Author(s): BJØRNSEN, T., ANDREASSEN, E.H., STENDAL, H., JENSEN, K.S., VÅRVIK, F.T., Institution: UNIVERSITY OF STAVANGER, Country: NORWAY, Abstract-ID: 2758

INTRODUCTION:
Strength training frequency is commonly manipulated to optimize strength and hypertrophic adaptations, yet its role when training volume is low remains unclear, particularly in applied team-sport settings during the competitive season. In-season football environments often allow only minimal supplemental strength training, and whether distributing such low training volumes across one or multiple weekly sessions influences neuromuscular and morphological adaptations is not well established. Therefore, the present study compared the effects of one versus two weekly lower-body strength training sessions, matched for total volume, on strength, jump and sprint performance, and muscle thickness adaptations in semi-professional football players.
METHODS:
Twentynine male football players (tier 2) were randomly allocated to perform either one (FREQ1; N= 15, 22.5±4.1 yrs; 78.2±11.2 kg) or two (FREQ2; N= 14, 22.9±4.0 yrs; 79.7±8.9 kg) weekly squat and leg extension training sessions while maintaining normal in-season football practice. During the 9-week intervention, FREQ1 completed 2 sets of squats and 2 sets of leg extension once weekly, whereas FREQ2 completed 1 set of each exercise twice weekly. All sessions were supervised, and all additional lower-body resistance training targeting the quadriceps and gluteal musculature was restricted. Pre- and post-intervention assessments included ultrasonography of muscle thickness (vastus lateralis at 40%, 50%, 60% of femur length, and gluteus maximus), 1RM squat, 1RM leg extension, countermovement jump (CMJ) height and sprint time.
RESULTS:
With no between-group differences, squat 1RM improved in FREQ1 by 12.0±7.1% (p<0.001) and in FREQ2 by 13.0±7.2% (p<0.001), whereas knee extension 1RM increased in FREQ1 by 13.6±13.0% (p<0.001) and in FREQ2 by 10.9±10.7% (p<0.001). Muscle thickness of gluteus maximus increased significantly more in FREQ2 (5.2±3.4%) compared with FREQ1 (−1.9±4.2%, p<0.001). With no significant group differences, vastus lateralis thickness in FREQ2 increased from baseline at 40% (FREQ2: 2.4±3.5%, p=0.03; FREQ1: 1.8±5.2%, p=0.28), whereas no significant changes were observed at 50% (FREQ1: 0.1±7.8%, p=0.86; FREQ2: 2.5±4.5%, p=0.06) and at 60% of femur length (FREQ1: 1.4±5.6%, p=0.38; FREQ2: 2.0±3.8%, p=0.12). CMJ height increased significantly more in FREQ2 (4.9±5.1%) compared with FREQ1 (0.6±4.4%, p=0.02). Sprint performance over 10 m and 20 m was significantly reduced by 4% in both FREQ1 and FREQ2.
CONCLUSION:
Distributing low-volume strength training across two weekly sessions appeared to favor adaptations in gluteus maximus muscle thickness and countermovement jump performance, while it did not affect improvements in maximal strength in semi-professional football players. These findings suggest that under low-volume in-season conditions, training frequency may have limited influence on strength development in the trained exercises, but may contribute to morphological adaptations that could transfer to explosive performance.