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Cited by 11Muscle Physiology and DisordersMuscle metabolism and nutritionExercise and Physiological Responses

Phytoecdysteroids Accelerate Recovery of Skeletal Muscle Function Following in vivo Eccentric Contraction-Induced Injury in Adult and Old Mice

Open access
Zwetsloot, Kevin A., Shanely, R. Andrew, Godwin, Joshua S., Hodgman, Charles F.·2021·Frontiers in Rehabilitation Sciences
DOI 10.3389/fresc.2021.757789PMC PMC9397830
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Abstract

Background: Eccentric muscle contractions are commonly used in exercise regimens, as well as in rehabilitation as a treatment against muscle atrophy and weakness. If repeated multiple times, eccentric contractions may result in skeletal muscle injury and loss of function. Skeletal muscle possesses the remarkable ability to repair and regenerate after an injury or damage; however, this ability is impaired with aging. Phytoecdysteroids are natural plant steroids that possess medicinal, pharmacological, and biological properties, with no adverse side effects in mammals. Previous research has demonstrated that administration of phytoecdysteroids, such as 20-hydroxyecdysone (20E), leads to an increase in protein synthesis signaling and skeletal muscle strength. Methods: To investigate whether 20E enhances skeletal muscle recovery from eccentric contraction-induced damage, adult (7–8 mo) and old (26–27 mo) mice were subjected to injurious eccentric contractions (EC), followed by 20E or placebo (PLA) supplementation for 7 days. Contractile function via torque-frequency relationships (TF) was measured three times in each mouse: pre- and post-EC, as well as after the 7-day recovery period. Mice were anesthetized with isoflurane and then electrically-stimulated isometric contractions were performed to obtain in vivo muscle function of the anterior crural muscle group before injury (pre), followed by 150 EC, and then again post-injury (post). Following recovery from anesthesia, mice received either 20E (50 mg•kg−1 BW) or PLA by oral gavage. Mice were gavaged daily for 6 days and on day 7, the TF relationship was reassessed (7-day). Results: EC resulted in significant reductions of muscle function post-injury, regardless of age or treatment condition (p < 0.001). 20E supplementation completely recovered muscle function after 7 days in both adult and old mice (pre vs. 7-day; p > 0.05), while PLA muscle function remained reduced (pre vs. 7-day; p < 0.01). In addition, histological markers of muscle damage appear lower in damaged muscle from 20E-treated mice after the 7-day recovery period, compared to PLA. Conclusions: Taken together, these findings demonstrate that 20E fully recovers skeletal muscle function in both adult and old mice just 7 days after eccentric contraction-induced damage. However, the underlying mechanics by which 20E contributes to the accelerated recovery from muscle damage warrant further investigation.

AI snapshot

Written from the paper’s full text.

TL;DR

Daily oral 20-hydroxyecdysone (20E) for 7 days fully restored in vivo contractile function after eccentric contraction-induced muscle injury in both adult and old mice, whereas placebo-treated mice remained impaired. The study reports accelerated functional recovery without identifying the underlying mechanism.

Key findings

  • Eccentric contractions caused a ~40–50% decline in maximal isometric torque of the anterior crural muscles immediately post-injury, regardless of age or treatment (p < 0.001).
  • 20E supplementation (50 mg·kg−1 body mass daily for 7 days) completely recovered muscle function in adult and old mice (pre vs. 7-day, p > 0.05), while placebo-treated muscle function remained reduced (pre vs. 7-day, p < 0.01).
  • Maximal tetanic torque recovered only in 20E-treated adult and old mice; twitch torque remained lower at 7 days in all groups (p = 0.032), and EC50 remained different from pre-injury at 7 days (p = 0.009).
  • Histological muscle damage scores were ≤1.0 on a 0–3 scale at 7 days post-injury; PLA-treated groups appeared to have higher scores than 20E-treated groups, with old PLA mice appearing to have the greatest damage score.

Methods

  • Male C57BL/6 adult (7–8 months; PLA n = 4, 20E n = 7) and old (26–27 months; PLA n = 7, 20E n = 7) mice underwent 150 eccentric contractions of the anterior crural muscle group, then received 20E (50 mg·kg−1 body mass) or placebo by oral gavage daily for 7 days.
  • In vivo contractile function was measured by torque-frequency relationships three times per mouse: pre-injury, immediately post-injury, and after 7-day recovery; separate sham-treated adult and old groups (n = 10 each) served as controls.
  • Analyses used repeated measures factorial ANOVA with Fisher’s LSD post-hoc tests; torque-frequency data were also modeled with a four-parameter logistic fit to derive EC50. Histological damage was assessed qualitatively on a 0–3 scale, with no statistical analysis performed on damage scores.

Limitations

  • The authors state that only a single recovery time point and a short 7-day period were measured, making it difficult to forecast how long placebo-treated mice would have taken to recover.
  • The authors state that they did not assess immune cells or inflammatory mechanisms, have no direct evidence that phytoecdysteroids influence inflammation during recovery, and cannot conclude whether 20E benefits muscle damage markers or tissue remodeling; no analyses were performed on Gomori trichrome-stained sections.
  • Evident from the text: the adult placebo group was small (n = 4), only male mice were studied, histological damage scoring was qualitative/semi-quantitative without statistical analysis, and no mechanistic protein synthesis or signaling measures were reported.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.3389/fresc.2021.757789

Cites

65 of 65 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 61 cited sources checked · 0 supported · 0 flagged

  • Findingown data

    TA and EDL muscle mass normalized to body mass were significantly lower in old mice regardless of treatment.

    “TA and EDL muscle mass (normalized to body mass; mg•g−1) were significantly lower in the old mice (main effect of age, p = 0.003 for both TA and EDL), regardless of treatment (treatment x age interaction, p = 0.453 for TA and p = 0.326 for EDL).”
    Quote in the paperNot a substantial claim
  • Findingown data

    The eccentric contraction-induced muscle damage protocol results in a ~40-50% decline in anterior crural muscle group contractile function, measured by maximal isometric torque, regardless of age or treatment condition.

    “EC resulted in significant reductions of muscle function post-injury, regardless of age or treatment condition (p < 0.001).”
    • Also stated in: § Eccentric Contraction-Induced Muscle Damage · plain
      “The eccentric contraction-induced muscle damage protocol results in a ~40–50% decline (main effect of time, p < 0.001) in anterior crural muscle group contractile function, measured by maximal isometric torque (Figure 1).”
    • Also stated in: § In vivo Contractile Function Testing and Eccentric Contraction-Induced Damage Protocol · plain
      “There was a significant 40–50% decline in isometric torque after the 150-eccentric contraction muscle damage protocol, regardless of age or treatment condition.”
    Quote in the paperSubstantial claim
  • Findingcitation

    Functional capacity is significantly impaired immediately and for several days after 150 eccentric contractions.

    “Here in this study, as with many others (34, 35, 42–44), we reaffirm that functional capacity is significantly impaired immediately, and for several days after, 150 eccentric contractions.”
    Quote in the paperSubstantial claim0 of 5 sources checked
    • cites [34] Lowe, 1995, Muscle function and protein metabolism after initiation of eccentric contraction-induced injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [35] Corona, 2008, FKBP12 deficiency reduces strength deficits after eccentric contraction-induced muscle injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [42] Ingalls, 1998, Dissociation of force production from MHC and actin contents in muscles injured by eccentric contractions, J Muscle Res Cell Motil. source

      Not checked in the free run.

    • cites [43] Warren, 1996, Estradiol effect on anterior crural muscles-tibial bone relationship and susceptibility to injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [44] Rathbone, 2003, Importance of satellite cells in the strength recovery after eccentric contraction-induced muscle injury, Am J Physiol Regul Integr Comp Physiol. source

      Not checked in the free run.

  • Findingown data

    20E supplementation completely recovered muscle function after 7 days in both adult and old mice.

    “20E supplementation completely recovered muscle function after 7 days in both adult and old mice (pre vs. 7-day; p > 0.05)”
    • Also stated in: § In vivo Skeletal Muscle Contractile Function · plain
      “20E treatment resulted in full recovery of isometric torque at 7 days-post eccentric damage in both adult and old mice”
    • Also stated in: § Abstract · plain
      “20E fully recovers skeletal muscle function in both adult and old mice just 7 days after eccentric contraction-induced damage.”
    Quote in the paperSubstantial claim
  • Findingown data

    There were no differences in the loss of contractile function in response to eccentric damage between ages of mice or treatment groups.

    “Additionally, there were no differences in the loss of contractile function in response to eccentric damage between ages of mice or treatment groups (time x treatment x age interaction, p = 0.740).”
    Quote in the paperNot a substantial claim
  • May combine two claims. 21
  • Classified as probably not a substantial claim. 20

  • May combine two claims.

    Findingown data

    Twitch torque was significantly lower in all treatment groups and ages immediately after eccentric damage and remained lower at 7 days compared to pre-damage.

    “twitch was significantly lower in all treatment groups and ages immediately after eccentric damage (p < 0.001) and remained lower at 7 days (p = 0.032; Figures 3A,E, respectively), compared to pre-damage.”
    • Also stated in: § In vivo Skeletal Muscle Contractile Function · plain
      “Analysis revealed significant reductions in twitch torque (20 Hz; A,E) in all groups immediately after (Post) and at 7 days (7-d) following the eccentric contraction-induced muscle damage protocol, regardless of treatment condition.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    EC50 was significantly higher in all age and treatment groups immediately post-damage, and at 7 days it remained significantly different from both pre and post time points.

    “EC50 was significantly higher in all age and treatment groups immediately post-damage (p < 0.001), before beginning to return back to pre-damage levels by 7 days of recovery, i.e., there was still a significant difference between 7-d vs. Pre (p = 0.009), but also a difference between 7-d vs. Post (p = 0.002) time points”
    • Also stated in: § In vivo Skeletal Muscle Contractile Function · plain
      “EC50 was significantly higher in all age and treatment groups at Post, but EC50 at 7-d was still significantly different than Post and Pre (D,H).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    There were no age- or treatment-related differences regarding how eccentric damage caused muscle contractile dysfunction or recovery from muscle damage; adult and old mice displayed similar responses to eccentric muscle damage and recovery with 20E treatment.

    “Furthermore, there were no age- or treatment-related differences regarding how eccentric damage caused muscle contractile dysfunction or recovery from muscle damage (all treatment x age interactions, p > 0.500). In other words, adult and old mice displayed similar responses to eccentric muscle damage and recovery with 20E treatment.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data

    Twitch to tetanic ratio was significantly lower in all groups immediately after eccentric damage but recovered with 7 days of recovery.

    “the ratio was significantly lower in all groups immediately after eccentric damage (Figures 3C,G), but recovered with 7 days of recovery (time × treatment × age interaction, p = 0.630).”
    • Also stated in: § In vivo Skeletal Muscle Contractile Function · plain
      “Twitch:Tetanic ratio was significantly reduced at Post in both adult (C) and old mice (G), regardless of treatment condition, compared to Pre, but Twitch:Tetanic recovered by 7-d.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data

    Maximal tetanic torque was significantly lower immediately after eccentric damage in all treatment groups and ages; only the 20E-treated groups in both adult and old mice fully recovered maximal tetanic torque to pre-damage levels at 7 days.

    “Maximal tetanic torque was significantly lower immediately after eccentric damage in all treatment groups and ages (p < 0.001); however, only the 20E-treated groups in both adult (Figure 3B) and old mice (Figure 3F) fully recovered maximal tetanic torque by returning to pre-damage levels at 7 days of recovery.”
    • Also stated in: § In vivo Skeletal Muscle Contractile Function · plain
      “Only the 20E-treated adult and old mice fully recovered maximal tetanic torque to pre-injury levels by 7-d.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingcitation

    Declines in functional capacity with eccentric contractions were similar between adult and old mice and between treatments.

    “Consistent with previous studies in rodents (45, 46), these declines in functional capacity with eccentric contractions were similar between the adult and old mice and between treatments.”
    • Also stated in: § Discussion · plain
      “In other words, all mice in this study sustained similar degrees of muscle damage, regardless of age or treatment.”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [45] McBride, 1995, Prolonged recovery and reduced adaptation in aged rat muscle following eccentric exercise, Mech Ageing Dev. source

      Not checked in the free run.

    • cites [46] Brooks, 1990, Contraction-induced injury: recovery of skeletal muscles in young and old mice, Am J Physiol. source

      Not checked in the free run.

  • May combine two claims.

    Findingcitation

    The novel observation that 20E treatment fully recovers skeletal muscle function in just 7 days after eccentric damage is much earlier than other studies using similar eccentric damage protocols in mice.

    “The novel observation that 20E treatment fully recovers skeletal muscle function in just 7 days after eccentric damage is much earlier than other studies using similar eccentric damage protocols in mice (34, 35, 42, 47).”
    Quote in the paperSubstantial claim0 of 4 sources checked
    • cites [34] Lowe, 1995, Muscle function and protein metabolism after initiation of eccentric contraction-induced injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [35] Corona, 2008, FKBP12 deficiency reduces strength deficits after eccentric contraction-induced muscle injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [42] Ingalls, 1998, Dissociation of force production from MHC and actin contents in muscles injured by eccentric contractions, J Muscle Res Cell Motil. source

      Not checked in the free run.

    • cites [47] Ingalls, 1998, E-C coupling failure in mouse EDL muscle after in vivo eccentric contractions, J Appl Physiol. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    The ages of the adult mice in this study were equivalent to 30-35 year-old humans, while the old mice were equivalent to 70-75 year-old humans.

    “The ages of the adult mice in this study were the equivalent of 30–35 year-old humans, while the old mice were the equivalent of 70–75 year-old humans (9).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [9] Tidball, 2021, Aging of the immune system and impaired muscle regeneration: a failure of immunomodulation of adult myogenesis, Exp Gerontol. source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductnone given

    Mice were randomly assigned to either the placebo control treatment group or the 20-hydroxyecdysone treatment group.

    “Mice were randomly assigned to either the placebo control treatment group (PLA) or the 20-hydroxyecdysone treatment group (20E) and received the first treatment via oral gavage.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    20E is considered anabolic, but non-androgenic since it does not increase prostate or seminal vesicle mass in young castrated rats after 10 days of treatment, nor does it alter organ or testes mass in aging mice with 28 days of treatment.

    “Thus, 20E is considered anabolic, but non-androgenic since it does not increase prostate or seminal vesicle mass in young castrated rats after 10 days of treatment (30), nor does it alter organ or testes mass in aging mice with 28 days of treatment (31).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [30] Syrov, 2000, Comparative experimental investigation of the anabolic activity of phytoecdysteroids and steranabols, Pharm Chem J. source

      Not checked in the free run.

    • cites [31] Lawrence, 2021, Phytoecdysteroids do not have anabolic effects in skeletal muscle in sedentary aging mice, Int J Environ Res Public Health. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    28 days of 20E treatment does not alter muscle mass or fiber size, nor does a single acute treatment of 20E stimulate anabolic signaling in skeletal muscle tissue from sedentary aging C57BL/6 mice.

    “Conversely, we recently reported that 28 days of 20E treatment does not alter muscle mass or fiber size, nor does a single acute treatment of 20E stimulate anabolic signaling in skeletal muscle tissue from sedentary aging C57BL/6 mice (31).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [31] Lawrence, 2021, Phytoecdysteroids do not have anabolic effects in skeletal muscle in sedentary aging mice, Int J Environ Res Public Health. source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data

    Separate groups of sham-treated adult and old mice were utilized as experimental controls.

    “Additionally, separate groups (n = 10/each) of sham-treated adult and old mice were utilized as experimental controls.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    20E has been reported to increase grip strength in young rats and stimulate protein synthesis via the PI3K/Akt pathway in C2C12 myotubes in vitro.

    “Regarding skeletal muscle, 20E has been reported to increase grip strength in young rats and stimulate protein synthesis via the PI3K/Akt pathway in C2C12 myotubes in vitro (32).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [32] Gorelick-Feldman, 2008, Phytoecdysteroids increase protein synthesis in skeletal muscle cells, J Agric Food Chem. source

      Not checked in the free run.

  • May combine two claims.

    Study design and conductown data

    In vivo skeletal muscle contractile function was not altered over time or treatment in any adult or old sham-treated groups, demonstrating repeatability of the experimental procedures.

    “In vivo skeletal muscle contractile function was not altered over time or treatment in any of the adult or old sham-treated groups (time × treatment × age interaction, p = 0.766), thus demonstrating the repeatability of our experimental procedures (Supplementary Figure 1).”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Phytoecdysteroids possess medicinal, pharmacological, and biological properties, with no adverse side effects in mammals.

    “PEs possess a plethora of medicinal, pharmacological, and biological properties, with no adverse side effects in mammals (26, 27).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [26] Israili, 2009, Ethnopharmacology of the plants of genus Ajuga, Pakistan J Pharm Sci.

      Not checked in the free run.

    • cites [27] Das, 2020, The phytochemical, biological, and medicinal attributes of phytoecdysteroids: an updated review, Acta Pharmaceutica Sinica B. source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Premisecitation

    Warren et al. previously reported that decreases in isometric torque during this eccentric contraction-induced muscle damage protocol are the result of muscle injury, not fatigue.

    “Warren et al. previously reported that decreases in isometric torque during this eccentric contraction-induced muscle damage protocol are the result of muscle injury, not fatigue (36).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [36] Warren, 1999, Uncoupling of in vivo torque production from EMG in mouse muscles injured by eccentric contractions, J Physiol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Skeletal muscle possesses the remarkable ability to repair and regenerate after injury or damage; however, this ability is impaired with aging.

    “Skeletal muscle possesses the remarkable ability to repair and regenerate after an injury or damage; however, this ability is impaired with aging (4–7).”
    Quote in the paperSubstantial claim0 of 4 sources checked
    • cites [4] Brooks, 1988, Contractile properties of skeletal muscles from young, adult and aged mice, J Physiol. source

      Not checked in the free run.

    • cites [5] Gutmann, 1976, Regeneration and transplantation of muscles in old rats and between young and old rats, Life Sci. source

      Not checked in the free run.

    • cites [6] Carlson, 1989, Muscle transplantation between young and old rats: age of host determines recovery, Am J Physiol. source

      Not checked in the free run.

    • cites [7] Carlson, 1996, The regeneration of noninnervated muscle grafts and marcaine-treated muscles in young and old rats, J Gerontol A Biol Sci Med Sci. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    Body mass did not differ between any treatment group.

    “Body mass did not differ between any treatment group (time x treatment x age interaction, p = 0.875); however, all groups lost body mass between initial and the 7-day recovery time point (main effect of time, p = 0.008).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    The greatest declines in muscle function occur immediately following eccentric contraction-induced injury, yet markers of muscle damage are not fully apparent until 1-2 days after injury.

    “Recall that the greatest declines in muscle function occur immediately following eccentric contraction-induced injury, yet markers of muscle damage are not fully apparent until 1–2 days after injury (34, 47, 52).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [34] Lowe, 1995, Muscle function and protein metabolism after initiation of eccentric contraction-induced injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [47] Ingalls, 1998, E-C coupling failure in mouse EDL muscle after in vivo eccentric contractions, J Appl Physiol. source

      Not checked in the free run.

    • cites [52] Clarkson, 1992, Muscle function after exercise-induced muscle damage and rapid adaptation, Med Sci Sports Exerc. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    20E stimulates protein synthesis primarily through activation of PI3K/Akt signaling in a dose-dependent manner in C2C12 myotubes in vitro.

    “Gorelick-Feldman et al. demonstrated that 20E stimulates protein synthesis (32), primarily through the activation of PI3K/Akt signaling (29), in a dose-dependent manner in C2C12 myotubes in vitro.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [32] Gorelick-Feldman, 2008, Phytoecdysteroids increase protein synthesis in skeletal muscle cells, J Agric Food Chem. source

      Not checked in the free run.

    • cites [29] Gorelick-Feldman, 2010, Ecdysteroids elicit a rapid Ca2+ flux leading to Akt activation and increased protein synthesis in skeletal muscle cells, Steroids. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    EC coupling dysfunction is responsible for 57-75% of the functional loss of muscle strength acutely after eccentric contractions.

    “It has been estimated that EC coupling dysfunction is responsible for 57–75% of the functional loss of muscle strength acutely after eccentric contractions (51).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [51] Warren, 2002, What mechanisms contribute to the strength loss that occurs during and in the recovery from skeletal muscle injury?, J Orthop Sports Phys Ther. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    This recovery process may take longer depending on the severity of damage incurred.

    “But this process may take longer depending on the severity of damage incurred (48).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [48] Howell, 1993, Muscle stiffness, strength loss, swelling and soreness following exercise-induced injury in humans, J Physiol. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Brooks and Faulkner demonstrated that young and aged mice respond similarly to eccentric damage, but young mice recovered muscle function by 4 weeks whereas aged mice had not.

    “Seminal work by Brooks and Faulkner (46) demonstrated that while young and aged mice respond similarly to eccentric damage (i.e., loss of strength and markers of muscle damage), young mice had recovered muscle function by 4 weeks post-damage, whereas aged mice had not.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [46] Brooks, 1990, Contraction-induced injury: recovery of skeletal muscles in young and old mice, Am J Physiol. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Skeletal muscle protein synthesis signaling, via activation of the mTORC1 pathway, is stimulated in the range of 1-7 days post-damage in response to various eccentric or lengthening contraction protocols in rodents and humans.

    “Skeletal muscle protein synthesis signaling, via activation of the mTORC1 pathway, is stimulated in the range of 1–7 days post-damage in response to various eccentric or lengthening contraction protocols in rodents and humans (57–61).”
    Quote in the paperNot a substantial claim0 of 5 sources checked
    • cites [57] Baumann, 2016, Recovery of strength is dependent on mTORC1 signaling after eccentric muscle injury, Muscle Nerve. source

      Not checked in the free run.

    • cites [58] Cuthbertson, 2006, Anabolic signaling and protein synthesis in human skeletal muscle after dynamic shortening or lengthening exercise, Am J Physiol Endocrinol Metab. source

      Not checked in the free run.

    • cites [59] Jameson, 2021, Reducing NF-kappaB signaling nutritionally is associated with expedited recovery of skeletal muscle function after damage, J Clin Endocrinol Metab. source

      Not checked in the free run.

    • cites [60] Moore, 2005, Myofibrillar and collagen protein synthesis in human skeletal muscle in young men after maximal shortening and lengthening contractions, Am J Physiol Endocrinol Metab. source

      Not checked in the free run.

    • cites [61] Pavis, 2021, Improved recovery from skeletal muscle damage is largely unexplained by myofibrillar protein synthesis or inflammatory and regenerative gene expression pathways, Am J Physiol Endocrinol Metab. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Disruptions to sarcomeric and sarcolemmal structures have been observed within days of the eccentric exercise bout.

    “As the normal progression of damage and regeneration processes occur, disruptions to sarcomeric (contractile apparatus) and sarcolemmal (membrane) structures have been observed within days of the eccentric exercise bout (35, 55, 56).”
    Quote in the paperNot a substantial claim0 of 3 sources checked
    • cites [35] Corona, 2008, FKBP12 deficiency reduces strength deficits after eccentric contraction-induced muscle injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [55] Newham, 1983, Ultrastructural changes after concentric and eccentric contractions of human muscle, J Neurol Sci. source

      Not checked in the free run.

    • cites [56] Friden, 1983, Myofibrillar damage following intense eccentric exercise in man, Int J Sports Med. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    Pre-treatment of myotubes with Bordetella pertussis toxin abolishes the 20E effect on Ca+2 influx and Akt activation, suggesting that 20E functions through a G protein-coupled cell surface receptor.

    “Furthermore, pre-treatment of myotubes with the G protein inhibitor, Bordetella pertussis toxin (PTX), abolishes the 20E effect on Ca+2 influx and Akt activation, suggesting that 20E functions through a G protein-coupled cell surface receptor (29).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [29] Gorelick-Feldman, 2010, Ecdysteroids elicit a rapid Ca2+ flux leading to Akt activation and increased protein synthesis in skeletal muscle cells, Steroids. source

      Not checked in the free run.

  • May combine two claims.

    Premisecitation

    The decreased twitch to tetanic ratio observed immediately after injury provides an indirect indication of EC coupling dysfunction with eccentric damage; however, this impairment was recovered by 7 days, regardless of treatment or age.

    “The decreased twitch to tetanic ratio observed immediately after injury provides an indirect indication of EC coupling dysfunction with eccentric damage; however, this impairment was recovered by 7 days, regardless of treatment or age (50, 54).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [50] Baumann, 2016, Utility of 17-(allylamino)-17-demethoxygeldanamycin treatment for skeletal muscle injury, Cell Stress Chaperones. source

      Not checked in the free run.

    • cites [54] Martin, 2004, Assessment of low-frequency fatigue with two methods of electrical stimulation, J Appl Physiol. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Warren et al. were the first to describe eccentric contraction-induced EC coupling dysfunction in mouse soleus muscle in vitro.

    “Warren et al. (53) were the first to describe eccentric contraction-induced EC coupling dysfunction in mouse soleus muscle in vitro.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [53] Warren, 1993, Excitation failure in eccentric contraction-induced injury of mouse soleus muscle, J Physiol. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Early functional loss of strength from eccentric contractions (0-5 days post-injury) is primarily the result of EC coupling dysfunction, not contractile structure disruption.

    “Studies from the past few decades have established that the early functional loss of strength from eccentric contractions (0–5 days post-injury) is primarily the result of EC coupling dysfunction, not contractile structure disruption.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductown data

    Based on only measuring a single time point and the relatively short recovery period (7 days), it is difficult to forecast how long placebo-treated mice would have taken to recover muscle function to pre-injury levels.

    “Based on only measuring a single time point and the relatively short recovery period examined in the current study (7 days), it is difficult to forecast just how long it would have taken for the placebo-treated mice in our study to recover muscle function back to pre-injury levels.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    One of the major complications with age-related impairment in muscle regeneration after injury is decreased myogenic potential and increased fibrogenesis.

    “One of the major complications with the age-related impairment in muscle regeneration after injury is not only the decreased myogenic potential, but also increased fibrogenesis (growth of connective tissue) (66).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [66] Zwetsloot, 2012, Differences in transcriptional patterns of extracellular matrix, inflammatory, and myogenic regulatory genes in myofibroblasts, fibroblasts, and muscle precursor cells isolated from old male rat skeletal muscle using a novel cell isolation procedure, Biogerontology. source

      Not checked in the free run.

  • Classified as probably not a substantial claim.

    Study design and conductown data

    If 20E is influencing connective tissue remodeling, it cannot be determined from our histological observations.

    “If 20E is influencing connective tissue remodeling, it cannot be determined from our histological observations.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Similar findings have been described previously wherein muscle function had recovered, but markers of muscle damage and regeneration, particularly centralized nuclei, are still visible weeks after eccentric contraction-induced muscle damage.

    “This is not surprising as similar findings have been described previously wherein muscle function had recovered, but markers of muscle damage and regeneration, particularly centralized nuclei, are still visible weeks after eccentric contraction-induced muscle damage (35, 44).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [35] Corona, 2008, FKBP12 deficiency reduces strength deficits after eccentric contraction-induced muscle injury, J Appl Physiol. source

      Not checked in the free run.

    • cites [44] Rathbone, 2003, Importance of satellite cells in the strength recovery after eccentric contraction-induced muscle injury, Am J Physiol Regul Integr Comp Physiol. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductnone given

    The animal study was reviewed and approved by the Appalachian State University Institutional Animal Care and Use Committee.

    “The animal study was reviewed and approved by the Appalachian State University Institutional Animal Care and Use Committee.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Premisecitation

    During regeneration of aged skeletal muscle, muscle tissue is replaced with connective tissue and consequently muscle function and muscle quality decline.

    “During regeneration of aged skeletal muscle, muscle tissue is replaced with connective tissue and, consequently muscle function and muscle quality decline.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [66] Zwetsloot, 2012, Differences in transcriptional patterns of extracellular matrix, inflammatory, and myogenic regulatory genes in myofibroblasts, fibroblasts, and muscle precursor cells isolated from old male rat skeletal muscle using a novel cell isolation procedure, Biogerontology. source

      Not checked in the free run.

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Premisenone given

    20-hydroxyecdysone (20E) possesses anabolic, anti-inflammatory, and antioxidant properties.

    “20-hydroxyecdysone (20E) possesses anabolic, anti-inflammatory, and antioxidant properties.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationnone given

    Much of the inflammatory/immune response contributing to muscle regeneration has run its course by 7 days post-eccentric injury and what remains is tissue remodeling and growth processes.

    “As described above, much of the inflammatory/immune response contributing to muscle regeneration has run its course by 7 days post-eccentric injury and what remains is tissue remodeling and growth processes.”
    Quote in the paperNot a substantial claim
37 of 37

  • The paper relies on this without support.

    No studies have assessed the functional characteristics of skeletal muscle after injury/damage with phytoecdysteroid treatment.

    “No studies have assessed the functional characteristics of skeletal muscle after injury/damage with phytoecdysteroid treatment.”

  • The paper relies on this without support.

    Regenerative capacity of skeletal muscle is impaired during aging, leading to prolonged or incomplete recovery from eccentric damage and further loss of muscle mass and strength.

    “The regenerative capacity of skeletal muscle is impaired during aging, and this can lead to prolonged or incomplete recovery from eccentric damage, as well as further loss of muscle mass and strength.”
    “However, the regeneration process is impaired with aging.”

  • The paper relies on this without support.

    Aged skeletal muscle displays anabolic resistance.

    “Moreover, since aged skeletal muscle displays anabolic resistance, 20E may be able to stimulate alternative anabolic pathways to those traditionally responsible for the anabolic resistance in aged muscle.”
3 of 3

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • 20E supplementation accelerated recovery of muscle integrity and function after eccentric exercise in mice.

    “In addition, 20E supplementation accelerated recovery of muscle integrity and function after eccentric exercise in mice.”

    From Molecular Targets of 20-Hydroxyecdysone in Mammals, Mechanism of Action: Is It a Calorie Restriction Mimetic and Anti-Aging Compound? (2025) · cites this paper as [21]

    The Results (In vivo Skeletal Muscle Contractile Function; page unavailable) show that 20E-treated adult and old mice recovered muscle function by day 7, while placebo-treated mice did not. The Results (Histology; page unavailable) say muscle damage scores only appeared lower with 20E; they do not establish accelerated recovery of muscle integrity as firmly as the claim states. (LLM, conf=0.86)

    Experimental — accuracy not yet measured

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • Claim of no treatment-related recovery differences conflicts with reported treatment effect

    Minor

    The text says there were no treatment-related differences in recovery, but elsewhere reports a significant time-by-treatment interaction and recovery in 20E-treated mice but not PLA-treated mice. A nonsignificant treatment-by-age interaction does not establish the absence of a treatment effect.

1 of 1

Cites

Flagged first, then by citations

Research works printed but not linked: 1

  1. Godwin, 2020, Whole-body heat shock accelerates recovery from impact-induced skeletal muscle damage in mice, Conditioning Medicine., 3, 184

Cited by

Sorted by citations

Related

Authors
Zwetsloot, K. A., Shanely, R. A., Godwin, J. S., & Hodgman, C. F.
Affiliations
Appalachian State University (US)
Corresponding author
Zwetsloot, Kevin A.
ORCID
Venue
Frontiers in Rehabilitation Sciences
Publisher
Frontiers Media SA
Published
2021-11-08
Volume
2
Pages
757789-757789
ISSN
2673-6861 (ISSN-L)
DOI
10.3389/fresc.2021.757789
PMC
PMC9397830
OpenAlex
W3211854257
Cited by
11
References
65
Citations by year
2026: 5 · 2025: 4 · 2023: 2
FWCI
0.16
Type
journal article
Language
en
Open access
Licence
Locations
  • Frontiers in Rehabilitation Sciences (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
Appalachian State University
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Muscle Physiology and Disorders
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Muscle metabolism and nutrition
  • Health Sciences › Medicine › Rehabilitation › Exercise and Physiological Responses
Keywords
phytoecdysteroids, 20-hydroxyecdysone, skeletal muscle recovery, muscle aging, muscle regeneration, muscle strength, exercise-related injuries, muscle atrophy, dietary supplementation, mice, rats, dogs, horses, cattle, pigs, sheep, goats

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-10.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-10.

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