Dorsiflexion, plantar-flexion, and neutral ankle positions during passive resistance assessments of the posterior hip and thigh muscles

Abstract

Context: Passive straight-legged-raise (SLR) assessments have been performed with the ankle fixed in dorsiflexion (DF), plantar-flexion (PF), or neutral (NTRL) position. However, it is unclear whether ankle position contributes to differences in the passive resistance measured during an SLR assessment.

Objective: To examine the influence of ankle position during an SLR on the passive torque, range of motion (ROM), and hamstrings electromyographic (EMG) responses to passive stretch of the posterior hip and thigh muscles.

Design: Crossover study.

Setting: Research laboratory.

Patients or other participants: A total of 13 healthy volunteers (5 men: age = 24 ± 3 years, height = 178 ± 6 cm, mass = 85 ± 10 kg; 8 women: age = 21 ± 1 years, height = 163 ± 8 cm, mass = 60 ± 6 kg).

Intervention(s): Participants performed 6 randomly ordered passive SLR assessments involving 2 assessments at each condition, which included the ankle positioned in DF, PF, and NTRL. All SLRs were performed using an isokinetic dynamometer programmed in passive mode to move the limb toward the head at 5°/s.

Main outcome measure(s): During each SLR, maximal ROM was determined as the point of discomfort but not pain, as indicated by the participant. Passive torque and EMG amplitude were determined at 4 common joint angles (θ) separated by 5° during the final common 15° of ROM for each participant.

Results: Passive torque was greater for the DF condition than the NTRL (P = .008) and PF (P = .03) conditions at θ3 and greater for the DF than NTRL condition (P = .02) at θ4. Maximal ROM was lower for the DF condition than the NTRL (P = .003) and PF (P < .001) conditions. However, we found no differences among conditions for EMG amplitude (P = .86).

Conclusions: These findings suggest that performing SLRs with the ankle positioned in DF may elicit greater passive torque and lower ROM than SLRs with the ankle positioned in PF or NTRL. The greater passive torque and lower ROM induced by the DF condition possibly were due to increased tension in the neural structures of the proximal thigh.

Keywords: hamstrings muscles; neural tension; passive torque; range of motion; stiffness.

Figure 1.

The instrumented straight-legged–raise assessment technique as seen from the, A, left and, B, right sides of the participant. The isokinetic dynamometer was programmed in passive mode to move the limb toward the head at 5°/s. For each instrumented straight-legged raise, the ankle was immobilized in, C, 10° of dorsiflexion, D, 10° of plantar flexion, or E, a neutral 0° position. The lines in C, D, and E represent the angles at which the ankle was positioned for each condition.

Figure 2.

A, The electromyographic (EMG) signal from the biceps femoris and, B, passive angle-torque curve assessed during a single, passive, instrumented straight-legged raise of the posterior muscles of the hip and thigh. For visualization, the fourth-order polynomial regression and the raw angle-torque curves recorded for this participant with the ankle in neutral, dorsiflexion, and plantar-flexion positions also were plotted. The large rectangular shaded area represents the final 15° of range of motion that was common to all ankle conditions (dorsiflexion, plantar flexion, and neutral). The vertical white boxes represent every fifth degree in the final 15° of range of motion (θ₁, θ₂, θ₃, and θ₄), where passive torque and EMG amplitude values were calculated and used for analysis.

Figure 3.

Maximal passive hip-flexion range-of-motion values of the posterior muscles of the hip and thigh for the dorsiflexion, plantar-flexion, and neutral conditions. Values are means ± standard errors. ^a Indicates differences for range of motion among ankle conditions (dorsiflexion < neutral; dorsiflexion < plantar flexion) (P < .05).

Figure 4.

Passive torque values at each joint angle of the posterior muscles of the hip and thigh for the dorsiflexion, plantar-flexion, and neutral conditions. Values are means ± standard errors. ^a Indicates differences among joint angles (θ₁ < θ₂ < θ₃ < θ₄) for the dorsiflexion, neutral, and plantar-flexion conditions (P < .05). ^b Indicates differences among ankle conditions at θ₃ (dorsiflexion > neutral; dorsiflexion > plantar flexion) and θ₄ (dorsiflexion > neutral) (P < .05).