From Head to Toe: Quantifying Force on the Body While Head-Loading
Course or Client
Measurement and Instrumentation
Advisers: Prof. Thomas Peacock and Dr. Barbara Hughey
Status
Started September 2025
Completed December 2025
Contributions
DOE and Testing
Data Analysis
Presentation and Poster Creation
Final Report
Final Poster
Abstract:
Roughly 17 million women and children in Sub-Saharan Africa are responsible for traveling over 30 minutes to collect clean drinking water for them and their families, making understanding the biomechanics and potential health impacts of head-loading vital. Forces on the foot and head while head-loading a 20L jerry can filled with water at speed and incline conditions of 2.4 to 3.9 km/h and 0 to 10 degrees were measured utilizing force pads attached to the heel of the foot, ball of the foot, and underside of the jerry can. An increase in speed also increased loading on the heel of the foot. A net increase in loading on the ball of the foot was observed with an increase in incline from 0 to 10 degrees, but net decreases in loading on the top of the head and heel of the foot. A shift in primary loading from the heel to the ball of the foot can be expected at about 8.5 degrees.
Background:
The Necessity of Water Hauling and Its Impacts on the Body
Water scarcity is defined as the condition of inadequate supply of water compared to its demand and can be broken up into two primary categories, physical and economic scarcity. In SSA, the prevalence of water scarcity is due mostly to economic constraint, although climate change, population growth, environmental overexploitation is increasing the rate of physical scarcity, which has led to an estimated two-thirds of the population leaving their homes to collect water. Despite so many people (predominantly women and children) having water collection as an everyday part of life SSA, in-depth analyses into the energy expenditure and biomechanics of gendered domestic tasks are limited and difficult. Although head-loading allows for increased balance over uneven terrain, the prevalence of serious health conditions increases, including arthritis (notably osteoarthritis), tumoral calcinosis (calcification of soft tissue around the joints), degenerative disc disease (degradation of the cartilage in the vertebrae), spondylolisthesis (misalignment of the vertebrae), neurological deficits, numbness and loss of feeling in the arms, flattening of the lordotic (spinal) curve, neck stiffness and pain, metatarsal stress fractures, miscarriages, premature births and low birth weight, reproductive organ prolapses, and reduced fertility. Given the necessity of head-loading for so many people (with no end in the foreseeable future), it is critical to understand how force from head-loading may be distributed onto or absorbed by various parts of the body, especially the head and feet.
The Biomechanics of Walking (an Explanation of the Gait Cycle)
Figure 1 depicts the gait cycle (a person’s walking pattern) which can be broken up into two main parts, the stance phase (some or all of the foot is in contact with the ground and weight is supported) and the swing phase (none of the foot is in contact with the ground and body weight is on the ground contacting foot).
Figure 1: A breakdown of the human gait cycle. Physiopedia.
Within the stance phase are the heel strike (heel contacts ground), loading response (ball of foot contacts ground), midstance (body weight transfer), terminal stance (heel off of ground), and pre-swing (heel off the ground) phases [11]. During the stance phase, load on the foot shifts from the heel to the toe. After preparing to leave the ground and transferring load, the foot enters the swing phase which is divided into three parts: initial swing, mid-swing, late swing . Another way to describe the actions of the feet during the gait cycle is through double and single support periods. Single support periods encompass a majority of a person’s walking time where only one foot is in contact with the ground and supports all of the applied load. In double support periods, both feet are in contact with the ground, however most of the time during double support periods the load will not be evenly distributed as weight shifts with the swinging motion of the legs. Similarly, when a foot is in contact within the ground, loading over a single foot will vary with position in the gait cycle. While in the toe-off portion of the gait cycle, loading is concentrated on the ball of the foot and toes versus the heel-strike phase in which loading is concentrated on the heel of the foot. It is important to note that gait cycle patterns differ greatly by age, sex, and individual physical characteristics. In general, females have greater loading on the lateral column of the foot (the side of the foot closest to the fifth or pinky toe) when compared to males. However, males have a greater force-time integral (impulse) over the entire foot. It is also important to note that changes in head position or loading may occur during the gait cycle due to an individual’s stance or disability.
Results:
To analyze broader biomechanical trends, the maximum force value for each occurrence of the gait cycle for each sensor over the 30 second trial interval was found and then averaged. Because of the low variance in force on the top of the head, the entire data set was averaged for this sensor. This averaging process was repeated for the three trials for each test. Using this method, 12 unique datasets were created, one for each speed-angle condition tested. Each data set included the average and its uncertainty for each sensor (top of the head, heel of the foot, and ball of the foot) at the specified speed and incline. This data was then plotted and fitted with either a linear or piecewise model. Figure 2 shows three graphs plotting the maximum force values for each of the three sensors at constant incline over varying speeds. Analyzing these graphs shows that no statistical difference in force on the head occurs as a result of incline or speed. Despite the average experimental value for force on the top of the head being significantly lower than the simplified model’s expected value (measured at 113.09 ± 67 Newtons), measured maximum loading on the foot was consistent with the expected values for all slopes tested, validating the created model. Interestingly, while loading on the heel of the foot increases with speed at constant incline, loading on the ball of the foot does not. A possible explanation for this is that as speed increases, loading over the entire foot does increase, but a bulk of the force is absorbed by the first point of contact. This would explain, then, the upwards trend in loading on the heel even after the switch of primary loading from the heel to the ball of the foot seen in the 10 degree incline graph.
Figure 2: A comparison of average maximum force on the top of the head, heel of the foot, and ball of the foot by incline while head-loading at varying walking speeds.
Figure 3 shows the averaged data at constant speed over varying inclines. By reformatting the data and fitting a piecewise model to the points, a relationship between angle and loading over the foot can be constructed. Around the 8.5 degree incline mark, primary loading on the foot switches from the heel to the ball of the foot, represented by the intersection of the two functions. There are several possibilities for how such a radical shift in loading occurred with the first explanation being similar to that of the minimum loading of the heel during the 0 and 4 degree tests. Calibration or placement on the foot of the force pads before the 10 degree incline test could have been different enough to skew the results and cause this perceived shift in loading. It is known from prior experience that crossing of the force pad wires or improper contact between the foot and inside of the shoe can dramatically alter results. A non-erroneous explanation, however, includes a change in posture that occurs between 4 and 10 degrees that is the body’s way of adjusting to the incline. Background research indicates that to walk up an incline, a person often shifts their center of gravity forwards to resist the downhill force and avoid falling backwards. When head-loading, it is not uncommon for long term exposure to result in flattening of the lordotic curve, a change in spinal anatomy that protrudes the stomach outward. This anatomical change pushes the center of mass more forward and (in theory) makes it easier to climb uphill without leaning forward as much, further supporting the posture change theory.
Figure 3: A comparison of the average maximum forces on the top of the head, heel of the foot, and ball of the foot at constant speed and varying incline.
Conclusions:
Results indicate a significant dependence of loading on the heel of the foot on speed for low angles (0, 4, and 10 degrees) at moderate walking pace (2.4 to 3.9 km/h) during head-loading of a roughly 20 kilogram object. Force changes at these conditions on the top of the head are negligible with respect to both incline and speed. Similarly, loading on the ball of the foot appears to be independent of speed and become the primary source of loading on the foot around the 8.5 degree mark, but further testing is needed to confirm if this is due to error or biomechanical changes. Posture, anatomy, sex, and disability may impact results of loading on the foot should be considered when devising a model to calculate the biomechanics of head-loading on the body, but treatment of the body-object-slope system as a static model for an instantaneous moment in time seems to generally hold up under empirical testing.