Mechanical and metabolic profile of locomotion in adults with childhood-onset GH deficiency

Abstract

Objective: The aim of the present study was to evaluate the energy cost and the mechanical work of locomotion in a group of adults with childhood-onset GH deficiency (GHD). Subjects: Eight males with childhood-onset GHD (mean age Ϯ S.D.: 31.7 Ϯ 3.6 years; mean height: 145.1 Ϯ 6.7 cm) and six age-, sex-and exercise-matched normal subjects were studied. Design: GHD patients and healthy controls were requested to walk and run in the speed range of 2-11 km h ¹1. For each condition, simultaneous mechanical and metabolic measurements were taken. Methods: Oxygen consumption, and mechanical internal and external work of locomotion were evaluated with standard open-circuit respirometry and three-dimensional motion analysis respectively. Results: External work was not significantly different between GHD patients and healthy controls, while internal work was higher for patients at all speeds. In walking, the relationships between both the mechanical energy recovery and the metabolic cost with speed were shifted towards lower speeds in patients. As a consequence, the optimal speed of walking, i.e. the speed at which the cost of locomotion is minimum, was lower for GHD patients. Stride frequency was significantly higher (11.2-11.3%) for GHD patients at all speeds of walking and running. GHD patients were unable to run at speeds higher than 8 km h ¹1 for the time needed to reach a metabolic steady state. Conclusion: It appears that both the mechanics and energetics of locomotion in short-statured adults with childhood-onset GHD are not strikingly different from those of healthy controls, thus demonstrating a substantial 'normality' in this group of GHD patients at metabolically attainable speeds. The 'harmonic' body structure and the adherence to allometric transformations in these patients do not exclude the possibility of a different metabolic role of GH in normally statured adults with childhood-onset GHD and in those with acquired GHD, taking into account the well recognized heterogeneity of the adult GHD syndrome.

The double contact phase in walking children

“…A Froude speed of 0.5 is approximately the speed at which people and animals spontaneously change from a walk to a run or trot, as shown for differently sized subjects, i.e. children (Cavagna et al, 1983), for males and females (Herljac, 1995), for pygmies (Minetti et al, 1994), for short stature growth-hormone-deficiency patients (Minetti et al, 2000) and for different species (Alexander, 1989). Although it is possible to walk at Froude speeds up to 1.0 (Fig.·7), higher speeds require a different gait.…”

Development of pendulum mechanism and kinematic coordination from the first unsupported steps in toddlers

“…Subjects with a dynamically similar locomotion are expected to output comparable values of mechanical power when walking with the same Fr. Thus, children between 2 and 12 years of age (Cavagna et al, 1983;Schepens et al, 2004), adult Pygmies (Minetti et al, 1994) and dwarfs (Minetti et al, 2000) have the same percentage of recovery R (Equation·7) of mechanical energy as normal-sized adults when they walk at the same Fr value. Typically, R peaks at Ϸ65% at Fr Ϸ0.3, and falls off at lower and higher Fr values (see fig.·10 in Saibene and Minetti, 2003).…”

“…Fr is directly proportional to the ratio between the kinetic energy and the gravitational potential energy needed during movement. Dynamic similarity implies that the recovery of mechanical energy in subjects of short height, such as children (Cavagna et al, 1983;Schepens et al, 2004), Pygmies (Minetti et al, 1994) and dwarfs (Minetti et al, 2000), is not different from that of normal sized adults at the same Fr. No overt violations of the pendulum mechanism have been reported so far for legged walking on land.…”

Changes in the Limb Kinematics and Walking-Distance Estimation After Shank Elongation: Evidence for a Locomotor Body Schema?

“…The corresponding Froude number was 0.23 Ϯ 0.03, thus being similar to that expected from the characteristic length of his legs (L). Indeed, Fr ϭ 0.25 corresponds to an optimal walking speed (optimal exchange between potential and kinetic energies of the center-of-body mass) and typically reflects self-selected speed both in normalsized adults and in subjects of short height, such as children, pygmies, and dwarfs (Cavagna et al 1983;Minetti 2000). In contrast, after surgery, ACH walked more slowly at all selfselected speeds (Table 1), even though his limb length increased considerably: for instance, mean normal walking speed decreased to 2.04 Ϯ 0.22 km/h and the corresponding Froude number was also lower (Fr ϭ 0.06 Ϯ 0.01).…”