Oxygen Consumption in Nonexercising Muscle after Exercise

Effects of robotic rehabilitation on walking and balance in pediatric patients with hemiparetic cerebral palsy

BACKGROUND

The most prominent characteristics of hemiparetic cerebral palsy (hCP) children are structural and functional asymmetries. These children have low walking speeds, endurance and poor balance. The robotic walking devices repeat and experience symmetrical stepping at the corresponding speed and angles of the lower extremities. RESEARCH QUESTION 1: Are robotic walking devices effective in the development of walking in hCP children who can walk? RESEARCH QUESTION 2: How does the aerobic exercise experience with assisted and symmetrical movement affect the walking and local muscle, peripheral oxygenation of children with hCP?

METHODS

This prospective, controlled study included 24 children with hCP. All children attended to a standard physiotherapy rehabilitation (PTR) program (three days a week for 12 weeks); those in the study group (n=12) also attended to an Robotic Gait Training (RGT) program three times a week. Evaluations performed before treatment, after treatment, and at the 3rd month after treatment included assessment of balance, functionality walking and measurements for oxygenation of vastus lateralis muscle and peripheral oxygenation.

RESULTS

The evaluations were similar for both groups before treatment. After treatment, walking speed, endurance and peripheral O2 saturation were increased and balance abilities and functional performances improved in the RGT group as compared with the pre-treatment evaluations; these improvements in balance and functional performance were generally preserved after 3 months of treatment. An increase in 6-min walking distance and a partial increase in gross motor functions and functional muscle strength were observed in the control group; however, these abilities were not preserved after the treatment.

SIGNIFICANCE

RGT can provide a faster and higher effect on the development of functional muscle strength, balance, walking speed and endurance than the standard PTR program. It improves functional walking performance. RGT can be used for aerobic exercise training in children with walking hCP.

Prolonged constant load cycling exercise is associated with reduced gross efficiency and increased muscle oxygen uptake

This study investigated the effects of prolonged constant load cycling exercise on cycling efficiency and local muscle oxygen uptake responses. Fourteen well-trained cyclists each completed a 2-h steady-state cycling bout at 60% of their maximal minute power output to assess changes in gross cycling efficiency (GE) and muscle oxygen uptake (mVO₂ ) at time points 5, 30, 60, 90, and 120 min. Near-infrared spatially resolved spectroscopy (NIRS) was used to continually monitor tissue oxygenation of the Vastus Lateralis muscle, with arterial occlusions (OCC) applied to assess mVO₂ . The half-recovery time of oxygenated hemoglobin (HbO₂ ) was also assessed pre and post the 2-h cycling exercise by measuring the hyperemic response following a 5-min OCC. GE significantly declined during the 2-h cycling bout (18.4 ± 1.6 to 17.4 ± 1.4%; P < 0.01). Conversely, mVO₂ increased, being significantly higher after 90 and 120 min than at min 5 (+0.04 mlO₂ /min/100 g; P = 0.03). The half-recovery time for HbO₂ was increased comparing pre and post the 2-h cycling exercise (+7.1 ± 19s), albeit not significantly (d: 0.48; P = 0.27). This study demonstrates that GE decreases during prolonged constant load cycling exercise and provides evidence of an increased mVO₂ , suggestive of progressive mitochondrial or contractile inefficiency.

Local muscle oxygen consumption related to external and joint specific power

The purpose of the present study was to examine the effects of external work rate on joint specific power and the relationship between knee extension power and vastus lateralis muscle oxygen consumption (mVO2). We measured kinematics and pedal forces and used inverse dynamics to calculate joint power for the hip, knee and ankle joints during an incremental cycling protocol performed by 21 recreational cyclists. Vastus lateralis mVO2 was estimated using near-infrared spectroscopy with an arterial occlusion. The main finding was a non-linear relationship between vastus lateralis mVO2 and external work rate that was characterised by an increase followed by a tendency for a levelling off (R(2)=0.99 and 0.94 for the quadratic and linear models respectively, p<0.05). When comparing 100W and 225W, there was a ∼43W increase in knee extension but still a ∼9% decrease in relative contribution of knee extension to external work rate resulting from a ∼47W increase in hip extension. When vastus lateralis mVO2 was related to knee extension power, the relationship was still non-linear (R(2)=0.99 and 0.97 for the quadratic and linear models respectively, p<0.05). These results demonstrate a non-linear response in mVO2 relative to a change in external work rate. Relating vastus lateralis mVO2 to knee extension power showed a better fit to a linear equation compared to external work rate, but it is not a straight line.

Effect of exercise intensity on oxygen consumption kinetics in non-exercising muscle during exercise

This study examined the effect of exercise intensity on the kinetics of muscle oxygen consumption in non-exercising forearm flexor muscles (VO(2mf)) during exercise. Seven healthy male subjects performed cycling exercise for 60 min at 30% of maximal oxygen consumption (%VO(2max)) and 30 min at 50% VO(2max) on separate days. The VO(2mf) values at rest and during exercise were measured by near-infrared spectroscopy. The VO(2mf) at 30% VO(2max) significantly increased to 1·2 ± 0·1-fold over resting value at 20 min after the beginning of exercise (P<0·05) and remained constant within 1·2- to 1·3-fold over resting value until 60 min during exercise. The VO(2mf) at 50% VO(2max) significantly increased to 1·2 ± 0·1-fold over resting value at 15 min after the beginning of exercise (P<0·05). Subsequently, the VO(2mf) at 50% VO(2max) increased with time to 1·3 ± 0·1-fold over resting value at 20 min after the beginning of exercise and to 1·5 ± 0·2-fold over resting value at 30 min. The VO(2mf) 15-30 min of exercise at 50% VO(2max) was significantly higher than that at 30% VO(2max) (P<0·05). These data suggest that the increase in VO(2mf) has a time lag from the beginning of exercise, and the kinetics of VO(2mf) during exercise differs with exercise intensity. Therefore, we conclude that the kinetics of VO(2mf) during exercise is dependent on exercise intensity.