Leg intramuscular pressures and in vivo knee forces during lower body positive and negative pressure treadmill exercise

Abstract

Quantifying muscle and joint forces over a broad range of weight bearing loads during exercise may provide data required to improve prosthetic materials and better protect against muscle and bone loss. Collectively, leg intramuscular pressure (IMP), ground reaction force (GRF), and the instrumented tibial tray force measurements provide a comprehensive assessment of leg muscle and joint biomechanical effects of gravity during exercise. Titration of body weight (BW) by lower body negative pressure (LBNP) and lower body positive pressure (LBPP) can reproducibly modulate IMP within leg muscle compartments. In addition, previous studies document peak tibial forces during various daily activities of 2.2 to 2.5 BW. The study objective was to determine the IMPs of the leg, axial compressive force on the tibia in vivo, vertical GRF, and knee range of motion during altered BW levels using LBPP and LBNP treadmill exercise. We hypothesize that peak GRF, peak tibial forces, and peak IMPs of the leg correlate linearly with percent BW, as generated across a broad range of upright LBPP and supine LBNP exercise. When running at 2.24 m/s the leg IMPs significantly increased over the loading range of 60% to 140% BW with LBPP and LBNP (P < 0.001); as expected, leg IMPs were significantly higher when running compared with standing (P < 0.001). During upright LBPP, total axial force at the knee increased linearly as a function of BW at 0.67 m/s (R(2) = 0.90) and 1.34 m/s (R(2) = 0.98). During supine LBNP, total axial force at the knee increased linearly as a function of BW at 0.67 m/s (R(2) = 0.98) and 1.34 m/s (R(2) = 0.91). The present study is the first to measure IMPs and peak tibial forces in vivo during upright LBPP, upright LBNP, and supine LBNP exercise. These data will aid the development of rehabilitation exercise hardware and prescriptions for patients and astronauts.

Physiological Responses During the Lower Body Positive Pressure Supported Treadmill Test

“…LBPPS also raises the intramuscular pressure, which activates the muscle mechanoreflex, resulting in increased BP [17]. Furthermore, positive pressure on the lower extremities limits the blood supply to the active muscles, and hence metabolites accumulate and a pressure metaboreflex is triggered [1819]. …”

Muscle Activation and Estimated Relative Joint Force During Running with Weight Support on a Lower-Body Positive-Pressure Treadmill

“…Patil et al 3 found that the peak tibial force at 25% BW relative to peak tibial force at 100% BW was 1.9 BW/5.1 BW, corresponding to 37% at 25% BW. Macias et al 19 found an uneven load distribution between the instrumented leg and the healthy leg at high relative BWs and "high" velocity, tending toward more load on the healthy leg. This means that, in healthy subjects, with an even load distribution between left and right leg, we may expect values lower than 37%, as found by Patil et al 3 Macias et al 19 found values of approximately 30% at 20% BW (based on readings from their Figure 6).…”

“…Macias et al 19 found an uneven load distribution between the instrumented leg and the healthy leg at high relative BWs and "high" velocity, tending toward more load on the healthy leg. This means that, in healthy subjects, with an even load distribution between left and right leg, we may expect values lower than 37%, as found by Patil et al 3 Macias et al 19 found values of approximately 30% at 20% BW (based on readings from their Figure 6). Again, this value could be a bit overestimated due to the uneven weight distribution between the implanted knee and the healthy knee.…”

“…Again, this value could be a bit overestimated due to the uneven weight distribution between the implanted knee and the healthy knee. 19 For comparison, we estimated knee joint force at 20% BW to be 24% (2.22 m/s) and 29% (3.3 m/s) of the initial value at 100% BW for healthy subjects. Thus, our results regarding estimated joint forces mainly agree with previous results obtained with direct measurements of joint force in instrumented knee prostheses.…”

Intermuscular pressure between synergistic muscles correlates with muscle force

“…It has been known since the first attempts to characterise the mechanical properties of skeletal muscles (Hill, 1948) that they generate significant IaMP during active contraction. Furthermore, IaMP was reported to correlate linearly with contraction force in skeletal muscles of humans, cats and rabbits (Baskin and Paolini, 1967;Sadamoto et al, 1983;Parker et al, 1984;Petrofsky and Hendershot, 1984;Sejersted et al, 1984;Aratow et al, 1993;Nakhostine et al, 1993;Davis et al, 2003;Ward et al, 2007;Winters et al, 2009;Macias et al, 2012). According to present knowledge, muscle contraction causes a reversible distortion of muscle architecture accompanied by an increase of IaMP, owing to muscle incompressibility (Swammerdam, 1737;Hill, 1948;Jenkyn et al, 2002).…”