Physiology
The mineral content per unit volume of bone. Bone density peaks in the early 30s then declines ~0.3-0.5% per year. Loaded carry training applies the mechanical stress that maintains density at the hip and spine.
The 2026 Wake Forest INVEST study clarified an important nuance: standing in a weighted vest doesn't deliver the same benefit as walking in one. Movement is required for the loading-and-unloading cycle that signals bone remodeling.
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Pandolf Equation
The standard biomechanical model for predicting metabolic cost during loaded walking. Inputs: body weight, load, walking speed, terrain factor, and grade. Output: calorie burn per hour.
VO₂ Max
The maximum rate at which the body can use oxygen during exercise. The gold-standard measure of aerobic fitness. Rucking improves VO₂ max comparably to moderate-intensity running with much lower injury rates.
HRV (Heart Rate Variability)
The variation in time between heartbeats. Higher HRV indicates a healthier autonomic nervous system and better recovery capacity. Zone 2 rucking improves HRV without the cortisol cost of high-intensity training.
Posterior Chain
The muscle group on the back side of the body: erector spinae (lower back), glutes, hamstrings, calves. Rucking trains the posterior chain in an integrated way that desk-bound modern life chronically under-uses.
MET (Metabolic Equivalent)
A unit of measure for the energy cost of physical activity. 1 MET ≈ resting energy expenditure. Rucking at moderate pace with a 30 lb load is roughly 6-8 METs, similar to jogging at 5 mph.
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