Quadriceps low-frequency fatigue and muscle pain are contraction-type-dependent

Abstract

Eccentric contractions are thought to induce greater low-frequency fatigue (LFF) and delayed-onset muscle soreness (DOMS) than concentric contractions. In this study we induced a similar amount of eccentric quadriceps muscle fatigue during either a concentric or eccentric fatigue task to compare LFF and DOMS. Subjects (n = 22) performed concentric or eccentric fatigue tasks using 75% of the pre-fatigue maximal voluntary contraction (MVC) torque, and both tasks ended when the MVC eccentric torque decreased by 25% pre-fatigue. When subjects reached the failure criterion during the eccentric and concentric tasks, the concentric MVC was 78 +/- 9.8% and 64 +/- 8.4% of initial, respectively. LFF was greater after the concentric than the eccentric protocols (22 +/- 12.4% and 15 +/- 7.6% increase, respectively; P < 0.01). DOMS was over 100% greater for the eccentric protocol. These results indicate that DOMS is not dependent on the events that contribute to LFF.

Figure 1

Representative data recorded during concentric (A) and eccentric (B) fatigue protocols. From the top, knee extension torque and knee angle are shown. The two horizontal lines “75% ECC MVC” and “75% CON MVC” are the target lines used in the protocols, each of which corresponds to 75% of pre-fatigue eccentric and concentric MVC torques, respectively. The solid and dotted torque lines indicate the torque recorded at the middle and end of the fatigue protocols. In the CON protocol (A), the subject performed repetitive, fatiguing 75% CON MVCs with single ECC MVCs performed periodically (only 1 for each is shown). The protocol was continued if the ECC MVCs exceeded the target torque, and this was the case even after the subject was not able to reach the target torque concentrically (the dotted line on the left). Similarly, in the ECC protocol (B), the subject performed 75% ECC contractions until the eccentric contraction torque fell to the 75% ECC MVC line (ECC contraction with a dotted line). After this contraction, one maximal concentric contraction (CON contraction with a dotted line) was recorded.

Figure 2

Changes in MVC torque for the two contraction types (concentric and eccentric contractions) in the two protocols (concentric and eccentric exercise protocols) at endpoint (EP) and 5 min (5 m) to 24 hr (24 h) post fatigue protocol as a percentage of respective pre-fatigue values. The arrow indicates the 25% reduction in eccentric torque as the criterion used to terminate the fatigue both the concentric and eccentric protocols. * indicates significant differences in the CON MVC torque between the two protocols.

Figure 3

Representative double pulse twitch (doublet; left) and single pulse twitch (right) torque elicited with the knee joint angle at 90° before (pre-fatigue) and after (30 s and 24 hr) the fatigue protocol. For clarity only 3 traces are shown, and the 3-s rest between twitch and doublet has been shortened.

Figure 4

Changes in twitch and doublet peak torque (A) and D/S ratio (B) before (Pre-fat) and immediately (30 s) to 24 hr (24 h) post fatigue in CON, ECC, and control protocols as an absolute torque (A) and as a percentage of respective pre-fatigue values (B). * indicates significant differences between the two protocols.

Figure 5

Mean maximal visual analog score at 24 and 48 hr post fatigue as an absolute distance in mm in the CON and ECC exercise protocols. * indicates significant differences between the two protocols.

Figure 6

A scatter plot showing the relationship between the D/S ratio measured 10 min post fatigue and the VAS score taken 24 h post fatigue in both CON and ECC exercise protocols. The best-fit lines with their r² values are presented for the two protocols.