VO2 Max and Strength: How to Train Both

The Interference Phenomenon in Concurrent Training

Simultaneously training for cardiorespiratory fitness and musculoskeletal adaptation—known as concurrent training—presents well-documented physiological trade-offs. Pioneering work by Hickson demonstrated that while ten weeks of concurrent high-intensity endurance and resistance training improved maximal oxygen uptake ($\dot{V}{\text{O}}_2\text{max}$) to the same degree as endurance training alone (~17% on treadmill, ~20% on cycle ergometer), lower-body strength gains plateaued at weeks 7–8 and subsequently declined during weeks 9–10 [6]. Subsequent investigations confirmed that high-intensity concurrent training blunts muscle fiber hypertrophy (attenuating increases to ~16% compared to ~28% with resistance training alone) [6]. A meta-analysis quantified this interaction, showing that resistance training alone yielded effect sizes of 1.71 for strength and 1.22 for hypertrophy, whereas concurrent training attenuated these effects to 1.28 and 0.80, respectively [6].

Preserving strength, power, and muscle cross-sectional area (MCSA) while driving improvements in $\dot{V}{\text{O}}_2\text{max}$ requires strategic selection of endurance modalities, precise intra-day session spacing, and conservative weekly volume management.

Endurance Modality Selection and Biomechanical Stress

The choice of endurance modality substantially alters both neuromuscular fatigue and hypertrophic outcomes. Network meta-analytic data across 40 studies (841 participants) show that while all concurrent training modalities reduce maximal lower-body strength gains relative to resistance training alone, high-intensity interval training (HIIT) mitigates strength interference most effectively (SMD = -0.08, 95% CI: -0.25 to 0.08) [3]. Furthermore, HIIT was the only concurrent endurance modality found to be superior to resistance training alone for explosive strength development (SMD = 0.06, 95% CI: -0.21 to 0.33) [3].

Regarding muscle mass, concurrent high-intensity interval running with resistance training (SMD = 0.15, 95% CI: -0.46 to 0.76) and moderate-intensity continuous cycling with resistance training (SMD = 0.07, 95% CI: -0.24 to 0.38) both favored increases in MCSA compared to resistance training alone [3].

Biomechanical mechanics also govern systemic and localized recovery. Running produces ground reaction forces 3 to 5 times body weight with pronounced eccentric braking, which induces structural muscle damage and elevates plasma creatine kinase [14]. Conversely, concentric-dominant modalities such as cycle or rowing ergometry eliminate these eccentric impacts, minimizing exercise-induced muscle damage and subsequent interference with hypertrophic pathways [14]. In trained rugby players performing morning sprint intervals prior to afternoon resistance training with a 4-hour recovery window, running sprints induced significantly higher ratings of perceived exertion (7.7 ± 1.1) and lower subjective wellbeing (17.9 ± 4.1) over subsequent days compared to cycling sprints (7.4 ± 1.1 RPE; 20.1 ± 3.9 wellbeing) or control conditions (6.7 ± 1.5 RPE; 21.1 ± 3.6 wellbeing) [13].

Exercise Sequencing and Session Spacing Intervals

Intra-Session Sequence

Evidence demonstrates that intra-session exercise sequence does not compromise aerobic adaptations. A systematic review and meta-analysis of 19 randomized controlled trials (482 participants) revealed no significant difference between strength-before-endurance (S-E) and endurance-before-strength (E-S) exercise order on $\dot{V}{\text{O}}_2\text{max}$ gains (SMD = 0.02, 95% CI: -0.21 to 0.25, p = 0.859) [1]. Similarly, a 13-week trial in middle-aged adults demonstrated that exercise sequence had no significant impact on $\dot{V}{\text{O}}_2\text{max}$, forced vital capacity (FVC), or forced expiratory volume in 1 second (FEV1) [10].

However, exercise order significantly influences strength and power. The S-E sequence produces significantly greater lower-limb strength adaptations compared to E-S (SMD = 0.19, 95% CI: 0.02 to 0.37, p = 0.032), with distinct advantages observed for knee extension (p = 0.026), knee flexion (p = 0.040), female cohorts (p = 0.017), older adults (p = 0.039), programs lasting over 8 weeks (p = 0.002), and frequencies of twice weekly (p = 0.003) [1]. While overall long-term hypertrophy and maximal strength may remain viable across different sequencing structures [4], [11], executing resistance training prior to endurance bouts mitigates residual fatigue and optimizes neuromuscular adaptations, explosive power, and countermovement jump performance [4], [11].

Inter-Session Spacing and Molecular Signaling

At the cellular level, acute endurance exercise activates adenosine monophosphate-activated protein kinase (AMPK), which suppresses the mechanistic target of rapamycin complex 1 (mTORC1) pathway—a primary driver of muscle protein synthesis (MPS) [14]. AMPK inhibits mTORC1 through two distinct mechanisms: phosphorylating tuberous sclerosis complex 2 (TSC2), which converts Rheb into its inactive GDP-bound form, and directly phosphorylating the Raptor subunit of mTORC1 to trigger inhibitory binding [14]. Performing high-intensity endurance bouts immediately adjacent to resistance training blunts the phosphorylation of downstream p70S6K for up to 8 hours [14].

To decouple these competing intracellular signals:

• When an endurance-first sequence is mandatory, a minimum recovery interval exceeding 3 hours is recommended to mitigate acute molecular interference [4].
• When assessing neuromuscular performance, competitive athletes separated from morning sprint interval exercise by a 4-hour rest window maintained afternoon bar velocity in the bench press and box squat, as well as countermovement jump height [13].
• To prevent AMPK from overriding mTORC1-mediated protein translation, separating sessions by at least 6 hours—and ideally 8 to 24 hours—provides superior isolation [14]. Acute AMPK activity returns to baseline within 180 minutes post-exercise when adequate carbohydrates are provided, whereas mTORC1 signaling and MPS remain elevated for 24 to 48 hours following high-tension resistance training [14].
• Carbohydrate availability directly influences this cascade: exercising with low intramuscular glycogen doubles baseline AMPK activation [14]. Ingesting 30–60 g/h of carbohydrates during endurance sessions exceeding 45 minutes, paired with 1.0–1.2 g/kg of fast-digesting carbohydrates and 0.3–0.4 g/kg of protein post-cardio, accelerates glycogen resynthesis and dampens prolonged AMPK signaling [14].

Weekly Volume and Frequency Thresholds

Endurance Dose Limits

Endurance volume and frequency exhibit a negative correlation with maximal strength development [7]. Endurance sessions executed 3 times per week frequently impair muscular strength and fitness development, whereas 1 to 2 sessions per week exhibit a markedly smaller detrimental impact [7]. Furthermore, longer daily durations (50–60 minutes versus 20–30 minutes) and higher weekly frequencies (3 to 5 sessions per week) compound the interference effect on strength progression [7].

Resistance Training Dose-Response

To preserve strength and hypertrophy, resistance training volume must be quantified accurately. Multi-level meta-regressions by Pelland et al. (evaluating 67 studies and 2,058 participants) established that a 'fractional' set quantification model (weighting direct sets at 1.0 and indirect compound sets at 0.5) provides the most robust empirical framework for predicting strength and hypertrophic adaptations [17], [18].

This meta-regression established a 100% posterior probability that the marginal slope exceeds zero for weekly set volume on both hypertrophy and strength, confirming that higher volumes drive adaptations [17]. However, both outcomes follow a dose-response model characterized by diminishing returns, with diminishing returns being considerably more pronounced for strength gains than for muscle hypertrophy [17]. Higher weekly training frequencies also exhibited a 100% posterior probability of increasing strength gains (with diminishing returns), whereas the effect of frequency on hypertrophy was compatible with negligible changes when volume is equated [17]. Prior dose-response work corroborates that weekly volumes exceeding 5 sets yield superior strength gains over ≤5 sets (SMD: 0.18, p = 0.003) [19], with ≥9 sets per muscle group yielding larger hypertrophic responses (ES = 0.46) [19].

When managing training intensity, muscle hypertrophy occurs across a wide loading spectrum (≤8 RM, 9–15 RM, and >15 RM) when sets are performed to volitional failure (p = 0.113–0.469) [21]. However, maximal strength adaptations are significantly superior when utilizing high-load (SMD = 0.60–0.63, p < 0.003) and moderate-load (SMD = 0.34–0.35) training relative to low-load protocols [21].

Athlete Training Status and Sex Differences

Individual characteristics alter the magnitude of the concurrent interference effect:

• Training Status: Untrained individuals experience minimal interference, developing strength, hypertrophy, and $\dot{V}{\text{O}}_2\text{max}$ concurrently with responses comparable to single-mode training [7], [9], [21]. Conversely, trained endurance athletes experience blunted $\dot{V}{\text{O}}_2\text{max}$ improvements when adding resistance exercise compared to untrained individuals (p = 0.04) [9]. Well-trained resistance athletes display attenuated anabolic gene and protein expression alongside reduced neuromuscular adaptations when endurance volume is introduced [7]. Advanced athletes operate near training saturation ceilings, where requirements for high neural drive, motor unit synchronization, and minimal antagonist co-contraction elevate fatigue and injury susceptibility during concurrent workloads [22]. Highly trained individuals require a greater number of specific sessions to elicit incremental strength adaptations [21].
• Sex Differences: Meta-analytic findings indicate that concurrent training blunts lower-body maximal strength in males (SMD = -0.43, 95% CI: -0.64 to -0.22) but not in females (SMD = 0.08, 95% CI: -0.34 to 0.49; between-group difference p = 0.03) [9]. Additionally, females demonstrate pronounced strength benefits when prioritizing the strength-first intra-session sequence (p = 0.017) [1].