To evaluate the effect of the extremes of long term high and low physical activities on musculoskeletal heath in middle age, a historical cohort study was performed. The MRI knee and back findings of 25 randomly selected subjects who were inducted into the armed forces in 1983 and served at least 3 years as elite infantry soldiers were compared 25 years later, with 20 randomly selected subjects who were deferred from army service for full time religious studies at the same time. Both cohorts were from the same common genome. The two primary outcome measures were degenerative lumbar disc disease evaluated by the Pfirrmann score and degenerative knee changes evaluated by the WORMS score. At the 25-year follow up, the mean Pfirrmann score (8.6) for the L1 to S1 level of the elite infantry group was significantly higher than that of the sedentary group (6.7), (
Degenerative changes in the lower back [
Elite infantry soldiers undergo long and demanding physical training and perform the most arduous of physical activities during their military service. They carry heavy loads on their backs and march and run long distances over varied terrain. They represent a population whose musculoskeletal system is subjected to extremely high and sustained loading [
We undertook a comparison study of the effect of the extremes of very high versus very low sustained musculoskeletal loading beginning at a young age on the musculoskeletal health of the lower back and knees at middle age using MRI. We compared a group of elite infantry soldiers who were under surveillance since the beginning of their military training in 1983 [
Military service is universal among the male Jewish population in Israel. At the age of 17, potential recruits are called up for a preinduction assessment. Each recruit is given a health profile based on a review of his prior medical history and a detailed physical examination. The profile is given along with codes of the specific health problems on which it is based. The profile is updated on an ongoing basis during the course of compulsory military service and afterwards during the period of reserve military service eligibility. Recruits with high profiles can serve in elite infantry units if they volunteer and pass physical and psychosocial tests.
In February 1983, 295 elite male Israeli infantry recruits who were participants in a prospective study of stress fractures began their infantry basic training [
During basic training, 31% of the recruits sustained stress fractures reflecting the difficulty of their training [
The health of the lower backs and knees of a group of soldiers from the 1983 study was compared to a control group of full time Torah scholars who were eligible for induction into the army in the period from 1981 to 1985 but never served in the military. These Torah scholars had army health profiles which allowed them to volunteer for elite combat units. The study was approved by the Ethics Committee of the Hadassah University Hospital and of the Israel Defense Forces Medical Corps and was registered with ClinicalTrials.gov (
A list of subjects from the 1983 study group who completed three years of compulsory military service as elite infantry soldiers and who continued to serve at least once a month for the next seventeen years in the military reserves was obtained from the Israeli Defense Forces. From this list of 51 subjects, 26 were randomly selected and contacted by the study’s senior author who served as their orthopedist in 1983 and were requested to participate in the study. The database from the 1983 study for these soldiers was preserved by the senior author of this study and was available for analysis.
A list of subjects from the Jerusalem region who received high health profiles, whose scheduled military induction in 1982–1985 was permanently deferred because they were Torah scholars and who continued to study Torah full time (≥12 hours per day) at least until the age of 25, was obtained from the Israeli Defense Forces. From this list of 52 subjects, 20 were randomly selected and contacted by a rabbi and asked to participate in the study.
Two subjects were evaluated biweekly between September 2007 and August 2008. After signing informed consent, each participant underwent the following assessments: a general questionnaire was administered orally, detailing military service, education, Torah studies, social economic status, medical history, orthopaedic injuries, and maternal and paternal origins (Ashkenazi or Sephardic). Current alcoholic consumption was assessed by recording the number of glasses of wine, beer, and hard liquor drunk weekly. The total intake was converted into units of eight ounces size with 14% alcoholic content. Smoking history was assessed by the lifetime pack years smoked. This was calculated by multiplying the number of packs of cigarettes smoked per day by the number of years the subject smoked. If the subject had changed smoking intensity, it was taken into account.
The questionnaire of Aadahl and Jørgensen [
The Israeli Army sports activity questionnaire in use since 1988 was orally administered to subjects to determine what sport activities they had participated in continuously for the previous five years and for how many hours each week. If the sports activity was not continuous over the previous five years, it was not recorded.
Height and weight were measured on a doctor’s balance scale (Detecto, Webb City, MO), and the body mass index was calculated.
An MRI was taken of the spine (T10-S1) using a Siemens 3T Trio MRI (Erlangen, Germany). The results were read by a single neuroradiologist. Disk degeneration was scored based on the criteria of Pfirrmann [
The Pfirrmann score for disc degeneration.
Grade | Structure | Distinction of nucleus and anulus | Signal intensity | Height of intervertebral disc |
---|---|---|---|---|
I | Homogeneous, bright white | Clear | Hyperintense, isointense to cerebrospinal fluid | Normal |
II | Inhomogeneous with or without horizontal bands | Clear | Hyperintense, isointense to cerebrospinal fluid | Normal |
III | Inhomogeneous, gray | Unclear | Intermediate | Normal to slightly decreased |
IV | Inhomogeneous, gray to black | Lost | Intermediate to hypointense | Normal to moderately decreased |
V | Inhomogeneous, black | Lost | Hypointense | Collapsed disc space |
An MRI of the right knee was taken using a Siemens 3T Trio MRI (Erlangen, Germany). The results were read by a single musculoskeletal radiologist blinded to the identity of the subjects. Each study was scored for degenerate changes according to the criteria of WORMS [
Statistical analysis was made using the Statistical Analysis System version 9.1 (SAS Institute Inc., Cary, N. C., USA). Nominal data were assessed with Chi-square. Interval variables were assessed visually for normal distribution and using the Kolmogorov-Smirnov test with a cutoff of 0.15. Normally distributed interval data were compared across the groups, using Student’s
Of the 295 recruits from the 1983 study, three received profiles because of knee problems and thirteen because of low back problems (
Twenty-six soldiers from the 1983 induction group were contacted by phone by the study’s senior author who was one of their army physicians in 1983. Twenty-five subjects agreed to participate. All of the 20 subjects contacted by the rabbi to participate in the study agreed to do so. Twenty soldiers and 17 Torah scholars had both maternal and paternal Ashkenazi origins. Table
Background characteristics of study populations (mean
Variable | Torah Scholars |
Soldiers |
|
---|---|---|---|
Age (years) | 43.7, 43.0, |
43.2, 43.0, |
0.9 |
Weight (kg in 1983) |
|
||
Recalled weight (kg in 1983) | 73.0, 73.5, |
73.7, 74.0, |
0.9 |
Years of education | 15.7, 14.0, |
15.9, 16.0, |
0.9 |
Packs years smoking | 4.3, 0.2, |
3.0, 0.0, |
0.26 |
Alcohol consumption (units/wk) | 0.3, 0.0, |
2.1, 1.0, |
0.01 |
The current anthropometric and physiological measurements (Table
Current anthropometric measurements and physiological measurements (mean
Variable | Torah Scholars |
Soldiers |
|
---|---|---|---|
Height (cm) | 176, 1.76 |
179.2, 179.0 |
0.02 |
Weight (kg) | 85.9, 85.3 |
84.5, 85.0 |
0.7 |
BMI | 27.8, 27.2 |
26.3, 26.6 |
0.3 |
There was a statistically significant difference between the current mean daily energy expenditure of Torah scholars and soldiers (
Current 24-hour energy expenditure in metabolic equivalents (METS) of Torah scholars versus soldiers (mean, median, and IQR).
Variable | Torah Scholars |
Soldiers |
|
---|---|---|---|
Mean daily total energy expenditure (METS) | 33.6, 33.4 |
44.1, 41.8 |
|
Mean daily energy expenditure in sports (METS) | 1.9, 1.2 |
8.1, 7.9 |
|
Generally, the Torah scholars avoided participation in sport as can be seen from a compendium of their continuous sport activity for the previous five years (Table
Compendium of continuous sports participation for the previous five years of Torah scholars versus soldiers.
Sport Activity | Torah Scholars | Soldiers | ||
---|---|---|---|---|
|
|
|||
No. of Participants | Hours/Week | No. of Participants | Hours/Week | |
Running ( |
0 | 0 | 13 | 4.6 |
Running (≤5 Km runs) | 0 | 0 | 2 | 1.5 |
Road or mountain biking | 0 | 0 | 12 | 2.6 |
Swimming | 1 | 4 | 8 | 1.9 |
Basketball | 0 | 0 | 6 | 2.8 |
Calisthenics/weight lifting | 2 | 3.3 | 4 | 1.7 |
Tennis/sQUASH | 0 | 0 | 2 | 0.8 |
Wind surfing | 0 | 0 | 1 | 4 |
There was no difference between the level and frequency of back or knee pain between the cohorts. Sixty-eight percent of soldiers and 70% of Torah scholars reported that they never suffered from back pain. Seventy-six percent of soldiers and 75% of the Torah scholars reported that they never suffered from knee pain. No difference in the degree of degenerative knee changes was found between the cohorts according to the WORMS score (Table
Knee and Back complaints and knee and back MRI findings (mean
Variable | Torah scholars |
Soldiers |
|
---|---|---|---|
Knee pain score (1–4) | 0.5, 0, 0.0–0.5 | 0.6, 0, 0.0–0.0 | 1.0 |
Back pain score (1–4) | 0.8, 0, 0.0–2.0 | 0.7, 0, 0.0–1.0 | 1.0 |
Worms score | 2.0, 1.5, 0.0–3.5 | 1.8, 1.0, 0.5–2.7 | 0.7 |
Pfirrmann score | 6.7, 7.0, 5.0–7.0 | 8.6, 9.0, 7.0–10.0 | 0.003 |
By univariate analysis, no statistically significant correlations were found between any of the anthropometic, physiological measurements or MET scores made in this study and the WORMS or Pfirrmann scores.
In this longitudinal study, the musculoskeletal health of knees and the lower back at middle age of two groups who were at the extremes of physical lifestyles since age 18 was compared. The study shows that very high skeletal loading did result in an increase in lumbar disk degeneration as assessed by the Pfirrmann score [
The extremely physically active group in this study was composed of former elite infantry soldiers who were subjects in a 1983 prospective study of stress fractures [
During the three years of compulsory military service, the soldiers marched long distances over difficult terrain carrying heavy loads. These loads were not supposed to exceed 40% of their body weight but often exceeded 50% of their body weights. During this same period, the Torah scholars sat long hours studying. After completing three or more years of regular army service, the soldiers continued to serve a month each year in reserve infantry units until the age of forty. During this time, they trained in the field wearing ceramic vests, while carrying their packs and weapons.
The great difference in the physical activity levels between the groups continued until the time of the 25-year review done in this study. The mean daily energy expenditure of the soldiers was a third higher than that of the Torah scholars. Most of this difference was because few Torah scholars participated in any sport or exercise activities other than walking to their place of study. The former elite infantry soldiers continued to do endurance sports such a running, mountain and road biking, and basketball.
In the current study, subjects were from a very narrow and well-defined genetic pool. Most were Ashkenazi Jews, with only a small portion being Sephardic Jews. Recent genetic studies have shown that these two populations are closely genetically related [
In vivo intradiscal pressure measurements allow us to understand how disc stress varies with different activities. During relaxed standing, the pressure has been measured to be 0.5 megapascals. In laboratory conditions, the intra disk pressure while lifting a 20 kg weight with the back flexed has been measured to be 2.3 megapascals [
Dimitriadis et al. [
In a longer term study, the effect of extremely high musculoskeletal loading on lumbar discs was evaluated before and after 14 weeks of Navy SEAL training [
Pye et al. [
Disc degeneration appears to be a complex process, combining mechanical, biochemical, histological, and genetic factors [
In the present study, the two groups were at the extremes of musculoskeletal loading. The soldiers at 25-year followup appear to have paid a price in their lumbar spines for this extreme loading. The amount of degenerative changes in the lumbar spine as evaluated by the Pfirrmann score was 27% higher in the soldiers than that of the Torah scholars.
The effect of short term high loading on knees has been studied by Hohmann et al. [
In a longer term study, the knees of ten Navy SEAL recruits were evaluated by MRI before and after a demanding 14-week training course [
Englund et al. [
There are several possible explanations for the greater long term resilience of the meniscus compared to that of the lumbar disks found in this study among the high loading group. One is that the heavy back packs carried by the soldiers in many of their activities repetitively placed higher stresses on the lumbar intervertebral disks than on the meniscus and thereby led to increased fatigue failure. Another explanation is that the meniscus may have better fatigue failure characteristics at repetitive high loading than the lumbar intervertebral disk.
This study compares the effect of extreme physical activities with an inactive life style on knees and the lower back at middle age using elite infantry soldier and Torah scholar cohorts. From an engineering stand point, this represents a test of very high versus very low sustained loading on these structures. The strength of the study is the uniform genetic backgrounds of the subjects. The main study limitation is the relatively small number of subjects in each of the two study cohorts. Even with this limitation, statistically significant higher lumbar disk degeneration was found in the elite infantry cohort. In spite of the extreme differences in the musculoskeletal loading between the cohorts, there was surprisingly little difference found by MRI criteria, in the amount of degenerative changes in both their knees and lumbar spines at middle age. The study indicates that the knee may possibly be more resilient to sustained heavy loading than are lumbar disks.
None of the authors have either an indirect or direct conflict of interests, including financial interests, that could in anyway affect their professional conduct and the validity of this research.