weight change detected.

Bar chart of percent change in the strength group after eight weeks of heavy half squats: half-squat one-repetition maximum up 33.2%, rate of force development up 26.0%, laboratory time to exhaustion at maximal aerobic speed up 21.3%, running economy at 70% VO2max improved 5.0%. VO2max and body weight are labeled no significant change reported, with no bar plotted. — Støren et al. 2008. 17 runners: 8 lifted, 9 controls. Controls showed no significant changes. Laboratory outcomes, not race times.

Støren 2008: eight well-trained runners added heavy half squats for eight weeks and improved running economy by 5%, with no significant body-weight change detected.

Støren and colleagues randomly assigned 17 well-trained runners to two groups [1]. Eight, four men and four women, added four sets of four-repetition-maximum half squats three times weekly for eight weeks to their usual endurance training. Nine continued endurance training alone.

The strength group improved half-squat one-repetition maximum by 33.2%, rate of force development by 26.0%, running economy measured at 70% VO₂max by 5.0%, and laboratory time to exhaustion at maximal aerobic speed by 21.3%. That last number is a laboratory test, not a 21.3% faster race. The researchers detected no significant change in VO₂max or body weight in the strength group, and no significant changes in the measured outcomes in controls. It is a small study, so read it as one data point.

Blagrove 2018: in 24 studies, running economy often improved by about 2% to 8%. Body-composition measures were usually unchanged, with exceptions.

Blagrove and colleagues reviewed 24 studies of strength training and distance-running outcomes, including studies in triathletes and duathletes [2]. Among the 20 studies measuring running economy, improvements of about 2% to 8% relative to running-only controls were commonly reported, but not consistently. Time-trial performance over 1.5 to 10 km also tended to improve, although results were not uniform. VO₂max and body-composition measures were usually unchanged in this review. Some studies did report increased body or lean mass, and unchanged total body weight does not rule out growth in individual muscles.

High-load training has clearer support for running economy.

A 2024 review found a significant average running-economy benefit from high loads, but did not detect a significant improvement with loads of 40% to 79% of one-repetition maximum. That does not prove those methods are useless.

Forest plot of published signed effect sizes for running economy, where negative favors strength training: high load -0.266, 95% CI -0.516 to -0.015; combined methods with outliers removed -0.426, 95% CI -0.768 to -0.083; plyometric across all speeds -0.122, CI -0.299 to 0.054, not significant; submaximal load of 40 to 79% 1RM -0.365, CI -0.875 to 0.146, not significant; isometric -0.269, CI -0.790 to 0.252, not significant. — Llanos-Lagos et al. 2024. Dots are published signed effect sizes; lines are 95% confidence intervals; negative favors strength training. ns means not statistically significant, which is not proof of no benefit. Different analyses versus controls, which could include low-load training; these are not head-to-head estimates of which method is best. The slower-speed plyometric subgroup is not plotted because its published confidence interval and p value disagree.

Llanos-Lagos 2024: high-load training has clearer support for running economy. No significant benefit was detected for 40% to 79% 1RM, which does not prove those methods are ineffective.

This is the part of the claim that matters most for how you lift. A 2024 meta-analysis by Llanos-Lagos and colleagues pooled strength-training studies in middle- and long-distance runners [3]. High-load training, at least 80% of one-repetition maximum, produced a small average improvement in running economy. Combined methods produced a moderate improvement after outlier removal. Plyometric benefits were found in the slower-speed subgroup, not across all speeds.

Running economy is an energy cost, so in the published numbers a negative effect size favors strength training. High load was -0.266 (95% CI -0.516 to -0.015). Combined methods, with outliers removed, were -0.426 (95% CI -0.768 to -0.083). Across all speeds, the plyometric estimate was -0.122 (95% CI -0.299 to 0.054), which was not statistically significant.

The review did not detect statistically significant running-economy improvements versus controls for submaximal loads of 40% to 79% 1RM or for isometric training. Those null results do not establish that these methods cannot help. It is also worth knowing what that category means. In this review, submaximal means 40% to 79% of one-repetition maximum. That is a load band, not a description of light weights or high repetitions, and the comparison groups could themselves include low-load work below 40%. In the review's moderator analyses, larger high-load benefits were associated with faster assessment speeds and higher VO₂max.

Strength showed up after a long laboratory ride.

In trained cyclists, adding heavy strength work improved power at the end of a long laboratory ride, and in well-trained women it also improved 40-minute power and cycling economy. That is laboratory performance, not a measured race finish.

Bar chart: in the strength group of 11 well-trained men, mean five-minute all-out power after 185 minutes of laboratory cycling rose from 371 watts before training to 400 watts after 12 weeks; the 9 controls showed no significant change. — Rønnestad et al. 2011. Bars are group means for the strength group (11 well-trained men). Controls (7 men, 2 women) showed no significant change. Protocol: 185 minutes at 44% of maximal aerobic power, then a five-minute all-out test. After training, oxygen use, heart rate, blood lactate and perceived exertion in the final hour fell more than in controls. Laboratory protocol, not a race outcome.

Rønnestad 2011: after 12 weeks, 5-minute all-out power after 185 minutes of laboratory cycling rose from 371 to 400 watts in the strength group. Controls showed no significant change.

Twenty well-trained cyclists completed 12 weeks of usual endurance training, with 11 men also doing four lower-body strength exercises, three sets of 4 to 10 repetition maximum, twice weekly [4]. The nine controls included seven men and two women. The abstract describes the groups as assigned; it does not describe random assignment.

Before and after training, they completed a laboratory test of 185 minutes at 44% of maximal aerobic power followed by a five-minute all-out effort. After training, oxygen consumption, heart rate, blood lactate and perceived exertion during the final hour were reduced more in the strength group than in controls. Mean power in the five-minute test after prolonged cycling rose from 371 to 400 watts in the strength group; controls showed no significant change. That is power at the end of a long laboratory ride, not a measured race finish.

Vikmoen 2016: in well-trained female cyclists, heavy strength training improved 40-minute power, economy and fractional utilization. Thigh muscle did grow, and those changes were correlated with performance, not proven as the cause.

In a separate 11-week randomized study of 19 well-trained female cyclists, adding heavy strength training improved 40-minute all-out mean power, fractional utilization of VO₂max and cycling economy [5]. The thigh muscle did grow. Quadriceps cross-sectional area increased more in the strength group. Greater performance improvements were correlated with larger gains in quadriceps size (r=0.73) and reductions in the proportion of type IIAX-IIX fibers (r=-0.63), alongside a shift toward type IIA fibers. These correlations do not prove that either change caused the performance gain.

Rønnestad and Mujika 2014: heavy or explosive strength work can improve running economy, with heavy work best supported for cycling economy. Lactate-threshold findings were mixed, and lactate threshold is not Critical Power or Critical Speed.

A 2014 review concluded that adding heavy or explosive strength work to endurance training can improve running economy, with heavy strength work best supported for cycling economy [6]. Some studies improved speed or power at VO₂max, or time to exhaustion at those intensities; lactate-threshold results were mixed. Lactate threshold is not the same measure as Critical Power or Critical Speed, so this review does not tell us how strength affects those.

Separate injury research found lower risk with strength-category programs.

Strength-category programs were tied to about 69% lower relative injury risk in the studies that were pooled. Those were mainly team-sport and military settings, not an endurance guarantee.

Risk ratio chart versus study controls, below 1 favors intervention: strength-category programs from 4 studies 0.315, 95% CI 0.207 to 0.480; proprioception 0.550; multiple program types 0.655; stretching 0.963, CI 0.846 to 1.095, not statistically significant. Mainly team-sport and military populations. — Lauersen et al. 2014, 25 trials, risk ratios (RR) with 95% confidence intervals. Below 1 favors intervention; relative, not absolute, risk. ns means not statistically significant. The strength category came from 3 soccer studies and 1 military-recruit study. Strength-category programs were not specifically heavy lifting for endurance athletes.

Lauersen 2014: strength-category programs had about 69% lower relative injury risk in mainly team-sport and military settings, not an endurance-sport guarantee.

Lauersen and colleagues analyzed 25 randomized trials involving 26,610 participants and 3,464 injuries [7]. Across four studies classified as strength training, the pooled injury risk ratio was 0.315 (95% CI 0.207 to 0.480), about 69% lower relative risk in those settings. Stretching alone did not show a statistically significant preventive effect (RR 0.963, 95% CI 0.846 to 1.095). These estimates do not establish the same reduction for endurance athletes.

Across six studies reporting overuse injuries, mainly multicomponent programs, pooled relative risk was about 47% lower (RR 0.527, 95% CI 0.373 to 0.746). This was not a strength-only estimate. The review mainly covered team-sport and military-training settings, not endurance-specific heavy-strength programs. Its strength-category estimate came from three soccer studies and one military-recruit study. Strength-based prevention programs reduced injury risk in some studied populations; the exact benefit for endurance athletes is less certain.

In one paragraph

In these studies, adding heavy strength training improved selected measures of running or cycling economy and performance, including power after prolonged laboratory cycling. One small runner trial found no significant body-weight change, while the runner review found body-composition measures usually unchanged, with exceptions. Some local muscle growth can occur. The 2024 review found a significant average running-economy benefit from high loads but not from submaximal loads; that does not prove submaximal training is ineffective. Separate injury-prevention trials in mainly team-sport and military settings found lower injury risk with strength-category programs. At ANC, that is why strength sits in your foundation and why the load progresses through your season.

What this means for your training

The research tells you that strength can help. It does not tell you how to fit it around swimming, riding and running in a real week. Here is how we do it at ANC, and why.

Strength is part of your foundation.

In the ANC House model, durability is the foundation. Race-specific execution sits on it, then Critical Power and Critical Speed, and VO₂ max is the roof. A weak layer caps everything above it. Strength belongs in the foundation. Its job is resilient, efficient movement: lower energy cost at the same pace, handling repeated loading without breaking down, and stronger bones, tendons and connective tissue. Muscle mass is not the goal.

It starts when Base / Durability starts.

After your last race of the season you get a Flex week. Then you move into Base / Durability, and strength starts with it. That is on purpose. Base / Durability is mostly ANC Zone 1 work. Our Zone 1 is the steady aerobic work many people call Zone 2, and it ends at LT1. That leaves room in the week to learn the lifts and recover from them. Here is how we set your zones.

Two sessions a week is the normal prescription.

Our normal prescription is two strength sessions a week, placed on your lighter training days so your key bike and run sessions come first. It is still individual. Your intake, a strength plan you already follow, health decisions, testing and your races can change it, and we adjust around them rather than doubling up.

The same six patterns, every block.

Every program is built on six movement patterns:

Squat
Hinge, the hip-driven posterior chain work
Step-up, lunge or carry
Calf work, for both the gastrocnemius and the soleus
A plyometric element
Trunk stability

Your strength type changes how we progress those patterns. The patterns stay the same. An athlete who tolerates load well builds the weight steadily. An explosive athlete who gets sloppy earns weight with control first. An athlete who adapts fast and plateaus gets new versions each block. If you have an injury history or limited mobility, we add control, slow the tempo and cap the load before we add weight.

The load progresses with the season.

Across a season, strength follows a general progression. You start by learning the movements. Then you build. Then the work gets heavier. Before your main race you move to maintenance, with the smallest dose that holds what you built. That order is the concept, not a fixed calendar every athlete follows in a straight line. The timing is set for each athlete and adjusted to their block, their races and how they are responding. Your strength type shapes how each phase looks. In Base / Durability, an athlete who tolerates load well starts light and adds weight, at 8 to 12 reps. An explosive athlete uses light to moderate weight with slow three to five second lowering. An athlete who adapts fast rotates versions of each lift and keeps the load steady. Plyometrics are low or absent in Base, come in as light skips and pogos in Build, can add jumps and bounds in VO₂ max work, and are only maintained close to the race. Jumps are added only when your mechanics are solid, so not every VO₂ max block brings them.

Conceptual timeline from left to right: a Flex week after the season's last race, then from Base / Durability onward the general strength order learn the movements, build, heavier strength, and maintain with the smallest dose that holds what you built, ending at the main race. Timing and frequency are individual; no phase lengths shown. — From ANC coaching sources. A conceptual example, adjusted for each athlete: normally two sessions a week, changed for intake, an existing strength plan, health, testing and races. No phase lengths are shown because timing is set per athlete.

What strength won't do for you.

The research on lactate-threshold power and speed is mixed, and lactate threshold is not the same measure as Critical Power or Critical Speed. So we don't promise that lifting will raise your Critical Power or Critical Speed. We test those, and your zones come from the tests. What strength gives you is a sturdier foundation under them. In the research, that showed up as better economy in trained runners and cyclists and more power at the end of a long laboratory ride. Strength-based prevention programs also reduced injury risk in some studied populations, though the exact benefit for endurance athletes is less certain.

Two sessions from the ANC 2.0 Strength library, Weeks 13 to 16

Here is what those two weekly sessions look like further into the progression, after the learning weeks: Simple Strength Pick From The Menu, Day 1 and Day 2, Weeks 13 to 16, as written in TrainingPeaks. Earlier weeks look lighter and simpler, and your coach sets where you start.

Simple Strength Pick From The Menu, Day 1, Weeks 13 to 16

SIMPLE STRENGTH – STRONG GAINS · Weeks 13–16: pick from the menu (day 1)

Pick ONE exercise from each category. 2–3 sets of 10–12 reps (or 4–6 reps for heavy strength). Rest 60–90 seconds between sets.

Pick exercises that match your equipment, feel good for YOUR body, and you can perform with excellent form.

PLYOMETRICSPogo Jumps · Jump Rope · Box Jumps · Skipping · Single-Leg Hops

SQUAT / LUNGEBulgarian Split Squat · Reverse Lunge · Forward Lunge · Step-Up · Goblet Squat · Single-Leg Box Squat · Lateral Step-Down

HINGESingle-Leg RDL · Single-Leg Glute Bridge · Single-Leg Hip Thrust · Single-Leg Deadlift (Kickstand) · Romanian Deadlift (RDL) · Kettlebell Swing · Banded Single-Leg RDL

PUSHPush-Up · Single-Arm Dumbbell Chest Press · Dumbbell Bench Press · Single-Arm Overhead Press · Half-Kneeling Press · Landmine Press · Floor Press

PULLPull-Up · Assisted Pull-Up · Single-Arm Dumbbell Row · Inverted Row · Bird Dog Row · Lat Pulldown · Bent-Over Barbell Row

CALF & HIP STABILITYSingle-Leg Calf Raise · Single-Leg Balance · Eccentric Calf Raises · Single-Leg Mini Squats · Banded Clamshells · Banded Lateral Walk · Single-Leg Hip Thrust

CARRYFarmer's Carry · Suitcase Carry · Overhead Carry · Front Rack Carry · Waiter's Carry · Goblet Carry · Asymmetric Carry

SINGLE-LEG: Bulgarian Split Squat · Single-Leg RDL · Step-Up · Reverse Lunge · Forward Lunge · Lateral Step-Down · Single-Leg Glute Bridge

ANTI-CORE: Plank · Side Plank · Pallof Press · Dead Bug · Bird Dog · Hollow Body Hold · Stir the Pot

Keep it simple!

Simple Strength Pick From The Menu, Day 2, Weeks 13 to 16

SIMPLE STRENGTH – STRONG GAINS · Weeks 13–16: pick from the menu (day 2)

Pick ONE exercise from each category — a different one from day 1. 2–3 sets of 10–12 reps (or 4–6 reps for heavy strength). Rest 60–90 seconds between sets.