Complex sentence: The number of additional motor units recruited during a given increment in force declines sharply at high levels of voluntary force, suggesting that even though high threshold units generate more tension, the contribution of recruitment to increase voluntary force declines at higher force levels.
Split into simpler sentences: The number of additional motor units recruited during a given increment in force declines sharply at high levels of voluntary force. This suggests that even though high threshold units generate more tension, the contribution of recruitment to increase voluntary force declines at higher force levels.