By Kelson Geber, MTI Coach/Researcher
Background
In mission-focused training, how you carry weight directly impacts your performance, especially in job-specific scenarios with high physical demands. Whether you’re a soldier, a first responder, or a mountain guide, choosing between a rucksack or a weighted vest can significantly influence your endurance, strength, and overall efficiency. Because our training is centered on mission-direct fitness, understanding these differences is essential for tailoring programs that prepare our athletes for the exact challenges they will face in the field. This article explores the differences between these two load-carrying methods, examining how each impacts your body’s energy expenditure and overall physiological demands. Additionally, we delve into how various terrains and inclines alter your metabolic costs, highlighting the critical role of training in environments that closely mirror real-world conditions.
Metabolic Energy Cost: A Fundamental Consideration
Metabolic energy cost refers to the amount of energy required to perform a particular physical activity. It is a critical factor in physical training, as it influences the endurance, strength, and overall performance of individuals, particularly in demanding environments such as military operations and law enforcement operations, and mountain guiding.
One of the pioneering studies in this field, conducted by Givoni and Goldman (1971), provided a method for predicting metabolic energy costs during walking by accounting for an individual’s body mass, external loads, terrain features, walking speed, and slope. This foundational work laid the groundwork for subsequent research aimed at refining and expanding these predictions to various conditions and activities.
Load Carriage and Energy Expenditure
Load carriage is a critical element of mission-direct fitness training, particularly in military and tactical settings where individuals are required to transport equipment over varying distances and terrains. The energy cost associated with load carriage is substantial and varies depending on whether the load is carried in a rucksack (backpack) or a weighted vest. Understanding these differences is important for optimizing training and ensuring mission readiness.
Metabolic Requirements for Ruck (Backpack) Load Carriage
Carrying a load in a rucksack significantly increases metabolic demands. Several key factors contribute to this heightened energy expenditure:
- Biomechanical Adjustments: When a load is carried on the back, the body’s center of gravity shifts posteriorly. To maintain balance, the torso leans forward, altering the natural gait pattern and increasing the workload on the lower back and legs. This forward lean necessitates greater muscular effort to stabilize the body, particularly during prolonged activities or when moving over uneven terrain.
- Increased Muscle Activation: The load’s posterior placement requires greater activation of the back, core, and leg muscles to prevent tipping and maintain an upright posture. This increased muscle activation leads to higher oxygen consumption and, consequently, greater metabolic costs.
- Oxygen Consumption and Heat Production: The need for additional stabilizing forces during ruck carriage increases the body’s oxygen consumption. Additionally, the rucksack’s weight contributes to higher heat production, which can exacerbate fatigue and increase metabolic demands as the body works to dissipate excess heat.
- Load Distribution: The rucksack’s position away from the body’s center of mass makes it less efficient than other forms of load carriage, such as a weighted vest. The further the load is from the center of mass, the greater the energy required to maintain balance and posture.
While rucksacks present significant metabolic challenges, weighted vests offer different approaches with distinct differences.
Metabolic Requirements for Weighted Vest Load Carriage
Carrying a load in a weighted vest distributes the weight more evenly across the torso, closer to the body’s center of mass. This even distribution helps lower the energy your body needs to move:
- Biomechanical Efficiency: Unlike rucksack load carriage, the load in a weighted vest is positioned closer to the center of mass, reducing the need for significant biomechanical adjustments. The more balanced weight distribution minimizes the torso’s forward lean, which preserves a more natural gait and reduces the strain on the lower back.
- Lower Muscle Activation: Since the load is carried close to the body’s core, the demand for stabilizing muscles is reduced. This results in lower overall muscle activation than rucksack carriage, leading to lower metabolic costs.
- Improved Oxygen Consumption: A vest’s more efficient weight distribution results in less energy expenditure during activities such as walking or running. This efficiency translates to lower oxygen consumption rates, allowing for sustained activity over more extended periods without reaching fatigue as quickly.
- Reduced Heat Production: The load distribution around the torso also helps manage heat better than a rucksack. The body can more effectively dissipate heat with less posterior load concentration, reducing the overall metabolic burden during extended activities.
The Impact of Gradient and Terrain on Energy Expenditure
Walking on inclines and varied terrains presents unique challenges to the body, increasing energy expenditure compared to walking on flat, even surfaces.
The gradient or incline of the terrain is a primary factor that impacts energy expenditure during walking. For example, Bobbert’s (1960) study found that walking on a 10% incline can require 50-70% more energy than walking on flat ground. This increase occurs because the body must work harder to lift against gravity, which engages the quadriceps, calves, and other stabilizing muscles more intensely. As a result, the cardiovascular system also has to work harder to supply the necessary oxygen to these muscles, leading to a higher heart rate and greater overall metabolic demand.
Example: Consider a hiker ascending a steep hill while carrying a backpack. The incline forces the hiker to lean forward slightly to maintain balance, increasing the load on the lower body muscles and requiring more effort to maintain a steady pace.
Beyond the incline, the terrain type also plays a significant role in determining energy expenditure. Richmond et al. (2015) reviewed various terrain factors, revealing how uneven surfaces like loose gravel, rocky paths, or muddy trails increase the energy cost of walking. These types of terrain require continuous adjustments in balance and foot placement, engaging the stabilizing muscles more frequently and increasing the overall effort needed to move forward.
Example: Imagine a soldier carrying a load while navigating a rocky, uneven field. Each step requires careful placement to avoid slipping or tripping, which slows progress and demands more energy from the leg and core muscles to maintain stability.
Takeaways and Considerations
Much of the information discussed here revolves around the metabolic demands of different weight-carrying methods. Dispersing weight evenly and keeping it close to your center of mass is generally more advantageous. However, this is not always practical in scenarios like soldiering, where you need to get low to the ground or crawl, or mountaineering, where bringing your center of gravity close to the rock is crucial, and front-loaded gear would inhibit movement.
Wearing a vest is ideal in limited applications. One example is trail running, where staying upright is essential, and carrying a heavy weight or becoming prone is unnecessary. Other activities like snowmobiling (for avalanche safety) and mountain biking (for hydration) also use vest-like options, but these typically don’t involve carrying significant weight.
Weighted vests are excellent training tools, particularly for developing specific strength attributes, such as in climbing, where upper body and core strength are critical. Additionally, a weighted vest can be beneficial during technical training by adding resistance without disrupting your natural movement patterns.
The research lacks an analysis of wearing both a vest and a ruck together. It’s common to carry body armor with magazines, radios, and other gear on the vest and a ruck on top. Given this reality, it’s important to investigate whether there’s a difference in energy expenditure and performance between this combined load and carrying just the ruck alone.
Our programming primarily uses rucks because that’s what our athletes will wear in real mountain and tactical scenarios. Research shows clear differences between rucks and vests, reinforcing why we train with rucks—to prepare for the real thing.
Sources
Givoni B, Goldman RF. Predicting metabolic energy cost. J Appl Physiol. 1971;30(3):429–33.
Pandolf KB, Givoni B, Goldman RF. Predicting energy expenditure with loads while standing or walking very slowly. J Appl Physiol. 1977;43(4):577–81.
Goldman RF, Iampietro PF. Energy cost of load carriage. J Appl Physiol. 1962;17(4):675–6.
Bobbert A. Energy expenditure in level and grade walking. J Appl Physiol. 1960;15(6):1015–21.
Richmond PW, Potter AW, Santee WR. Terrain factors for predicting walking and load carriage energy costs: review and refinement. J Sport Hum Perf. 2015;3(3):1–26.
Looney DP et al. Metabolic Costs of Walking with Weighted Vests. Med. Sci. Sports Exerc., Vol. 56, No. 6, pp. 1177-1185, 2024 (metabolic_costs_of_walk…).