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|Title: ||Influence of rehydration on short-term recovery from prolonged running and subsequent exercise capacity in humans|
|Authors: ||Wong, Stephen H.S.|
|Issue Date: ||1996|
|Publisher: ||© S.H.S.Wong|
|Abstract: ||The aim of this research was to investigate the influence of rehydration with carbohydrate-electrolyte
solutions, during a short-tern recovery period, on hydration status, physiological responses, and
subsequent endurance capacity.
The first study (Chapter 4) examined whether prescribed or ad libitum rehydration with a
carbohydrate-electrolyte solution (CHO-E), during 4 h recovery from prolonged, submaximal running
would influence the subsequent endurance capacity. Five women and two men performed the
"recovery" protocol consisting of a 90 min run at 70%VO2 max on a level treadmill (TI) followed by
4 h rehydration-recovery (REC), and then an open-ended run to exhaustion at 70%VD2 max (1'2) as a
measure of their endurance capacity, on two occasions, at least 7 days apart. During the REC, subjects
were allowed to drink a 6.9% CHO-E ad libitum (AL) on one occasion. On the other occasion, the
volume of the same fluid was prescribed (PI) from calculations of the body mass lost during TI.
During T2, in the PI trial, the run time to exhaustion was 16% longer (P < 0.05) than during T2 in the
AL nial (69.9 ± 9.1 vs. 60.2 ± 10.2 min). Thus, ingestion of a prescribed volume of CHO-E after
prolonged exercise, calculated to replace the body fluid losses, restored endurance capacity to a greater
extent than ad libitum rehydration during the REC.
The second study (Chapter 5) investigated the influence of ingesting 50 g of carbohydrate (CHO)
immediately after exercise, either with subsequent serial CHO feeding or water ingestion during the
REC from prolonged, submaximal running on rehydration and subsequent endurance capacity. Eight
male subjects performed the "recovery" protocol [i.e. 90 min run at 70% V02 max (TI), 4 h
rehydration-recovery (REC), and open-ended run at 70% V02 max (T2)] on two occasions. During the
REC, subjects ingested a prescribed volume of fluid equal to the body mass lost during TI in both
conditions. Subjects ingested 50 g of CHO from a 6.9% CHO-E 15 min after TI on both occasions as
their first prescribed fluid intake. Thereafter, subjects drank either the same solution (CE) or water CW)
at each hour after TI during the REC. During T2, the run time to exhaustion was 54.2 ± 9.2 min in the
CE trial and 52.2 ± 6.2 min in the W trial, respectively (NS). The volume of fluid retained expressed as
a percentage of the volume ingested (% rehydration) during the CE trial was greater than that of the W
trial (CE: 73.5 ± 4.2% vs. W: 63.0 ± 5.7%; P < 0.05). Serial CHO feeding during the REC was
associated with increased CHO oxidation and suppressed fat oxidation during subsequent exercise.
Thus, ingesting -150 g of CHO in a 6.9% CHO-E over a 4 h period following prolonged running is
more effective in terms of rehydration compared to the same volume of fluid containing only 50 g of
CHO and water, but does not have a greater effect on subsequent endurance capacity.
The third study (Chapter 6) investigated the effects of rehydration per se and CHO ingestion, during
the REC, on subsequent endurance capacity. Nine male subjects performed the "recovery" protocol on
two occasions. During the REC, subjects drank either a 6.9% CHO-E (CE) or a CHO-free sweetened
placebo (PL) every 30 min after Tl up to the beginning of the 4 h of the REC. Volumes prescribed
(ml) were equal to 200% of the body mass lost during Tl. However, the total volume of fluid ingested
during the REC was only 170.8 ± 12.6% and 172.6 ± 13.8% of the body mass lost after Tl (NS).
During T2, in the CE trial, the run time to exhaustion was 54% longer (P < 0.01) than during T2 in the
PL trial (69.3 ± 5.5 vs. 45.0 ± 4.2 min). After the REC, subjects were in positive fluid balance by 423 ±
215 ml in the CE trial and 446 ± 239 ml in the PL trial (NS). Thus, positive fluid balance can be
achieved by ingesting a prescribed volume of either a 6.9% CHO-E or a placebo solution over the
REC, calculated to replace approximately 170% of the body fluid loss. Despite this similar hydration
status after the recovery in both conditions, ingesting a CHO-E is more effective in restoring endurance
capacity compared to the same volume of placebo solution.
The fourth study (Chapter 7) was intended to examine, and verify, the effects of ingesting different
amounts of CHO in the form of a CHO-E during the REC on rehydration and subsequent endurance
capacity. Nine male subjects performed the "recovery" protocol on two occasions. During the REC, a
fixed volume of fluid equivalent to 150% of the body mass lost during Tl was consumed. Subjects
ingested 50 g of CHO from a 6.5% CHO-E 30 min after Tl on both occasions as their first prescribed
fluid intake. Thereafter, subjects ingested either the same solution (CE) or a CHO-free sweetened
placebo (PL) every 30 min up to the beginning of the 4 h of the REC. During T2, the run times were
56.9 ± 8.1 min in the CE trial and 65.4 ± 7.8 min in the PL trial (NS). After the REC, subjects were
almost equally euhydrated (CE: 0 ± 184 ml; PL: -27 ± 120 ml) in both conditions (NS). Serial CHO
feeding over the REC was accompanied by enhanced CHO oxidation and suppressed fat oxidation. In
conclusion, ingesting a placebo solution containing 50 g of CHO and placebo over a 4 h period
following prolonged running, calculated to replace 150% of the body fluid loss, is equally effective in
achieving approximate euhydration and restoring endurance capacity compared to the same volume of
CHO-E containing -167 g of CHO.
The studies reported in this thesis suggest that in order to achieve euhydration during recovery, a
volume of fluid substantially larger (~ 150%) than that lost must be ingested. The provision of
additional CHO (-150 to 170 g) would be expected to restore the body's CHO stores to a greater extent
than a smaller amount of CHO (50 g) during the REC and, thereby, improve the subsequent endurance
capacity. However, this was not the case. It appears that the ingestion of large amounts of CHO, during
the REC, resulted in disturbances in fat and CHO metabolism which prevented an improvement in
endurance capacity during T2, after consumption of the additional CHO.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Information Science)|
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