Resistance exercise countermeasures for space flight: implications of training specificity

Area of Science:

• Exercise physiology
• Human physiology
• Biomechanics

Background:

• Unloading, such as bed rest, leads to significant muscle strength loss.
• Resistance exercise is a common countermeasure, but its effectiveness depends on training specificity.

Purpose of the Study:

• To investigate the training specificity of a constant load resistance exercise protocol.
• To determine if this protocol could prevent isokinetic strength detraining during 14 days of bed rest.

Main Methods:

• Twelve healthy men were assigned to either a no-exercise control group or a resistance exercise (REX) group.
• The REX group performed leg press exercises every other day for 14 days.
• Isokinetic knee extension testing (torque-velocity, torque-position, contractile work) was conducted before and after the bed rest period.

Main Results:

• Bed rest caused significant reductions in angle-specific torque (18%), average power (20%), torque-position relationship (24%), and total contractile work (27%).
• No significant group-by-time interactions were observed, indicating the REX protocol did not prevent strength losses.
• No significant interactions were found for velocity or mode (concentric/eccentric).

Conclusions:

• Bed rest rapidly induces substantial strength reductions.
• The constant load resistance exercise protocol used did not effectively preserve isokinetic strength.
• The discrepancy between closed-chain resistance training and open-chain isokinetic testing may be a key factor in the lack of protective effect.