THIGH-CALF AND HEEL-GLUTEUS CONTACT FORCES IN HIGH FLEXION 

(EXPERIMENTAL RESULTS) 

Jonisha P. Pollard
 

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA
 

email: JPollard@cdc.gov, web: http://www.cdc.gov/niosh/mining
 

INTRODUCTION 

In restricted vertical working heights such as lowseam coal mines, workers are forced to assume 

kneeling or squatting postures to perform work. 

These postures are associated with increased risks 

for the development of significant knee pathologies 

such as meniscal tears and osteoarthritis [1,2]. 

Previous research has shown an increased applied 

knee flexion moment when kneeling in high flexion 

[3]. However, these models have been applied to 

flexion up to 140° which neglects contact between 

the thigh and calf which occurs beyond 140°. In 

addition to thigh-calf contact, when kneeling near 

full flexion there may be additional contact between 

the heel and gluteal muscles. 

To the author’s knowledge, heel-gluteus contact has 

not been previously investigated, but thigh-calf 

contact has received some attention. Zelle (2007) 

reported thigh-calf contact forces up to 30% 

bodyweight (BW) [4]. Zelle (2009) reported 

decreased knee forces when accounting for thighcalf contact [5]. Caruntu (2003) reported erroneous 

force and moment estimations when thigh-calf 

contact was neglected from models to determine 

muscle and ligament forces [6]. 

In this study thigh-calf and heel-gluteus contact 

forces were quantified to determine their effect on 

the externally applied flexion moment in high 

flexion. 

METHODS 

Ten subjects were recruited (7 male; age: 34 ± 17 

years; weight: 683 ± 98 N; height 169 ± 8 cm) from 

the National Institute for Occupational Safety and 

Health in Pittsburgh, PA. No subjects had a history 

of knee pathologies. 

Subjects were instructed to stand while a clinical 

® seating pressure assessment system (ClinSeat , 

Tekscan Inc., South Boston, Massachusetts, USA) 

was placed along their lower right leg from the 

popliteal to the heel. They were then instructed to 

squat and pressure data was collected for 5 seconds. 

(Figure 1) Next, the subject kneeled on the floor at 

90° flexion. The pressure sensor was again laid 

across their lower right leg. They then went into full 

flexion while data were collected for 5 seconds. 

During data collection, the distance from the top of 

the sensor to the lateral epicondyle of the femur was 

measured and recorded. Subjects were given no 

specific instructions on kneeling, and therefore 

assumed postures which they felt caused the least 

discomfort. 

The supplied software (Advanced ClinSeat, 

Tekscan Inc., South Boston, Massachusetts, USA) 

was used to record the pressure distributions and 

calculate the centers of pressure and total forces at 

the thigh-calf and heel-gluteus contact areas. 

Figure 1: Experimental data collection 

RESULTS AND DISCUSSION 

In all subjects, thigh-calf contact forces when 

squatting were at least 20% BW, with a mean of 39 

± 14% BW (Figure 2). Thigh-calf contact in full 

flexion was less than squatting with a mean of 28 ± 

13% BW (Figure 3). The centers of pressure were 
6.6 and 6.1 inches inferior of the epicondylar axis 

for squatting and kneeling near full flexion, 

respectively. In 7 of the 10 subjects, kneeling near 

full flexion resulted in heel-gluteus contact. These 

contact forces were less than the thigh-calf contact 

forces, with a mean of 11 ± 6% BW and a center of 

pressure 16.3 inches inferior of the epicondylar 

axis; approximately at the subject’s heel. 

Figure 2: Typical pressure distribution (psi) for 

squatting. 

 

 

Figure 3: Typical pressure distribution (psi) for 

kneeling near full flexion.3 

Thigh-calf and heel-gluteus contact forces created 

extension moments about the knee. Mean thigh-calf 

contact moments when squatting and kneeling near 

full flexion were 4% BW*Ht and 3% BW*Ht, 

respectively. The mean heel-gluteus contact 

moment was 3% BW*Ht. 

The forces and moments generated by thigh-calf 

contact have been shown to greatly affect the 

muscle and ligament forces as well as the stresses in 

knee structures. Caruntu and colleagues (2003) 

found that when accounting for thigh-calf contact, 

quadriceps forces decreased by 700 N and medial 

collateral ligament forces increased by 50% [6]. 

Zelle (2009) found reductions in compressive knee 

forces by 1.99 times BW when thigh-calf contact 

was included. Contact stresses on the tibial post of 

polyethylene knee replacements also decreased by 

21.2 MPa when including thigh-calf contact [5]. 

Having a comparable moment contribution to thighcalf contact, it is expected that heel-gluteus contact 

will have similar affects on the forces and stresses 

in the internal knee structures. 

CONCLUSIONS 

Thigh-calf and heel-gluteus contact forces act in the 

anterior direction of the shank, thereby extending 

the knee and reducing the applied flexion moment. 

These forces act to stabilize the knee in high flexion 

and may significantly affect calculations in 

computational knee models. 

Traditionally, segment contact forces have been 

neglected from biomechanical models. The 

complexity of modeling tissue deformation and 

pressure distributions may discourage researchers 

from considering these inputs. However, the 

magnitude of these forces were shown to be quite 

large, >30% BW and the moments produced by 

these contact forces may decrease externally applied 

flexion moments by as much as 9% BW*Ht. 

In the future, biomechanical models should account 

for the thigh-calf and heel-gluteus contact as 

neglecting these forces may result in erroneous 

force and moment estimations. 

REFERENCES 

1.	 Anderson JJ, Felson DT. Am J Epidemiol 128, 

179-189, 1988. 

2.	 Sharrard WJW, Lidell FDK. Brit J Industr Med 

19, 195-202, 1962. 

3.	 Nagura T, et al. J Orthop Res 20, 881-886, 2002 

4.	 Zelle J, et al. Clin Biom 22, 821-826, 2007. 

5.	 Zelle J, et al. J Biomech, 2009. 

6.	 Caruntu DI, et al. Summer Bioengineering 

Conference, Key Biscayne, Florida, 2003. 

DISCLAIMER 

The findings and conclusions in this paper are those 

of the author and do not necessarily represent the 

views of the National Institute for Occupational 

Safety and Health.