Effects of 20 Weeks of Endurance and Strength Training on Running Economy, Maximal Aerobic Speed, and Gait Kinematics in Trained Runners

Study Context and Rationale

• Article investigated combined endurance + strength training over 20 weeks in nationally-trained long-distance runners.

• Aimed to see effects on:

  • Running Economy (RE)

  • Maximal Aerobic Speed (MAS)

  • Physiological thresholds (VT1, VT2, VO2max)

  • Gait kinematics & neuromuscular variables (CT, FT, SF, SL, Kleg, vertical oscillation)

• Motivation:

  • Once VO2max plateaus (~70\,\text{mL·kg^{-1}·min^{-1}}) performance is mainly determined by RE.

  • Biomechanics, training composition (interval vs. continuous, strength, footwear) can alter RE.

Key Definitions & Concepts

• VO2max: Highest rate of O2 uptake during exhaustive exercise.

• Running Economy (RE): Steady-state VO2 (or energy) required at a set sub-max speed; expressed as:

  • \text{Oxygen Cost (OC)} = \frac{\text{mL O}_2}{\text{kg·min}}

  • \text{Energy Cost (EC)} = \frac{\text{kJ}}{\text{kg·km}}

• Ventilatory thresholds

  • VT1: First rise in VE/VO2 without rise in VE/VCO2 – aerobic threshold.

  • VT2: Non-linear rise in both VE/VO2 & VE/VCO2 – anaerobic threshold.

• Maximal Aerobic Speed (MAS): Treadmill speed at which VO2max occurs.

• Spatiotemporal variables: Contact time (CT), Flight time (FT), Step frequency (SF), Step length (SL), Leg stiffness (Kleg), Vertical oscillation.

Participant Profile

• n = 18 (13 ♂, 5 ♀)

• Age 25.56 \pm 5.20 y; Height 170.24 \pm 7.93 cm; Mass 58.70 \pm 5.45 kg

• Performance: 33:41 \pm 04:21 (10 km); World Athletics score 831.89 \pm 149.26 points

• Inclusion: ≥3 runs·wk⁻¹, injury-free ≥3 mo, 10 km <35 min (♂) / <40 min (♀).

Experimental Design

• Pre–post design (20-week intervention)

• Control of confounders: identical test time, footwear, nutrition, 24 h no caffeine/alcohol, 48 h no heavy exercise.

• Environment: 529 m altitude; 20–25^{\circ}\text{C}; 35–40\% RH.

Testing Battery

1. Anthropometry: Stadiometer & scale (Seca).

2. Warm-up: 10 min self-paced treadmill, no stretching.

3. Running Economy Test (RET)

   • 2 × 5-min stages @ 3.06\,\text{m·s^{-1}} (♀) / 3.61\,\text{m·s^{-1}} (♂)

   • 1 % slope; 2-min passive recovery.

   • RER confirmed steady state (<1.0, 0.85 \pm 0.04 ).

4. Graded Exercise Test (GXT)

   • Start 2.78\,\text{m·s^{-1}} for 5 min

   • ↑ speed 0.28\,\text{m·s^{-1}} each minute to volitional exhaustion.

5. Measurements

   • Gas analysis: MedGraphics CPX Ultima (calibrated, <0.5\% error).

   • Spatiotemporal/Gait: Stryd foot pod, 1000 Hz sampling.

   • Determination criteria for VO2max (≥ 2 of):

     • VO2 plateau (<1.5\,\text{mL·kg^{-1}·min^{-1}} change)

     • RER > 1.10

     • HR >90\% age-predicted max

     • Subjective exhaustion.

Energy-Cost Equation (Lusk, 1928)

EC = \frac{VO2 \times CE \times 60}{s \times BM} \times K

• VO2 = O2 uptake (L·min^{-1})

• CE = Caloric equivalent (kJ·L^{-1})

• s = treadmill speed (m·min^{-1})

• BM = body mass (kg)

• K = 1000 (m) converts to km.

Training Intervention (20 Weeks)

• Pyramidal Intensity Distribution (TID): ≈80\% Zone 1 (<60\% MAS), 12–14\% Zone 2 (threshold), 6–8\% Zone 3 (≥90\% MAS).

• Endurance modalities

  • Continuous moderate runs (60–90 min)

  • High-intensity intervals: e.g., 3 \times (6 \times 400\,m + 1000\,m), 2\times16\,\text{min} threshold, 15\times400\,m etc.

• Strength sessions (1–2·wk⁻¹)

  • Medium loads 50–70\% 1RM: squats, hip thrust, Bulgarian squat, single-leg deadlift.

  • Core endurance: planks, mountain climbers, dead bugs.

  • Plyometrics: box & drop jumps, strides.

  • Sprints: 8 \times100\,m (max, 1-min rest).

• Average session duration 60–90 min; monitoring via Garmin/Strava.

Statistical Approach

• Data = \text{mean} \pm SD

• Normality: Shapiro–Wilk.

• Pre–post: paired t-tests (SPSS 29).

• Effect size: Cohen d (small ≥0.2, medium ≥0.5, large ≥0.8).

• Significance: p < 0.05.

Results Summary

Running Economy Test

• OC ↑ 4\% (p = 0.011, d = 0.677)\;\Rightarrow worse RE.

• EC ↑ 3.4\% (p = 0.011, d = 0.672).

• Gait variables (CT, FT, SF, SL, Kleg, vertical osc.) – no significant change.

Graded Exercise Test

• Speeds

  • VT1 ↑ 9.4\% (p < 0.001, large ES)

  • VT2 ↑ 3.7\% (p = 0.004)

  • MAS ↑ 2.8\% (p = 0.004)

• Physiology

  • Relative VO2max ↑ 4.6\% (p = 0.011)

  • Absolute VO2max ns (trend ↑ 0.33\,L·min^{-1})

  • %VO2max at VT1 ↑ 4.8\% (p = 0.014); VT2 ns.

  • OC at VT1 ↑ 9.1\%; OC at VT2 ↑ 5.9\%.

• Gait at MAS – no sig. changes in CT, FT, SF, SL, Kleg, vertical osc.

Discussion & Interpretation

• Inverse relationship between VO2max ↑ and RE ↓ replicated (refs 31–32).

• Physiological prioritisation: Training block likely emphasised aerobic power & high-intensity work (cross-country race prep) ⇒ improved VO2max, MAS, thresholds, but compromised efficiency.

• Biomechanics static: Even with plyometrics/strength, no change in CT, Kleg etc. at tested speeds; biomechanical optimisation may need longer exposure or different stimuli.

• Comparisons

  • Prior 8-week endurance-only studies (Rodríguez-Barbero 2023) improved RE without kinematic change.

  • Elite longitudinal data (Arrese 2005) show performance ↑ despite stable VO2max, indicating ceiling effects; current cohort not yet at ceiling.

Practical Applications

• Decide focus:

  • To improve RE ⇒ emphasise moderate-intensity volume, possibly reduce high-intensity load.

  • To improve MAS/VO2max ⇒ pyramidal TID with 6–8\% very-high intensity and structured intervals effective.

• For coaches of team/field sports utilising running: similar mixed-method approach can raise aerobic ceiling without altering mechanics.

• Monitoring cardiometabolic markers (threshold speeds, VO2max) may be more informative than gait metrics during season.

Limitations to Note

• Fixed absolute speed in RET ⇒ relative intensity differed among athletes.

• Gait at MAS analysed over 1-min excerpt; may miss kinematic settling.

• Small female sample; sexes pooled.

• No non-training control group.

Ethical & Methodological Compliance

• Ethics approval: CEIC926 (Nov 2022).

• Participants gave written informed consent; study followed Declaration of Helsinki.

• Open-access publication under CC-BY 4.0.

Connections to Prior Literature & Theories

• Confirms Saunders 2004 & Barnes 2015: strength + high-load plyometrics can aid performance, though not necessarily RE.

• Reinforces concept of economy–capacity trade-off (Noakes 2004, Lucia 2002).

• Supports training-intensity distribution models (Casado 2022) advocating pyramidal distribution for distance runners.

Key Numerical Cheat-Sheet

• Intervention duration: 20\,\text{weeks}

• RET speed: 3.06\,\text{m·s^{-1}} (♀), 3.61\,\text{m·s^{-1}} (♂)

• GXT ramp: +0.28\,\text{m·s^{-1}}·min⁻¹

• VT1 speed change: +1.23\,\text{km·h^{-1}} (≈9.4\%)

• MAS pre/post: 19.44 \rightarrow 20.00\,\text{km·h^{-1}}

• Relative VO2max pre/post: 61.55 \rightarrow 64.53\,\text{mL·kg^{-1}·min^{-1}}

• RE deterioration: \approx 3.5\%

Equations & Conversions Recap

• VO2max criteria listed above.

• \text{Speed (m·s^{-1})} = \frac{\text{km·h^{-1}}}{3.6}

• Leg stiffness estimate (Stryd): K{leg} = \frac{F{peak}}{\Delta L} (device algorithm).

Study Take-Home Message

• A 20-week mixed endurance + strength program with pyramidal intensity distribution increases aerobic power (VO2max, MAS, VT speeds) but slightly worsens running economy; gait mechanics remain unchanged. Coaches must balance high-intensity load with economy-oriented work depending on performance goals.