Physiological responses to load carriage by backpack

Blacker, Sam D. (2009) Physiological responses to load carriage by backpack. Doctoral thesis, University of Southampton; University of Chichester.

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Abstract

Load carriage (19.3 Jan, 280 min, 31 kg load) in the field elicited a cardiovascular strain of 72 ± 5 %HRmax and caused neuromuscular impairment (7 ± 8% decrease in jump height (P0.05). The differences between conditions appeared to relate to changes in substrate oxidation, neuromuscular impairment and reduced mechanical efficiency. Neuromuscular function was measured in study 5 at 0, 24, 48 and 72 hours after the treadmill walking conditions described in study 4. L W caused no changes in neuromuscular function. Isometric knee extension force decreased immediately after LWLC (15 ± II %, P<0.05) and DWLC (16 ± 17 %, P<0.05), recovering by 72 hours for DWLC only. VA decreased after LWLC only, douhlet half relaxation time and 20:50Hz decreased after LWLC and DWLC (P<0.05). LWLC and DWLC were associated with decreases in isokinetic peak torque of knee, trunk extensors and flexors and shoulder flexors (P<0.05) with complete recovery by 72 hours. Regression models developed in study 6 indicated that participants with the most efficient metaholic and neuromuscular performance during 120 minutes of load carriage (25 kg backpack) on a level gradient had high body mass and high absolute V O, max with strong trunk, shoulder and knee flexors. To examine nutritional interventions to reduce the metabolic cost during, and neuromuscular impairment following, load carriage, participants consumed Placebo [PLA], Carbohydrate [CRO] or Whey Protein [PRO] beverages during 120 minutes ofload carriage and for three days of recovery. During load carriage (study 7), there were no differences in V 0,. RER, or EMG RMS between conditions at minute 5 (P>0.05). The increase in V 0, between 5 and 120 minutes was less during CRO (8 ± 5 %) than PLA (14 ± 6 %, P<0.05) or PRO (17 ± 4 %, P<0.05). RER decreased between minutes 5 and 120 during PLA and PRO only. Peak RMS did not change over time in In. rectus femoris, m. vastus latera/is, m. semitendinosus, and m. biceps femoris. Attenuation in V 02 drift during CRO could not entirely be accounted for by higher carbohydrate oxidation rates. During recovery, neuromuscular function was measured 0, 24, 48 and 72 hours after load carriage (study 8). There was no difference between PLA, CRO or PRO in the decrease in peak torque of knee and trunk extensors and flexors at 0 h. Peak torque of the knee extensors and flexors returned to pre-exercise values at 24 h during PRO followed by CHO at 48 hand PLA at 72 h (P>0.05). Trunk flexors returned to pre exercise value at 24 h for CHO and PRO but 48 h for PLA (P>0.05). Faster recovery of neuromuscular function was probably due to CRO and PRO improving protein balance, thus enhancing repair of muscle tissue damaged during exercise. In conclusion, load carriage increases V 0, and V O, drift whilst walking and causes neuromuscular impairment, which can last for up to 72 hours following exercise. Nutritional supplements can reduce V O,drift and improve the time course of recovery of neuromuscular function.

Item Type: Thesis (Doctoral)
Subjects: Q Science > QP Physiology
Divisions: Departments > Sport and Exercise Sciences
Related URLs:
Depositing User: Debbie Bogard
Date Deposited: 17 Jul 2013 13:40
Last Modified: 11 Aug 2017 11:26
URI: http://eprints.chi.ac.uk/id/eprint/820

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