Hamstrings Hypertrophy Is Specific to the Training Exercise: Nordic Hamstring versus Lengthened State Eccentric Training

Abstract

Introduction: The hamstring muscles play a crucial role in sprint running but are also highly susceptible to strain injuries, particularly within the biceps femoris long head (BFlh). This study compared the adaptations in muscle size and strength of the knee flexors, as well as BFlh muscle and aponeurosis size, after two eccentrically focused knee flexion training regimes: Nordic hamstring training (NHT) vs lengthened state eccentric training (LSET, isoinertial weight stack resistance in an accentuated hip-flexed position) vs habitual activity (no training controls: CON).

Methods: Forty-two healthy young males completed 34 sessions of NHT or LSET over 12 wk or served as CON ( n = 14/group). Magnetic resonance imaging-measured muscle volume of seven individual knee flexors and BFlh aponeurosis area, and maximum knee flexion torque during eccentric, concentric, and isometric contractions were assessed pre- and post-training.

Results: LSET induced greater increases in hamstrings (+18% vs +11%) and BFlh (+19% vs +5%) muscle volumes and BFlh aponeurosis area (+9% vs +3%) than NHT (all P ≤ 0.001), with no changes after CON. There were distinctly different patterns of hypertrophy between the two training regimes, largely due to the functional role of the muscles; LSET was more effective for increasing the size of knee flexors that also extend the hip (2.2-fold vs NHT), whereas NHT increased the size of knee flexors that do not extend the hip (1.9-fold vs LSET; both P ≤ 0.001). Changes in maximum eccentric torque differed only between LSET and CON (+17% vs +4%; P = 0.009), with NHT (+11%) inbetween.

Conclusions: These results suggest that LSET is superior to NHT in inducing overall hamstrings and BFlh hypertrophy, potentially contributing to better sprint performance improvements and protection against hamstring strain injuries than NHT.

FIGURE 1

Absolute changes (pre to post) in the volume of seven constituent knee flexor muscles following LSET (n = 14), NHT (n = 14), and control (CON, n = 11) interventions. Symbols indicate between-group differences in the magnitude of pre to post changes where post hoc tests displayed LSD P < 0.05: *different from CON, †different from LSET, §different from NHT. Data are means ± SE. Participant numbers are as stated previously other than the following: POP in LSET (n = 13); SAR, GRA, and POP in NHT (n = 13).

FIGURE 2

Absolute changes (pre to post) in the volume of anatomical and functional muscle groups following LSET (n = 14), NHT (n = 14), and control (CON, n = 11) interventions. Symbols indicate between-group differences in the magnitude of pre to post changes where post hoc tests displayed LSD P < 0.05: *different from CON, §different from NHT, †different from LSET. Data are means ± SE. Overall KF, the sum of all seven individual knee flexors. HAMS, the sum of the four hamstring muscles. KF and HE, the sum of BFlh, ST, and SM. KF not HE, the sum of BFsh, SAR, GRA, and POP. Participant numbers are as stated previously other than the following: overall KF and KF not HE in LSET and NHT (n = 13).

FIGURE 3

Summary of the percentage changes in muscle volume of the individual knee flexor muscles, and anatomical and functional muscle groups based on pre to post mean changes for each muscle or muscle group after LSET, NHT and control (CON) interventions. Symbols indicate between-group differences in the magnitude of pre to post changes where post hoc tests displayed LSD P < 0.05: *different from CON, §different from NHT, †different from LSET. KF, the sum of all seven individual knee flexors. HAMS, the sum of BFsh, BFlh, ST, and SM. KF and HE, the sum of BFlh, ST, and SM. KF not HE, the sum of BFsh, SAR, GRA, and POP.

FIGURE 4

Absolute changes (pre to post) in BFlh aponeurosis area (A) and maximum width (B) following lengthened state training (LSET, n = 14), NHT (n = 13), and control (CON, n = 11) interventions. Symbols indicate differences in the magnitude of pre to post changes where post hoc tests displayed LSD P < 0.05: *different from CON, §different from NHT. Data are means ± SE.

FIGURE 5

Absolute changes (pre to post) in maximum knee flexion torque and hamstring EMG during eccentric, concentric, and isometric contractions following lengthened state training (LSET, n = 14), NHT (n = 14), and control (CON, n = 14) interventions. Symbols indicate differences in the magnitude of pre to post changes where post hoc tests displayed LSD P < 0.05: *different from CON. Data are means ± SE.

FIGURE 6

Knee flexion maximum isometric torque–angle relationships pre and post (A) LSET (n = 14), (B) NHT (n = 14), and (C) control (CON, n = 14) interventions. D, Absolute changes (pre to post) in maximum knee flexion torque at knee joint angles from 35° to 95° (0° = full extension). A–C, Symbols denote significant within-group increases in torque from pre to post at the angle marked determined by paired t-tests as follows: *P < 0.05, **P < 0.01, or ***P < 0.001. Data are means ± SD. D, Symbols indicate differences in the magnitude of pre to post changes where post hoc tests displayed LSD P < 0.05: *different from CON, †different from LSET. Data are means ± SE.