Halvard Nikolai Grendstad

• Grendstad, Halvard & Hallén, Jostein (2023). Effects of adding high-intensity training during an 8-week period on maximal oxygen uptake in 12-year-old youth athletes. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. doi: 10.1111/sms.14489. Show summary

  Purpose: Maximal oxygen uptake (V̇O2max) increases during adolescence parallel to the increase in fat-free mass (FFM). How much endurance training adds to this effect is still controversial. Our aim was to investigate if inclusion of high-intensity training (HIT) during an 8-week training period was superior to low-intensity strength and coordination training in 12-year-old youth athletes concerning the effect on V̇O2max. Methods: Thirty-five cross-country skiers were randomized into a HIT group (ET) and a strength and coordination group (SC), while 29 less active peers served as controls for growth and maturation (C). Anthropometrics and V̇O2max were assessed before and after the training period, and level of physical activity and training were monitored with accelerometers, training logs and a questionnaire. Results: The number of weekly training sessions were higher for ET (4.6 ± 1.2) and SC (4.1 ± 1.0) compared with C (1.8 ± 2.0) (p < 0.01), with only ET conducting HIT sessions (1.9 ± 0.2 per week). C spent more time sedentary and less time in moderate and vigorous activity compared with ET (p < 0.05). All groups had a similar %-change pre-post in absolute V̇O2max (mL min−1) of 6% ± 6% for ET (p < 0.01), 5% ± 7 for SC (p = 0.14), and 5% ± 13% for C (p = 0.03), with no significant differences between groups. V̇O2max relative to FFM did not change significantly for any groups. Conclusion: The change in V̇O2max paralleled the change in FFM for all groups, questioning the effect of HIT on V̇O2max over an 8-week period in youth athletes.

• Gundersen, Hilde; Harris, Anette Kristoffersen; Grendstad, Halvard; Kristoffersen, Morten; Guttormsen, Atle & Dalen, Terje [Show all 7 contributors for this article] (2022). Performance in youth track and field is associated with birth quartile. A register-based study among athletes in Norway from 10 years to senior level. PLOS ONE. ISSN 1932-6203. 17(9). doi: 10.1371/journal.pone.0273472. Full text in Research Archive Show summary

  Introduction: Earlier studies have demonstrated that the oldest in a competition class are more likely to succeed than the youngest, a phenomenon called relative age effect (RAE). Track and field give us an opportunity to investigate the advantage of being born early in the year based upon actual performance, since objective criteria are the performance indicators. Hence, the aim of the present study was to investigate the occurrence of RAE in Norwegian track and field athletes in events where physical capacity is important for success. Methods: All individual season best results from the register of The Norwegian Athletics Federation (n = 28 999) obtained in all competition classes from the age of 10 years to senior in both sexes on 60m and 600m from 2011 to 2020 were downloaded. One-way ANOVA and LSD post hoc analyses were used to analyze performance differences according to birth quartiles between athletes. Further, odds ratios (OR) were used to calculate the odds of being among the top-100 for athletes for those born in the first quartile of the year compared to the last. Results: The RAE was present in several of the competition classes in sprint compared to middle-distance running, and in more male than female competition classes. Overall, the OR of being among the top-100 in one of the competition classes on 60m sprint when born in first quartile compared to last quartile was 2.88 [2.30–3.62] for males and 1.54 [1.26–1.89] for females. Conclusion: Being born early in the year in events with high demand for specific physical capacities is an advantage in both sexes in most of the youngest competition classes. In males, the advantage of being born early in the year lasted longer in sprint than in middle-distance running, indicating that puberty affects performance in sprint and middle-distance running differently.

• Gundersen, Hilde; Riiser, Amund; Algrøy, Erling Andre; Vestbøstad, Mona; Sæterbakken, Atle Hole & Clemm, Hege Synnøve Havstad [Show all 10 contributors for this article] (2022). Associations between biological maturity level, match locomotion, and physical capacities in youth male soccer players. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 32(11), p. 1592–1601. doi: 10.1111/sms.14225. Full text in Research Archive Show summary

  Introduction: Biological maturity level has shown to affect sport performance in youths. However, most previous studies have used noninvasive methods to estimate maturity level. Thus, the main aim of the present study was to investigate the association between skeletal age (SA) as a measure of biological maturation level, match locomotion, and physical capacity in male youth soccer players. Method: Thirty-eight Norwegian players were followed during two consecutive seasons (U14 and U15). Match locomotion was assessed with GPS-tracking in matches. SA, assessed by x-ray, physical capacities (speed, strength and endurance) and anthropometrics were measured in the middle of each season. Analysis of associations between SA, match locomotion, and physical capacities were adjusted for the potential confounding effect of body height and weight. Results: In matches, positive associations were found between SA and maximal speed and running distance in the highest speed zones. Further, SA was associated with 40 m sprint time and countermovement jump (CMJ) height, and with intermittent-endurance capacity after adjusting for body height (U14). Associations between SA and leg strength and power, and between SA and absolute VO2max were not significant after adjusting for body weight. There was no association between SA and total distance covered in matches. Conclusion: Biological maturity level influence match locomotion and performance on physical capacity tests. It is important that players, parents and coaches are aware of the advantages more mature players have during puberty, and that less mature players also are given attention, appropriate training and match competition to ensure proper development.

• Algrøy, Erling Andre; Grendstad, Halvard; Riiser, Amund; Nybakken, Tone; Sæterbakken, Atle Hole & Andersen, Vidar [Show all 7 contributors for this article] (2021). Motion analysis of match play in u14 male soccer players and the influence of position, competitive level and contextual variables. International Journal of Environmental Research and Public Health (IJERPH). ISSN 1661-7827. 18(14). doi: 10.3390/ijerph18147287. Full text in Research Archive
• Sæterbakken, Atle Hole; Haug, Vebjørn; Fransson, Dan; Grendstad, Halvard; Gundersen, Hilde & Moe, Vegard Fusche [Show all 10 contributors for this article] (2019). Match running performance on three different competitive standards in Norwegian soccer. Sports Medicine International Open. ISSN 2367-1890. doi: 10.1055/a-0943-3682. Full text in Research Archive
• Grendstad, Halvard Nikolai; Nilsen, Ann-Kristin; Rygh, Cecilie Brekke; Hafstad, Arild; Kristoffersen, Morten & Iversen, Vegard Vereide [Show all 11 contributors for this article] (2019). Physical capacity, not skeletal maturity, distinguishes competitive levels in male Norwegian U14 players. Scandinavian Journal of Medicine & Science in Sports. ISSN 0905-7188. 30(2), p. 254–263. doi: 10.1111/sms.13572. Full text in Research Archive Show summary

  The main aim of the present study was to compare skeletal maturity level and physi-cal capacities between male Norwegian soccer players playing at elite, sub-elite and non-elite level. Secondary, we aimed to investigate the association between skeletal maturity level and physical capacities. One hundred and two U14 soccer players (12.8-14.5 years old) recruited from four local clubs, and a regional team were tested for bone age and physical capacities. Bone age was estimated with x-ray of their left hand and used to indicate maturation of the skeleton. Players went through a com-prehensive test battery to assess their physical capacities. Between-groups analysis revealed no difference in chronological age, skeletal maturity level, leg strength, body weight, or stature. However, elite players were superior to sub-elite and non-elite players on important functional characteristics as intermittent-endurance ca-pacity (running distance: 1664 m ± 367 vs 1197 m ± 338 vs 693 m ± 235) and running speed (fastest 10 m split time: 1.27 seconds ± 0.06 vs 1.33 seconds ± 0.10 vs 1.39 seconds ± 0.11), in addition to maximal oxygen uptake (̇VO2max), standing long jump, and upper body strength (P < .05 for all comparisons). Medium-to-large correlations were found between skeletal maturity level and peak force (r = 695, P < .01), power (r = 684, P < .01), sprint (r = −.471, P<.001), and jump perfor-mance (r = .359, P < .01), but no correlation with upper body strength, ̇VO2max, or intermittent-endurance capacity. These findings imply that skeletal maturity level does not bias the selection of players, although well-developed physical capacity clearly distinguishes competitive levels. The superior physical performance of the highest-ranked players seems related to an appropriate training environment.

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• Grendstad, Halvard (2023). Skal puberteten bestemme våre neste idrettsutøvere? [Newspaper]. Dagsavisen.
• Grendstad, Halvard (2023). Trening i pubertet, kjøre på eller roe ned? [Radio]. Idrettsforskning.
• Grendstad, Halvard (2023). Kondisjonstrening i puberteten for idrettsaktiv ungdom.
• Grendstad, Halvard & Skattebo, Øyvind (2022). Puberty, more important for cardiovascular adaptations than endurance training? Journal of Physiology. ISSN 0022-3751. 600(11), p. 2817–2818. doi: 10.1113/JP283081.
• Grendstad, Halvard (2021). Hvordan trene i puberteten?
• Grendstad, Halvard (2021). Därför gör du rätt i att skippa konditionspassen under puberteten. Svensk Idrottsforskning: Organ för Centrum för Idrottsforskning. ISSN 1103-4629.
• Rygh, Cecilie Brekke; Vestbøstad, Mona; Grendstad, Halvard & Gundersen, Hilde (2019). Fotballers and skeletal maturity.
• Gundersen, Hilde; Grendstad, Halvard; Morland, Nicolay & Rygh, Cecilie Brekke (2019). Skader hos 14 år gamle fotballspillere.
• Grendstad, Halvard (2019). Fysisk kapasitet og skjelettmodning hos 14 år gamle fotballspillere selektert til å spille på ulike nivå.
• Grendstad, Halvard Nikolai; Rygh, Cecilie Brekke; Hafstad, Arild; Nilsen, Ann-Kristin; Nybakken, Tone & Gundersen, Hilde (2019). Skeletal maturation and physical performance of male youth soccer players selected to play at elite, sub-elite and non-elite level.
• Sæterbakken, Atle Hole; haug, Vebjørn; Franson, Dan; Grendstad, Halvard Nikolai; Gundersen, Hilde & Moe, Vegard Fusche [Show all 10 contributors for this article] (2019). The match running performance of players on three different competitive standards in Norwegian soccer.
• Grendstad, Halvard Nikolai (2016). Fysisk fotballform - hvordan kommer man seg dit på en trygg og god måte? Fotballtreneren. ISSN 0802-0906.
• Grendstad, Halvard Nikolai (2015). Tracking-systemer sin rolle i moderne fotball. Fotballtreneren. ISSN 0802-0906.
• Grendstad, Halvard Nikolai (2014). Exploring the relationship between match-related physical performance and injury - could modern match analysis contribute in injury prevention? NTNU.

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