Plasma lactic dehydrogenase activities in men during bed rest with exercise training

Area of Science:

• Exercise physiology
• Biochemistry

Background:

• Bed rest leads to deconditioning, affecting cardiorespiratory function and muscle metabolism.
• Lactic dehydrogenase (LDH) and its isoenzymes are key indicators of cellular stress and metabolic changes.

Purpose of the Study:

• To investigate the impact of different exercise regimens during bed rest on peak oxygen uptake (peak VO2) and LDH activity.
• To compare the effectiveness of isometric vs. isotonic exercise in mitigating bed rest-induced physiological changes.

Main Methods:

• Seven young men underwent three 2-week bed rest periods with intervening recovery.
• Participants engaged in isometric leg exercise, isotonic leg exercise, or no exercise for 1 hour daily.
• Peak VO2 and LDH isoenzyme activities were measured before, during, and after bed rest.

Main Results:

• All bed rest regimens reduced LDH-T by day 10, with the no-exercise group showing the earliest significant decrease.
• Peak VO2 decreased most with no exercise (12.3%), less with isotonic (9.2%), and least with isometric (4.8%).
• Isoenzyme increases were primarily in LDH-1 and LDH-2, regardless of exercise type.

Conclusions:

• Isometric exercise appears to better maintain skeletal muscle integrity and oxygen uptake capacity during bed rest compared to isotonic exercise.
• Despite exercise benefits, reduced hydrostatic pressure during bed rest ultimately impacts LDH-T levels, overriding exercise effects.